Indoor air pollutants, ventilation rate determinants and

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Indoor air pollutants, ventilation rate determinants and potential control strategies in Chinese dwellings: A literature review Article in Science of The Total Environment · May 2017 DOI: 10.1016/j.scitotenv.2017.02.047

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Science of the Total Environment 586 (2017) 696–729

Contents lists available at ScienceDirect

Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv

Indoor air pollutants, ventilation rate determinants and potential control strategies in Chinese dwellings: A literature review Wei Ye a,b, Xu Zhang b,⁎, Jun Gao b, Guangyu Cao c, Xiang Zhou b, Xing Su b a b c

State Key Laboratory of Pollution Control and Resource Reuse, Tongji University, Shanghai, PR China School of Mechanical Engineering, Tongji University, Shanghai, PR China Department of Energy and Process Engineering, Norwegian University of Science and Technology, Trondheim, Norway

H I G H L I G H T S

G R A P H I C A L

A B S T R A C T

• Indoor air pollution data measured in N 7000 residences in China were summarized. • Particulate matters, VOCs, SVOCs, moisture/mold, inorganic gases and radon were ubiquitous. • Ventilation prerequisites, determinants and requirements were discussed. • Natural (window) ventilation + air cleaner and mechanical ventilation + air filtration was compared.

a r t i c l e

i n f o

Article history: Received 30 June 2016 Received in revised form 27 January 2017 Accepted 6 February 2017 Available online 20 February 2017 Editor: J. Gan Keywords: Bioeffluent Particular matter VOC SVOC Mold Radon

⁎ Corresponding author. E-mail address: [email protected] (X. Zhang).

http://dx.doi.org/10.1016/j.scitotenv.2017.02.047 0048-9697/© 2017 Elsevier B.V. All rights reserved.

a b s t r a c t After nearly twenty years of rapid modernization and urbanization in China, huge achievements have transformed the daily lives of the Chinese people. However, unprecedented environmental consequences in both indoor and outdoor environments have accompanied this progress and have triggered public awareness and demands for improved living standards, especially in residential environments. Indoor pollution data measured for N7000 dwellings (approximately 1/3 were newly decorated and were tested for volatile organic compound (VOC) measurements, while the rest were tested for particles, phthalates and other semi-volatile organic compounds (SVOCs), moisture/mold, inorganic gases and radon) in China within the last ten years were reviewed, summarized and compared with indoor concentration recommendations based on sensory or health end-points. Ubiquitous pollutants that exceed the concentration recommendations, including particulate matter, formaldehyde, benzene and other VOCs, moisture/mold, inorganic gases and radon, were found, indicating a common indoor air quality (IAQ) issue in Chinese dwellings. With very little prevention, oral, inhalation and dermal exposure to those pollutants at unhealthy concentration levels is almost inevitable. CO2, VOCs, humidity and radon can serve as ventilation determinants, each with different ventilation demands and strategies, at typical occupant densities in China; and particle reduction should be a prerequisite for determining ventilation requirements. Two directional ventilation modes would have profound impacts on improving IAQ for Chinese residences are: 1) natural (or window) ventilation with an air cleaner and 2) mechanical ventilation with an air filtration unit, these two modes were reviewed and compared for their applicability and advantages and disadvantages for reducing human exposure to indoor air pollutants. In general, mode 2 can more reliably ensure good IAQ for occupants; while mode 1 is more applicable due to its low cost and low energy consumption. However,

W. Ye et al. / Science of the Total Environment 586 (2017) 696–729

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besides a roadmap, substantial efforts are still needed to develop affordable, applicable and general ventilation solutions to improve the IAQ of residential buildings in China. © 2017 Elsevier B.V. All rights reserved.

1. Introduction Building envelopes intentionally separate occupants from the outside, making indoor pollutants, such as particulate matter, inorganic gases, volatile organic compounds (VOCs), semi-volatile organic compounds (SVOCs), mold, and radioactive compounds (as summarized in Table 1), more easily to accumulate indoors. Some of the pollutants found indoors can produce odor or cause irritation, while many can pose chronic and/or acute health effects on occupants (Logue et al., 2011; Wouter Borsboom et al., 2016) via inhalation, dermal or other pathways (Gong et al., 2016; Ostro et al., 2015; Tischer and Heinrich, 2013; Tse et al., 2011; Tsushima et al., 2016; Weschler, 2009). Other than the available technologies for source control and air cleaning, ventilation serves as the basic means to partially dilute indoor pollutants, mostly in the gas phase, and to maintain a habitable space for human beings. Ventilation can be inefficient for reducing human exposure to radon (as the radon entry rates can be the leading factor sometimes) (Andersen et al., 1997), or significantly decrease SVOC concentrations both in the gas phase and on indoor surfaces including human skin (Liu et al., 2015). However, ventilation is still a common method with usually manageable costs. Furthermore, one of the key elements of using ventilation to improve indoor air quality (IAQ) is to determine an adequate ventilation rate in a standardized manner at a broader scale. In a sense, the required adequate ventilation can be interpreted as the recommended (minimum) ventilation rate for various buildings as specified in guidelines, standards, building codes or even legislation, and this ventilation rate is usually provided by mechanical ventilation systems (ASHRAE, 2016a; ASHRAE, 2016b; Brelih and Seppänen, 2011; BSI, 2008). However, it should be clarified that the recommended ventilation rate is an engineering approach based on available knowledges and technologies, and can be considered as prescriptions. Sometimes, people use the term of minimum ventilation rate when refereeing to the mandatory ventilation rates in building design codes, such as GB 50736-2012 in China (MOHURD, 2012). And to determine the recommended (or minimum) ventilation rate in practice is a comprehensive task for the following reasons at least: First, it is easy for engineers and building owners to follow this rate during the design phase to reach a target acceptable IAQ. On the other hand, it is also easy to be overlooked and poorly accomplished during both the design and service phases,

Table 1 Typical indoor air pollutants and their corresponding sources and causes. Pollutant category

Examples of substance SO2, NOx, CO, CO2, NH3, O3

Typical sources/causes

Metabolism, combustion processes; traffic emissions; reaction with organic compounds, etc. Building materials and Organic Volatile organic compounds; consumer products; gases/compounds semi-volatile organic compounds; (formaldehyde is solvents; cosmetics, etc. considered as a VOC in this review) Non-biological Smoke and dust; PM2.5; PM10 Combustion; road particles pollution; industrial sources; air-borne soil and sand, etc. Biological particles Dust mites; mold; pollen; Usually naturally occurring bacteria and organisms Inorganic gases

compromising occupants' living and working environments. Second, the recommended (or minimum) ventilation rate must balance improving IAQ, which usually requires more ventilation, with the energy consumption, which needs less ventilation (Sundell, 2004). Third, more diversified indoor air pollutant sources require flexible methods for determining the ventilation rate, while the regulations of the minimum ventilation rate in a standardized manner need to avoid complexity. The scientific minimum ventilation rate, on the other hand, is another topic of debates. In modern society, exposure to indoor compounds is almost inevitable regardless of where people live (Weschler, 2009). The ultimate question on indoor pollutants should be whether people are exposed to pollutant levels that are above health-based criteria. And the corresponding minimum ventilation rate should be adequate enough to minimize the health effects that indoor air pollutants can pose on occupants. In general, as summarized by (Carrer et al., 2015), available epidemiological data show that higher ventilation rates will reduce health outcomes and that there are minimum rates of ventilation above which some acute health outcomes can be avoided (the data on chronic health effects are still rare). But, no clear causality has been established and no universally applicable ventilation-health relationship can be established. The primary reason is that ventilation is indirectly related to health because it only modifies exposures to indoor and outdoor sources that affect health (Carrer et al., 2015). Therefore, ventilation rate should be strongly based on the strength of the pollutant sources that are present indoors. And therefore, indoor air pollutants that have unhealthy concentrations can be considered as ventilation determinants. In a broader sense, ventilation determinants include temperature, humidity, emissions from occupants (bioeffluents), and emissions from indoor materials, furniture and work processes (Persily et al., 2005; Zuraimi and Tham, 2008). This paper only considers the indoor pollutants that can be used to determine the ventilation rates to be ventilation determinants. Throughout the approximately 200-year history of the minimum ventilation rate, many indoor air pollutants, e.g., formaldehyde, VOCs, total volatile organic compounds (TVOC), SVOCs, and particles, have been discussed and proposed as potential determinants for the ventilation rate (Jokl, 2000; Liu et al., 2015; Noh and Hwang, 2010; Sherman and Hodgson, 2004; Ye et al., 2014c). At present, the regulated ventilation rate is primarily based on IAQ surrogates that represent the bioeffluent mostly emitted from humans, such as CO2 and odor. Due to the groundwork laid by Pettenkofer (1858) and Yaglou et al. (1936), the link between the minimum ventilation rate and CO2 (or odor) has been extensively studied. The idea of determining the minimum ventilation rate based on sensory end-point (odor and irritation) has been further developed in the concept of perceived IAQ (Fanger, 1988). Ultimately, the ventilation rate should be more dependent on the health end-point of indoor pollutant exposure, such as short- and long-term health consequences, instead of on occupants' perception of IAQ alone (Sundell et al., 2011). It was not until recently that moderate concentrations of bioeffluents with CO2, not pure CO2, were proven to be a causative agent and to have deleterious effects on acute health symptoms and cognitive performance of occupants during typical indoor exposures (Zhang et al., 2016a). This result suggests that to dilute the concentrations of indoor bioeffluents is not only an effort for sensory-related purposes, but also a measure to avoid potential health effects. This is an epitome to the limited but growing scientific bases to determine ventilation rate. As (Persily, 2015) summarized, there are many challenges and efforts in developing ventilation rate standards, and to date, the purpose of recommending adequate ventilation rate shifts

698


from covering sensory issues alone to providing a more health-oriented approach for indoor environment in buildings. After many years of studying and debating, in 2012, China launched its revised national design standard for heating, ventilation and air conditioning (HVAC) for civil buildings that is still in effect (MOHURD, 2012). Although during the revising process, it still took sensory-based ventilation rates as references to a great extent, this standard has been playing an important role in standardizing the ventilation design for buildings in China. In this standard, the minimum ventilation rates (as in an engineering aspect) that cover N30 types of spaces with various functions fall into four categories: public buildings (not high occupant density buildings), residential buildings, hospitals and high occupant density buildings. Compared to the previous standard published in 2003 (MOHURD and AQSIQ, 2003), almost all of the defined spaces were brought together for the first time. Another landmark change involved categorizing buildings using occupant density based on the assumption that human bioeffluents can be the dominant pollutants in high occupant density buildings. The minimum ventilation rate per person (m3 h−1 ∙ person−1) was simplified and given based on the occupant density (person m−1) for high occupant density buildings, e.g., classrooms, supermarkets, cinemas, libraries and stadiums. On the other hand, the minimum ventilation rate was given as the minimum air change rate (ACH, h−1) based on the average area per person (m2 ∙person−1) value for dwellings that have a mechanical ventilation system to supply outdoor air to the indoors, as shown in Table 2. (Dwellings that do not have a mechanical ventilation system to supply outdoor air do not have a regulation for the minimum ventilation rate.) For many years, residences were considered to be low occupant density spaces; building pollutants, e.g., VOC emissions from building materials and consumer products, are sometimes the majority of the indoor pollutants in low occupant density spaces (Ye et al., 2014b). However, current ventilation rates for residences are still mainly based on human bioeffluents and may not suitably account for potential pollutants other than bioeffluents, e.g., particles, VOCs and SVOCs, in the residential environment.

For comparison, the typical methods used to determine the ventilation rate in the EU and USA are included in Table 2 (ASHRAE, 2016a; ASHRAE, 2016b; BSI, 2007; Cao et al., 2012). Although many European countries also have various regulations or guidelines on ventilation rate (Brelih and Seppänen, 2011), only EN 15251 is shown as an example to represent the European efforts and typical methods. As opposed to using the air change rate for the whole room to regulate the residential ventilation rate in China, the ventilation rate per person is more frequently used in both the EU and USA. However, using default values of n, A or Nbr, the typical air change rate (~0.5 h−1 to ~0.7 h−1) would be similar to the values in China. Although it is difficult to tell which method is more advanced in general, it can be noted intuitively that both the EU and USA methods are more occupant-oriented (e.g., determining the ventilation rate based on expectations or partly on occupant number), while the Chinese method is less complicated (in terms of calculation), but is more building-oriented (based on the area per person). Furthermore, both EN 15251 and ASHRAE 62.2 have emphasized not only the need to apply mechanical ventilation in residences but also the need to adjust the exhaust air from the kitchen, bathrooms and toilets; outdoor air should primarily be supplied to living rooms and bedrooms. The current Chinese ventilation rate standard is still general and has little impact on dwellings that do not install a mechanical ventilation system to supply outdoor air. This discussion on ventilation rate standard leads to two more topics. First, ventilation can be poor in reality, no matter how much the ventilation rate is recommended or even regulated. Home ventilation is mainly occupant controlled. Even with proper design, it is very difficult to make it mandatory for everybody to use home ventilation when necessary. (Dimitroulopoulou, 2012) reviewed ventilation data in European dwellings, and the results show that although occupants generally think that ventilation is important, their understanding of the ventilation systems is low, often resulting to under-ventilated homes (lower than 0.5 h−1, which is currently a standard in many European countries).

Table 2 Determining the minimum ventilation rates for residential buildings in China, Europe and the USA. Country/region

Standard

Criteria

China

GB 50736-2012

Area occupant density (m2 ∙person−1)

Europe

EN 15251: 2007

Expectationa

USA

ASHRAE 62.2-2016

For dwelling unit ventilation

Conditions

Minimum ventilation rate Living room/bedroom

Kitchen/bathroom/toilet

≤10 (10, 20) (20, 50) N50 I (high expectation)

For mechanical ventilation: 0.70, h−1 For mechanical ventilation: 0.60, h−1 For mechanical ventilation: 0.50, h−1 For mechanical ventilation: 0.45, h−1 max(0.49A, 10n + 1.4A), L·s−1b

Kitchen, bathroom

3.0 h−1

II (normal expectation)

max(0.42A, 7n + 1.0A), L∙s−1b

III (moderate expectation)

max(0.35A, 4n + 0.6A), L s−1b

Bedroom number based

0.15A+ 3.5(Nbr + 1), L s−1c

Kitchen Bathroom Toilet Kitchen Bathroom Toilet Kitchen Bathroom Toilet Enclosed kitchen

28 L s−1 20 L s−1 14 L s−1 20 L s−1 15 L s−1 10 L s−1 14 L s−1 10 L s−1 7 L s−1 50 L s−1d 150 L s−1 or 5 h−1e 5 h−1f 50 L s−1d 150 L s−1d 25 L s−1d 10 L s−1f

Non-enclosed kitchen Bathroom a

The detailed definitions of the criteria can be found in (BSI, 2007). The logical equation is for determining the total ventilation rate for the residence, where n and A are the number of occupants and the room floor area, m, respectively. The exhaust airflows from the kitchen, bathroom and toilets should be adjusted accordingly. c The equation is for determining the total ventilation rate, where Nbr is the number of bedrooms. d Demand-control local exhaust using a vented range hood (including appliance-range hood combinations). e Demand-control local exhaust using other kitchen exhaust fans, including downdraft. f Continuous local exhaust. b


Second, the applied ventilation method should be able to efficiently remove or dilute the concentrations of indoor pollutants. However, most of the residential buildings in China still depend on “window ventilation” or infiltration to passively introduce outdoor air to indoors. Although mechanical ventilation often comes with an air filtration unit that provides a reliable way to supply the minimum required airflow with good air quality to indoor spaces, this ventilation method has not been popularized among Chinese dwellings due to economic and many other factors. In reality, instead of depending on the mechanical ventilation, opening windows often becomes a life-long habit among Chinese people (Peng et al., 2012). This occupant-controlled window ventilation is often mistaken as natural ventilation, while natural ventilation should be designed specially to use natural forces for building ventilation. With suitable climate and proper design, natural ventilation can be an energy-efficient way to improve IAQ. However, at least three downsides can still be expected. 1) Natural ventilation is not always predictable or sufficient. Building location, group layout, orientation, internal space arrangement and openings need to be carefully designed to maximize natural ventilation. For example, in the past, natural ventilation was used along with sun shading and thermal insulation to make traditional Chinese dwellings passively climate responsive in the rural areas with hot summers and cold winters (Gou et al., 2015); however, thermal sensation during winter was not satisfactory. Currently, approximately 250 million households (accounting for 55% of the population) live in cities. Compared to 2001, the total number of residents living in rural areas in 2014 dropped from 796 million to 619 million, while residents living in urban areas increased from 481 million to 749 million (NSB, 2015). Consequently, natural ventilation potential in multi-story or high-rise apartment buildings has become an emerging topic in China (Zhou et al., 2014). In terms of sufficient quantity, China is currently the largest producer of wood-based panels, coatings and furniture in the world (Liu et al., 2012); therefore, massive new building furnishing materials and consumer products have emerged in people's daily life. Exposure to ubiquitous VOCs and SVOCs is already causing public concerns; asthma, rhinitis and eczema (allergic or non-allergic) have been increasing among children during the last several decades, indicating that insufficient ventilation rates in homes and schools can be a problem (Zhang et al., 2013b). 2) Outdoor air quality is of wide concerns for many parts of the country (Hua et al., 2015; Li and Zhang, 2014; Wang et al., 2014a). The haze event on January 30, 2013, affected 1.43 million square kilometers, covering approximately 15% of China's land territory (MEP, 2013). Natural ventilation is theoretically unhealthy to use in areas with severe outdoor pollution unless the air has been properly treated. Currently, air cleaners are an affordable household solution that are usually used for only some spaces and some of the time. Although air cleaners can be reasonably effective even under haze conditions with window ventilation (Ma et al., 2016), none of the current technologies for air cleaners are able to effectively remove all indoor pollutants, including particles and VOCs, and many could generate undesirable by-products during operation (Zhang et al., 2011a). Therefore, whether air cleaners can be useful in dwellings may not have a straight answer. 3) The natural ventilation approach for home ventilation makes the minimum ventilation rate regulated by national standard (MOHURD, 2012) less effective and guaranteed. In a way, the minimum ventilation rate should mainly be achieved by mechanical ventilation. Some of the newly built residential buildings are equipped with mechanical ventilation to supply filtered outdoor air into the indoor environment. However, the majority of residences are existing dwellings that mostly depend on window or natural ventilation, making effective and affordable indoor air cleaning devices a necessity.

699

Rapid modernization and urbanization has led China to experience a dramatic change in both indoor and outdoor environments during the past two decades. The challenges that urge us to improve IAQ for 1.4 billion residents have never been more urgent and complicated. Although the current ventilation standard in China (MOHURD, 2012) has refined the ventilation requirements for various buildings and has already led to industrial development of related technologies and products, the contents are still partially derived from international experience. Because the adequate ventilation rate is closely related to strength of the pollutant sources and efficacy of the ventilation design and system, both aspects need to be thoroughly investigated in the context of Chinese dwellings. This review first focuses on current major indoor pollutants, i.e., bioeffluents, particles, VOCs, SVOCs, mold/moisture and radon, based on both sensory (mainly for bioeffluents) and health end-points, in residential buildings in China, by reviewing the available scientific literature and summarizing the indoor concentration data. Applicable ventilation determinants that have adverse acute and chronic effects on health are discussed, followed by a discussion and comparison of the methods used to determine ventilation requirements. In addition, two ventilation modes raised in recent years that specifically intended for ventilation in Chinese residential buildings, i.e., natural ventilation (mainly window ventilation) with an air cleaner (mode 1) and mechanical ventilation with an air filtration unit (mode 2), are compared in terms of their applicability and adaptability in China. Mode 1 is assumed to be able to meet the ventilation rate requirements, although the current GB 50736-2012 standard only applies to dwellings that have installed mechanical ventilation systems. Both modes have the potential to achieve good IAQ. However, the difference is that mode 1 does not actively target the minimum ventilation rate, while mode 2 intentionally meets this requirement. The competition and comparison of the two modes are currently popular topics for national discussions and debates as part of the 13th Five-Year Plan cycle (2016 to 2020) as they are possible solutions for improving IAQ in the dwellings. It needs to be pointed out that there are many ways that can be used to achieve good IAQ in dwellings. In addition, many modifications can be done based on each one of the modes. However, these two modes represent two directions for home ventilation development and open a dialog for more discussions and debates on whether we should popularize mechanical ventilation or promote air cleaners to improve residential IAQ, while overcoming outdoor air pollution on a large scale with limited room for increasing total energy usage in the residential sector. Since no conclusive studies have been proposed to prioritize these two technological pathways, and no final results may end this debate at least for the next few years, a comprehensive review is needed to analyze the potentials of the two primary options. 2. Method 2.1. Overall approach The overall approach of this work is to focus on specific issues in China by taking the following steps. First, the concentrations of typical indoor pollutants that have been measured in Chinese residential buildings from both English and Chinese literature are reviewed and summarized (in Section 3). Although specific ventilation rate data are limited and therefore excluded, the potential exposure pathways to the target indoor pollutants and the key influencing factors (e.g., human behavior) involved in the ventilation process are included. Second, ventilation prerequisites and determinants are discussed (in Section 4), based on the typical indoor and outdoor source strength. The concentration recommendations for typical indoor air pollutants are summarized as well as both acute and chronic health effects. The measurement data obtained in Section 3 were used to compare with the concentration limits for the role of being ventilation determinants.

700


Third, possible control strategies to determine ventilation requirements are discussed (in Section 5). Because a universally applicable method for determining the ventilation rate for residential buildings in China may be difficult to establish, methods to meet the ventilation requirements for key determinants are discussed separately. The discussion on the ventilation requirements is not extensive, mainly because the ventilation requirement is strongly related to the indoor concentration threshold and health effects. Moreover, the discussion on ventilation determinants and requirements is mostly provided to discuss the two highlighted ventilation modes. Finally, the advantages and disadvantages of the two highlighted modes are analyzed and compared (in Section 6). Future directions for improving the residential IAQ in China are recommended (in Section 7). More discussion is encouraged to better utilize the technologies and to balance cost and living standards. The ventilation effectiveness of the two ventilation modes is not included in the review as this issue has been substantially reviewed by (Cao et al., 2014). 2.2. Literature search method The scientific literature was collected by searching through several major databases for literature in English, i.e., ISI Web of Science (SCI-Expanded, 1994 to present), ScienceDirect (1823 to present), EI Compendex (1969 to present), PubMed (1946 to present), Wiley (1997 to present), and two major databases for Chinese literature, i.e., CNKI (1979 to present) and Wanfang Data (1990 to present). Google Scholar was also used as a supplementary search method. The searches included the following keywords (the keywords were translated into Chinese when searching for literature in the Chinese databases): ● Keywords related to indoor environments in residential buildings: urban, rural, indoor, resident, residential, residence, dwelling, home, house, household, dwelling, apartment, indoor, indoor environment, ventilation, natural ventilation, mechanical ventilation, ventilation rate, ventilation requirement, air filtration, air cleaner, occupant behavior, occupant behavior, exposure ● Keywords related to air pollutants: particulate matter, particles, particulates, gas-phase, pollutant, air pollutant, air contaminant, airborne pollutant, airborne, concentration, contaminant dust, PM1.0, PM2.5, PM10, odor, odour, bioeffluent, breath, CO, carbon monoxide, carbon dioxide, CO2, ozone, O3, nitrogen dioxide, NO2, sulfur dioxide, SO2, ammonia, NH3, volatile organic compound, VOC, total volatile organic compound, TVOC, formaldehyde, benzene, toluene, ethylbenzene, xylene, styrene, BTEX, semi-volatile organic compound, SVOC, phthalate, PAH, DEHP, DBP, mold, mould, moisture, fungi, dampness, radon ● The keyword “China” was included in most of the English language searches. ● Additional papers were added after the preliminary searches based on specific topics. Original research journal and review articles published up to June 2016 were included in the searches (while textbooks, guidelines, standards, patents, and newspapers were excluded), over 100,000 articles in the two languages were identified. Because numerous publications that have extensively reviewed concentrations of indoor pollutants in China during the past are available, this paper specifically focuses on the indoor concentration data in the scientific literature within the past ten years (from 2006 to 2016) to reflect the recent status and changes due to rapid modernization and urbanization for residential buildings in China. In addition, because indoor pollutant concentrations and ventilation requirements were the focus of this paper, indoor sources and exposure status are briefly discussed. Detailed outdoor sources and health effects of indoor pollutants were excluded from this review. However, because odor can typically be used as a direct determinant for ventilation, partially because Yaglou's method had a

profound impact on determining ventilation in China, the sensory comfort issue was included in this review. Thus, N600 articles were selected as relevant based on their publication dates, titles and abstracts. Because the majority of the references needed in this paper need to contain reliable measurement data of indoor pollutants, the description of the measurement had to be adequate, and the measurement method should follow standards such as GB/T 18883-2002 (AQSIQ et al., 2002) or other appropriate procedures. Moreover, the data should be presented based on appropriate statistical analysis. A mean value (with standard deviation) or a measurement range was considered as informative, while a percentage of the measurements that passed a certain threshold (e.g., a concentration limit provided by a standard) was not. Thus, the number was further reduced to ~240 articles based on the full content. Furthermore, even though a ventilation rate standard should apply to residential buildings in both urban and rural areas, currently, it is more practical to focus on residences in urban areas where the highlighted ventilation rate methods are less difficult to generalize. In addition, the quantity of data available on air pollution in urban residences was overwhelmingly larger than that in rural residences, except for particle and radon measurements. As a result, the particle and radon data summarized in this review covered both urban and rural residences, while the VOC, SVOC, moisture/mold and inorganic gas data were mainly for the urban residential environment. 3. Indoor/outdoor pollutant concentrations 3.1. Data on indoor bioeffluents Indoor bioeffluents are mainly generated indoors, and as discussed in the Introduction section, bioeffluents are worthy of discussing from both sensory (odor and irritation) and health endpoints. In general, bioeffluents can be mainly produced by exhaled breath, as well as dermal emissions. Certain VOCs that have sensory effects can be emitted or produced by both means. VOCs in human breath were identified as early as 1970; since then, they have been taken as noninvasive indicators of individual health in medical studies (Fenske and Paulson, 1999; Marco and Grimalt, 2015). Emissions from humans include hydrocarbons, alcohols, ketones, and aldehydes and normally occur at ppbv to ppmv levels (Fenske and Paulson, 1999), and the total number of VOCs that emanated from exhaled breath can be up to N800 (de Lacy et al., 2014). Variations in composition and concentration of the VOCs emitted by people are expected; health, occupational exposure and habits (such as smoking) can all be influencing factors (Fenske and Paulson, 1999). Recent evidence has also specifically shown that the human breath rate increases when exposed to air pollutions (Mu et al., 2014). Regarding odor and irritation, according to (Devos et al., 1990; Ruth, 1986), some VOCs can produce odor or cause irritation. However, prediction of odor or irritation could be hard. First of all, although the odor or irritation caused by single compound can be quantified, the combined sensory effects of multiple odors are complex. In addition, due to differences in experimental methodologies and human olfactory responses, odor threshold data usually vary considerably (e.g., up to four orders of magnitude for one chemical substance) (Cain and Schmidt, 2009). Despite this inconsistency, the estimated indoor concentrations are probably far less than the olfactory threshold or irritating concentration because of the low occupant density of these buildings. Table 3 summarizes the reported concentration, olfactory threshold and irritation concentration for five major VOCs from exhaled breath. The steady state concentrations of the exhaled VOCs are determined to be below 100 μg m− 3 at ACH = 0.5 h−1, which are all less than the olfactory thresholds or the irritating concentration for the corresponding VOCs. On the other hand, evidences also have shown that dermal emissions, or rather chemical reactions between ozone and skin lipids can create pollutants that may cause sensory nuisance (Tsushima et al.,


701

Table 3 Indoor steady state VOC concentrations at ACH = 0.5 h−1 for selected major VOCs that are exhaled by humans assuming the following: a) the concentration differences between the VOCs exhaled from Chinese people and the subjects tested in the reported study are neglected; b) the respiratory rate is 7.5 L·min−1; c) the average volume per person is 70 m3 ∙person−1; and d) the indoor air is well-mixed at steady state. Chemicals

Acetone Ethanol Methanol Ethylene Methyl ethyl ketone a

VOCs in exhaled air

Exhaled VOCs concentrations at steady state, μg·m−3

Concentration, μg·m−3

Reference

3–4875 26–2057 229–2860 NDa–291 ND ~ 146

(Fenske and Paulson, 1999)

Olfactory threshold and irritation concentration Low ~ high odor threshold, μg·m−3

0.04–62.7 0.34–26.4 2.9–36.8 0–3.8 0–1.9

4.7 3.4 1.3 3.0 7.4

× × × × ×

104–1.6 × 106 102–9.7 × 106 104–2.7 × 107 105–4.6 × 106 102–1.5 × 105

Irritating concentration, μg·m−3 4.7 9.5 2.3 – 5.9

× 105 × 106 × 107

Reference

(Ruth, 1986)

× 104

Not detected, similarly hereafter.

2016; Wisthaler and Weschler, 2010). Besides skin, odor can also come from indoor ozone-initiated reactions with clothes, hair, or other materials (Weschler, 2016; Weschler et al., 2007). Detailed chemical reactions in indoor environments are beyond the scope of this paper; references such as (Nazaroff and Goldstein, 2015; Weschler, 2011) may be helpful for further investigation. Overall, the total amount of VOCs emanated from human breaths and skins may be negligible compared to other sources, such as building materials (Ye et al., 2014a) (also see Section 3.3). Because dwellings in China are usually low occupant density spaces (~28 m2 ∙person−1 and 39 m2 ∙person−1 for residential buildings in urban and rural China, respectively) (NSB, 2015; THUBERC, 2016), the VOCs emitted from humans that contribute to indoor air can be estimated as less than ~ 101 μg∙m−3 in total at normal ventilation conditions. However, caution should be taken that certain VOCs may cause sensory effects at very low concentrations. For example, although the chemical concentrations stemmed from ozone-initiated reactions on skin can only be at pptv to ppbv levels, some of the volatile products, especially the dicarbonyls, may be respiratory irritants, and some of the less volatile products may be skin irritants (Wisthaler and Weschler, 2010). In terms of health effects, CO2 can be used as an indicator for bioeffluents in indoor environment, as reviewed in Introduction. In residential buildings, CO2 comes mainly from human metabolism (in addition to cooking processes in the kitchen). The concentration of CO2 in exhaled air is two orders of magnitude higher than in the ambient air and is usually between 40,000 and 55,000 ppmv (Zhang et al., 2016a), resulting in variations of CO2 concentrations in indoor air. Two recent studies have adapted the metabolism-based CO2 generation rate to Chinese people. First, a well-known empirical model that links the CO2 generation rate with metabolism was given by (Nishi, 1981); however, corrections with a factor of 0.75 for Chinese females and 0.85 for Chinese males were proposed by (Qi et al., 2014). Second, the methods presented by (Luo et al., 2016) suggested that the human metabolism rate vary at different activity levels or thermal sensations to further affect CO2 concentrations. Another issue associated with indoor CO2 exposure is that the background concentration has considerably increased due to climate change; the average atmospheric CO2 in 2008 reached a concentration of 385 ppmv, which is 38% higher than pre-industrial levels (Le Quere et al., 2009). The monthly CO2 concentration level recorded by Mauna Loa Observatory in Hawaii even surpassed 407 ppmv in May, 2016 (CO2.Earth, 2016). However, experiments show that no statistically significant effects on the perceived air quality, acute health symptoms, or cognitive performance were found when CO2 reached up to 3000 ppmv. Moderate concentrations of bioeffluents, but not pure CO2, result in deleterious effects on occupants during typical indoor exposure (Zhang et al., 2016a), making CO2 a potential representation of air pollution but not a causative agent in typical indoor environments.

3.2. Data on indoor/outdoor particulate matter As stated by WHO (2006), numerous sources of evidence show that inhaled particles have adverse health consequences for the lungs and other organs. (Lelieveld et al., 2015) estimated that outdoor air pollution, mostly by PM2.5, leads to 3.3 million premature deaths per year worldwide, predominantly in Asia. Among all the air pollutants, the most urgent health concern raised by the public in China today is probably particulate matter. In indoor environment, primary particle sources include both outdoor particles (via natural or mechanical ventilation and infiltration) and indoor combustion activities (e.g., cooking, environmental tobacco smoking, kerosene heating and wood burning) (Chen and Zhao, 2011; He et al., 2004). The vast majority of the particles generated by combustion fall in the domain of submicrometer particles (Morawska and Zhang, 2002). Indoor secondary organic aerosol (SOA) formation may also contribute to particle concentrations as secondary particles within residences (Waring, 2014); ozone acts as an important driver in the formation of SOAs (Iinuma et al., 2013; Waring and Siegel, 2013). To some extent, the building envelope can be considered as a particle sink; however, human movement may also cause resuspension of coarse particles (Tian et al., 2014). As reviewed by (Chen and Zhao, 2011), the relationship between indoor and outdoor particle concentrations can be described and assessed by the following indicators: indoor/outdoor (I/O) concentration ratio, infiltration factor and penetration factor. Although the I/O ratio may not be as useful as the other two indicators when accounting for indoor particles that originated outdoors, this relationship is particularly important because residential buildings in China are not usually equipped with mechanical ventilation systems. Therefore, there is almost no positive pressure in homes to prevent outdoor particles from moving inside. In addition, the airtightness of the walls and windows for residences in China is low (Wang et al., 2015a), suggesting that particle penetration would still be a problem even if mechanical ventilation was added to homes. Tables 4 and 5 summarize the published data on indoor and outdoor particle concentrations for urban and rural residential buildings, respectively, in 14 provinces and municipalities (Beijing and Tianjin) in China with normal ventilation conditions. The data for three typical particle sizes, i.e., PM1.0, PM2.5 and PM10, that were all measured within the past 10 years are included. In the urban residential context, in addition to the measurement periods, locations, and climate zones, whether the district heating is on and the room functions are also specified. The 11 studies included in Table 4 cover four climate zones: 1) severe cold; 2) cold; 3) hot summer and cold winter; and 4) hot summer and warm winter; most of the target pollutants are PM2.5. Although the climate condition plays an important role in using window or natural ventilation to dilute indoor pollution, none of eight cases show essential

702

Table 4 Summarized data measured over the last 10 years of indoor and outdoor particle concentrations for urban residential buildings in China with normal ventilation conditions. Location & climate zone

Measured period

District heating

Number of residences

Room function

(Wang et al., 2016a)

Nanjing: hot summer and cold winter Huzhou: hot summer and cold winter Lanzhou: severe cold

2014.12–2015.01

No

Living room

2013.02–2013.03

Yes

1 1 1 1 53

2013.09

No

54

PM1.0 concentrations mean (min, max), μg·m−3 Indoor

(Fan et al., 2014; Li et al., 2016)

(Dong et al., 2015) (Zhang et al., 2014c) (Cheng et al., 2009) (Liu et al., 2013a; Sun et al., 2014) (Wang et al., 2013)

Xi'an: cold Beijing: cold

(Xue, 2012)

Nanchang: hot summer and cold winter Shenzhen: hot summer and warm winter

(Zhang et al., 2011b)

a b c d e

Tianjin: cold Nanjing: hot summer and cold winter

2011.01 2013.05–2014.04 2008.10 2011.11–2011.12 2012.11

Yes Yes No Yes No

5 571 8 42c 85

2009.06 2010.01 2008.12

No

30

No

28

Bedroom Kitchen Bedroom Kitchen Dormitory Not specified Living room Living room Living room Bedroom Kitchen Dormitory

a

Outdoor

b

a

73 (37, 120)

109 (69, 180)

68 (22, 215) 67 (22, 212) 67 (5, 246)

72 (34, 132)

Living room Bedroom Kitchen

The mean value was calculated based on all of the mean concentrations for the datasets measured from five dormitories. Due to lack of original data, the minimum and maximum values were calculated based on the mean value and standard deviation for each dataset. Forty-two children were observed in their homes, and the number of residences were assumed to be equal to the number of children. The indoor and outdoor data came from two different sources that covered a similar period of time. The median was used instead.

b

PM2.5 concentrations mean (min, max), μg·m−3

PM10 concentrations mean (min, max), μg·m−3

Indoor

Outdoor

Indoor

Outdoor

65 (32, 165) 40 (22, 75) 26 (11, 63) 42 (24, 73) 125 (48–279) 119 (38, 368) 80 (9, 388) 80 (14, 212) 76a (38, 123)b 86 (4, 338) 59 (6, 667) 114 (47, 249) 81 (37, 296) 80 (36, 267) 79 (12, 312) 117 (87, 164) 119 (95, 161)

75 (36, 178) 90 (37, 169) 138 (64, 280)

103a (46, 197)b

177a (103, 281)b

328 (225, 530) 80 (40, 166) 112a (73, 184)b 124 (10, 710) 74 159 (30, 292)d 85 (42, 155)

90 (54, 120) 122 (83, 187)

123 (74, 163) 186 (110, 221) 241e (101, 1080) 239e (87, 892) 271e (97, 842)


Reference

Table 5 Summarized data measured over the last 10 years of indoor and outdoor particle concentrations for rural residential buildings in China with normal ventilation conditions. Location

Measured period


Fuels type

Room function

(Wu et al., 2015)

Baofeng County and Fangcheng County in Henan

2012.09–2012.10

12

Crop residues, coal, gas, electricity

2013.01

Guizhou

2011.11–2011.12

Living room Kitchen Living room Kitchen Bedroom Kitchen Bedroom Kitchen Kitchen

(Ma et al., 2015)

(Gong et al., 2014b)

(Shao et al., 2013)

(Wang et al., 2010c)

Coal

1

Firewood Biomass: firewood, corn or wheat stalk, etc. Coal Liquefied gas Biogas Coal

Hubei, Hebei, Liangning, Guizhou, Guangdong

2009.07–2011.05

24

Hutou Village in Yunnan Xize Village in Yunnan Guaiji Village in Guizhou

2007.02

18 14 2 2

2008.05

2 2–3

Dongtai County in Jiangsu

1

Wet-coal Coal Straw

Kitchen

Firewood (Gao et al., 2009b)

a b c d e f

Jiangzi County and Zhanang County in Tibet

2006.12–2007.03

Not specified, totally 118 valid samples

Indoor

Outdoor

108a (36, 177)

193a (73, 418) 290a (93, 764) 392a (108, 1024) 473a (66, 801)

189a (116, 386)

106

41

56 85c 305b 104b 112c 239b 240b,c

23 67

283a (52, 468)

Solid biomass fuel: Dung cake, wood, or methane

Living room Bedroom Kitchen

74c 296b 89b 83c 173b 198b,c 122 (87, 165) 88 (70, 108)d 104 (93, 134) 63 (50, 64)d 104 (86, 121)e 76 (57, 95)e 135 (84, 186)e

554a (240, 1250)

167 99 620c,f

680c,f 320c,f

Coal/wood

2–3

2008.04–2008.05

Outdoor

116a (32, 221) 156a (58, 333) 259a (94, 552) 300a (48, 584) 181 223 79 130 2610 (310, 13,320)b,f

Living room

Kitchen

PM10 concentrations mean (min, max), μg·m−3

Indoor

430 (134, 1220)b,f 360 (110, 1160)b,f 330 (50, 2290)b,f

Wood Biogas

Qianfeng village in Guizhou (Gu et al., 2009)

1

PM1.0/2.5 concentrations mean (min, max), μg·m−3

59

74

50 (40, 60)b 24 (11, 36)b,d

86


Reference

78 (60, 97)e

The data were calculated based on multiple datasets and may not be as rigorous as the actual mean value. The data were measured indoors while cooking activities occurred. The data were measured indoors without any cooking activities. The data were measured on rainy days. 95% confidence interval. The data were measured for PM1.0, while the rest were for PM2.5.

703

704


differences in terms of the particulate matter concentrations for all three sizes. All the outdoor mean PM2.5 concentrations are close to or N75 μg m−3, which is the 24-h average concentration limit (class II) regulated by GB 3095-2012 (MEP and AQSIQ, 2012). The effects of district heating on outdoor particle concentrations can be observed, the extremely high outdoor PM2.5 concentrations (530 μg m−3 in Lanzhou and 710 μg m−3 in Beijing) reported in Table 4 are measured during the heating season. The maximum outdoor PM2.5 concentrations among different cities in non-heating season are typically below 300 μg m−3. Most of the indoor PM2.5 concentrations are lower than the outdoor concentrations; however, the concentrations are significantly higher than the indoor PM2.5 concentrations recommended by WHO and American Society of Heating Refrigerating and Air-conditioning Engineers (ASHRAE) (15 μg m− 3 and 35 μg m−3, respectively) (ASHRAE, 2016a; WHO, 2006). Regarding the room space function, in general, the measured indoor PM2.5 concentration ranges for living room, bedroom and kitchen are 11 μg m−3–667 μg m−3, 9 μg m−3–388 μg m−3, 12 μg m−3–368 μg m−3, respectively. Theoretically, a kitchen should be the main indoor particle source that is most likely to result in high particle concentrations (Gao et al., 2015); however, neither the mean concentration nor maximum concentration differences among the living room, bedroom and kitchen are not significant based on the limited data listed in Table 4. One of the reasons could be due to low time resolution for the measurements. In terms of PM1.0 and PM10, most of the reported data were not significant, except for PM10 data in Shenzhen (a southern city in China) in winter, surprisingly high maximum indoor PM10 concentrations are measured. Table 5 provides a recent picture of the indoor/outdoor particle issue for Chinese people who live in rural areas. Except for one case, i.e., the data measured in Henan in January, 2013 by (Wu et al., 2015), all the mean and maximum outdoor PM2.5 concentrations are below (or around) 100 μg m−3 and 200 μg m−3, respectively. Although the outdoor particle concentrations originated from traffic or district heating is usually much less in rural areas compared to that of in urban cities, the outdoor particle concentrations in rural areas can also come from agriculture actives, e.g., straw burning, and decentralized heating, however, probably in a smaller amount in general. Despite the outdoor particle concentrations being better in some of the rural areas than in the urban areas, the indoor particle issue is also serious, especially when burning biomass or other fuels in the kitchen without proper ventilation (e.g., using a chimney). The maximum mean indoor concentrations of PM1.0, PM2.5 and PM10 are reached 2610 μg m− 3 (in kitchen), 300 μg m− 3 (in kitchen) and 473 μg m− 3 (in living room), respectively. The particle concentration differences among the kitchen, bedroom and living room are not significant because sometimes the kitchen is not properly isolated from the rest of the residence. Take PM2.5 for example, the measured ranges in kitchen and living room are 50 μg m− 3–584 μg m−3 and 32 μg m−3– 552 μg m−3, respectively. Furthermore, the fuel types have significant effects on the indoor particle emissions, concentrations and human exposure, using gas or electricity can significantly reduce indoor cookinggenerated particles; another issue that has not been fully addressed in the research is small diameter particles (smaller than PM1.0) in rural residences in China. Among the seven studies listed in Table 5, only one study measured PM1.0 when burning biomass, coal, liquefied gas or biogas, and the reported mean and maximum concentrations were extremely high (Gong et al., 2014b). Due to the limited indoor particle concentration data (and perhaps also limited studies) for urban and rural residences in China, it is not rigorous to draw any solid conclusions for indoor PM2.5 concentrations from Tables 4 and 5. However, the following aspects should be mentioned. First, indoor particle exposure in residential buildings is probably on a national scale that can be identified from south to north and from west to east. Because mechanical ventilation is not widely used,

building design should be further oriented toward the different climate zones to maximize the natural ventilation potential. Second, given that most of the reported data are daily-averaged, the mean particle concentration differences between the kitchen and other rooms are not significant. However, unhealthily high concentrations of particles can be still identified in the kitchen (Gao et al., 2015; Lai and Ho, 2008). More in situ studies with better time resolution are recommended for Chinese residential kitchens to capture and record the high instantaneous particle concentrations during cooking for further evaluation. Third, there is a need to further investigate fine and ultrafine particles for residences, especially in rural areas, as direct burning is still a major source for cooking and heating in these areas. Only a small number of studies so far have been devoted to indoor/outdoor PM1.0 (or smaller) concentrations in Chinese residences. 3.3. Data on indoor VOCs A large body of evidences has shown that, expose to formaldehyde, benzene, toluene and other VOCs can pose both acute and chronic health effects on people, from odor, sensory irritation to cancer (WHO, 2010). Although humans, building materials, consumer products (e.g., air fresheners) (Nazaroff and Weschler, 2004), and outdoor sources can all emit VOCs in indoor air, building materials usually contribute the most (Missia et al., 2010). Modeling the VOC emissions to predict and control indoor concentrations and human exposure has been extensively developed, as reviewed by (Liu et al., 2013e; Zhang et al., 2016c). The process of solid building materials (e.g., natural or synthetic wood products) emitting VOCs is usually dominated by Fickian diffusion, while emissions from liquid materials (e.g., paint) follow two consecutive steps, i.e., evaporation and diffusion. Liquid material emissions are important in newly decorated residences because major VOC emissions usually last for weeks to a few months, while VOCs emitted from solid materials are of concerns for existing residences because the emissions process usually takes months or years (Ye et al., 2014a). Approximately 90% of the time, VOCs are emitted at quasi-steady state (Xiong et al., 2013b). Although emission modeling is well developed and material testing is rapidly growing, a national-scale material labeling scheme, such as (AgBB, 2015; ECA, 2013), has not been well established and put into practice yet (Liu et al., 2013c). Therefore, China has yet to officially provide a benchmark or build a VOC emissions database that allows consumers to consciously select materials. One more issue associated with VOC concentration and exposure prediction is that emissions modeling usually works well in a chamber study but does not work well on long-term in a real environment (Liang et al., 2014; Yu and Kim, 2012) due to the potential interferences of seasonal variations in airflow, temperature, humidity and indoor chemistry. A few factors can contribute to this inconsistency. First, almost all the models assume that indoor air is well-mixed, which is impossible in real residential spaces (Ye et al., 2014b). Second, although the effects of humidity on VOC emissions from various materials are not consistent (Huang et al., 2006; Huang et al., 2016; Xu and Zhang, 2011), the temperature effect on emissions is much clearer. For example, temperature increases usually increase the emissions for most VOCs (increasing diffusion and decreasing partition); moreover, temperature increases may also increase the initial emittable concentrations for compounds such as formaldehyde, further accelerating the emissions (Huang et al., 2015; Xiong and Zhang, 2010). Third, indoor chemistry also explains many changes to indoor VOC concentrations, primarily via gas phase and surface reactions (Weschler, 2011). Indoor chemistry is not only a primary determinant of short-lived, highly reactive species indoors but also a major source of SOAs or particles that stem from secondary pollutants (Weschler, 2011). Overall, long-term VOC concentrations could be difficult to predict; however, an overall decaying pattern over a long period of time should be expected. Table 6 summarizes data on typical indoor VOC concentrations for N2000 residential buildings that were and were not newly decorated


705

Table 6 Summarized data measured over the last 10 years of indoor formaldehyde concentrations in urban residential buildings that were and were not newly decorated in China. Reference

Location

Measured period


Room function

Time after decoration

Windows & doors status

Indoor concentrations, μg·m−3 Mean SD

(Wu et al., 2016a)

Nanchong

2012.01–2014.06 65 (549 samples)

Living room, kitchen, bedroom

(Chen et al., 2016)

Wuxi

Living room, bedroom

(Han et al., 2014)a

Nanyang

2009 84 2010 2011 2012 2013 2013.03–2013.11 154 (413 samples)

(Zheng et al., 2014)

Shanghai

2011.10–2012.11 84 (288 rooms)

Living room, study, bedroom

(Fang et al., 2014) (Xu et al., 2014)

Beijing Wuhan Xinxiang

2009.03–2009.05 48 78 2009–2011 22

Bedroom

(Lu et al., 2013)

Nanning

2010.07–2011.06 73


(Huang et al., 2013) (Guo et al., 2013)

Beijing

2008.07–2012.09 383

Not specified

Hangzhou

Lanzhou

(Liu et al., 2013b) (Tang et al., 2012) (Li et al., 2012)

Beijing

557 rooms 980 rooms 787 rooms 10 10 10 10 2009.11–2009.12 210

1999 bedrooms, 136 studies, and 189 living rooms

(Li et al., 2013a)

2007 2008 2009 2011.07–2011.12

2010.09–2011.06 96 (421 rooms) 2008–2010 100


(Qin et al., 2011) (Xue et al., 2011) (Han, 2011)

Shanghai Changsha

2008.04–2009.12 20 (112 rooms) 2008.11–2009.10 149 rooms 195 rooms 2008.07–2008.10 148 (625 rooms)

Living room, study, bedroom, kitchen Living room, study, bedroom

(Li et al., 2010)

Hangzhou

2007.01–2009.12 42

Not specified

(Wang et al., 2010b) (Zhai et al., 2010)

Chongqing

2008.07–2008.11 37 (178 samples) 2008–2009 186 (558 samples)


(Zhang et al., 2009)

Luoyang

(He et al., 2009)

(Liang et al.,

Chengdu Zhaoqing

Anyang

Shenyang


22 living rooms, 24 bedrooms, and 12 studies

Not specified

Living room, kitchen

Not specified

Living room, dining room, bedroom

Living room, kitchen, bedroom

Not specified

Zhuzhou

2008.03–2008.10 32 rooms 172 rooms 186 rooms 147 rooms Not specifiedc 73

Yangjiang

2008.01–2008.12 60 (180


Not specified

1 month 2 months 3 months 6 months 9 months 12 months ~3 months

Closed for 12 h prior 340 to test 440 280 140 120 90 Closed for 12 h prior 130 to test 60 60 60 70 b3 months Followed GB 405 3– 6 months 50325-2010 254 6– 12 months 139 12– 18 months 96 b 4 months Closed for 12 h prior 62 to test 4– 12 months 117 13– 24 months 61 25– 36 months 76 36– 44 months 55 N12 months Closed for 12 h prior 50 to test 260 b1 month Followed GB 96b 50325-2001 1– 2 months 86b 3– 5 months 62b 6– 9 months 57b Newly-decorated Closed for 12 h prior 119a to test b12 months Freely controlled by 131 occupants b12 months Closed 149 109 74 1– 3 months Closed 340 3– 6 months 210 6– 9 months 90 9– 12 months 70 b60 months Closed 28 N60 months 16 1– 6 months Followed GB/T 110 18883-2002 b1 month Closed for 12 h prior 172 N12 months to test 74 N24 months 60 1– 6 months Closed for 12 h prior 72b to test 1– 6 months Closed for 12 h prior 7– 24 months to test ~1 month Closed 290 ~3 months 240 ~6 months 210 ~12 months 110 N12 months 60 6– 12 months Closed for 12 h prior 150b to test b6 months Followed HJ/T 158 167-2004 b3 months Followed GB 106 3– 6 months 50325-2001 116 6– 12 months 97 12– 24 months 81 24– 36 months 57 b1 months Closed 80 2– 6 months 80 7– 12 months 80 N12 months 80 b3 months Closed for 4 h prior 264 4– 6 months to test 247 7– 12 months 163 N12 months 104 Blank house 65 Newly-decorated Closed for 24 h prior

Min Max

120 210 110 80 60 30 160 60 50 30 80

14 16 8 5 6 30 170

178 69 23 5 19d 50d 13d 34d 13d

586 441 339 234 75d 175d 88d 100d 75d

81 60 32 22 20

169 86 62 87 670

90 111 6 96 5 64 10 100 80 70 50 28 0.2 14 20

664 739 776 1500 1420 1330 1100 213 540

92 65 59 18

1900

10 10 30 40 60 40 20 10

450 310 960 890 830 230 140 1000

13

2

634

68 99 110 54 28

10 10 10 10 10 60 40 40 19

320 550 1620 350 180 680 540 410 200

ND

33,340

23 25 25 6 3

84 76 54 35 13

(continued on next page)

706


Table 6 (continued) Reference

2009) (Gu et al., 2008)

(Zhao et al., 2008) (Tong and Huang, 2008)

Location

Measured period

Sanmenxia

samples) 2007.01–2007.12 82

Shijiazhuang 2007.02–007.06 Wenzhou


39

2007.04–2007.05 50a (223 samples) 50 (38 samples)

a b c d

Room function


Not specified

Living room, bedroom Living room, study, bedroom

Storeroom

1– 3 months 4– 6 months 7– 9 months 10– 12 months 12– 60 months 3– 6 months 1– 3– 5– 1– 3– 5–

2 months 4 months 6 months 2 months 4 months 6 months


to test Followed GB/T 18883-2002


Min Max

310 200 240 420 230

80 50 50 80 50 10

Closed for 12 h prior to test Followed GB 440 50325-2001 336 91 1070 842 416

640 430 610 820 700 730

Data were recalculated by Ye et al. The median number was used instead; The measured date was not specified but was assumed to be after 2006 based on the publication and submission dates; P25 and P75 were used instead of the minimum and maximum values.

among 22 cities in China. Except for one study in which the measuring period was not specified, all the selected data were measured within the last 10 years. Most of the measurements followed the standards, e.g., GB/T 18883-2002 (AQSIQ et al., 2002), which usually require the tested room to be airtight (closed windows and doors) for 12 h prior to the test. The idea for the zero air change rate is to allow the gas phase pollutant to accumulate. Although this method intended to focus on indoor emission sources, indoor VOCs that brought indoors from outdoors are not excluded completely. In addition, most of the data were given in units of mg m−3 and were converted to μg m−3. According to Table 6, the measured formaldehyde concentration ranges within the first 3 months, 3–6 months and 6–12 months are 10 μg m−3–33.3 mg m−3, 10 μg m− 3–1420 μg m−3 and 10 μg m− 3– 1620 μg m− 3, respectively. Most of the formaldehyde concentration data measured within the first 6 months exceed the 30-minute average concentration guideline of 100 μg m− 3 provided by WHO (2010). 100 μg m−3 is also the national residential recommended threshold in China (AQSIQ et al., 2002). Among the measured concentrations, except for one study that reported results at extremely high concentrations of N33.3 mg m−3, most of the reported peak concentrations were between 200 μg m−3 and 400 μg m−3. However, it seems that the peak concentrations keep appearing even after the decoration has been done more than one year ago. Caution should be taken that the measurement results may not be able to be interpreted as human exposure level under regularly ventilated conditions, since most of the data were obtained after windows being closed for a certain time. However, it could be useful for predicting exposure during the night because many Chinese residents tend to close the windows while they sleep. One study indicates that nearly half of the residents in eight cities would close the windows during the night in summer (Li, 2011) (also see Table 13). Another distinct issue is that the formaldehyde mean concentrations would probably decrease to around or below 100 μg m−3 after approximately 6 months and would continue at this level for years. This observation coincides with a previous theoretical study (Ye et al., 2014a), which indicated that, in the light of the National Research Council (NRC) material emission database (which is Canadian VOC emissions database that consists of emissions data measured around the year 2000 and was provided by NRC Canada), emissions from solid materials deplete to quasi-steady state after 3–6 months under normal ventilation conditions. Two additional notes should be mentioned: First, it can be expected that the materials in the NRC database are not the ones in the Chinese market during the last ten years; however, the suggested conclusion that ~ 6 months is sufficient to reach the end of the unsteady state

emissions seems applicable. Second, because emissions from liquid materials (e.g., paint) usually deplete after days to weeks (Deng et al., 2016; Tichenor et al., 1993; Xiong et al., 2013a), most VOCs emitted within the first month after decoration are from liquid materials, and solid materials dominate the emissions after the liquid material VOCs have evaporated (after ~ a month). The effects of temperature on the indoor formaldehyde concentrations have also been reported in a few studies, e.g., (Li et al., 2013a; Wu et al., 2016a). The results are in agreement with theoretical work (Xiong et al., 2013b) that the formaldehyde concentrations can be elevated if the indoor temperature increases. The relationship between humidity and formaldehyde emissions was tested in a study (Li et al., 2013a) that suggested a positive correlation between increasing relative humidity and increasing formaldehyde concentrations; however, the theory behind this study is still unclear to date. Other factors, such as room functions and material selections, have also been disused in some studies, however, one should be careful to draw conclusions or correlations for indoor formaldehyde concentrations by room function or selection of one or a few types of materials. Because, on the one hand, the formaldehyde concentrations largely depend on the combined material loading (the ratio of total material area to the room volume) and material age, etc. The relationship between room functions and material selections (or material age) in dwellings is usually not clear. Therefore, it would be difficult to link room functions with formaldehyde concentrations directly. On the other hand, there are also many factors which can affect formaldehyde concentrations in indoor environment, such as ventilation condition and indoor chemistry. Table 7 summarizes data on typical indoor benzene concentrations and concentrations of its homologues for approximately 1000 residential buildings in nine cities in China. The concentration ranges measured for benzene and its homologues are mostly larger than those for formaldehyde listed in Table 6. The maximum concentrations reported exceed 89 mg m−3, 134 mg m−3 and 56 mg m−3 for benzene, toluene and xylene, while GB/T 18883-2002 sets the corresponding thresholds at 110 μg m−3, 200 μg m−3 and 200 μg m−3, respectively (AQSIQ et al., 2002). However, the minimum concentrations of all the chemicals remain low at 102 μg m−3 for most of the cases. One of the reasons for this result could be that the emissions of benzene and its homologues from liquid materials usually result in high peak concentrations and low concentrations during the evaporation period and the after-depletion period, respectively. Generally speaking, while the 23 cities listed in Tables 6 and 7 vary in economy, culture, environment and resources, the indoor VOC pollution seems to be similar for all of them. The long-term decaying trend also


follows mass transfer theories. However, there are still a few issues that need to be addressed. First, although building materials potentially contribute the majority of indoor VOCs, VOCs also have outdoor sources, e.g., traffic and industrial emissions (Stojić et al., 2015). More studies should focus on indoor/outdoor relationships of VOC concentrations and their impact on potential VOC exposure. Second, the extensively monitored VOCs in Chinese residences are formaldehyde, benzene, toluene and xylene. These chemicals are regulated by the national IAQ standard. Those VOCs that may also have adverse or even carcinogenic effects on humans but are not regulated by the standard can be widely overlooked by the public. For instance, trichloroethylene was categorized as group 1 (carcinogenic to humans) in 2014 by the International Agency for Research on Cancer (IARC, 2015), and emissions of trichloroethylene were detected from nearly 20% of the materials included in the NRC database (Won et al., 2005). It is also necessary to discuss the odor effect produced by the VOCs emitted from building materials. Unlike human bioeffluents, concentrations of many VOCs can accumulate higher than the odor thresholds and irritation concentrations in dwellings. Table 8 shows a few examples of indoor VOC concentrations that surpass the odor or irritation thresholds provided by (Ruth, 1986). According to Table 8, at least nine VOCs that were detected in urban residential buildings in China reach the odor threshold and can pose acute effects on occupants. By combining Tables 6 to 8, we can observe that the majority of the concentrations measured for formaldehyde,

707

benzene, toluene and xylene are lower than the low olfactory threshold, indicating that VOC emissions from building materials can be sensed by occupants. However, according to Table 8, the odor issue may not be very serious among residential buildings, and odor is expected to fade away as the VOC concentrations decrease over time. The combined sensory effects of multiple chemicals are very complex (Devos et al., 1990; Ruth, 1986) and may not be consistent with Table 8. Table 8 also shows that VOC concentrations can exceed irritation levels in some cases (mainly formaldehyde and toluene), suggesting that indoor VOCs can cause irritation to occupants in homes; therefore, ventilation is critical for reducing the VOC concentration in these circumstances. However, similar to odor issue, the irritation issue is also not ubiquitous and can be alleviated after a given time. 3.4. Data on indoor SVOCs As an emerging topic around the world, SVOC exposure and the related health effects have been attracting increasing attention in China. Additives, such as plasticizers in plastic products and flame retarders in various indoor materials, as well as consumer products (e.g., pesticides) and indoor burning activities (e.g., smoking and cooking) are typical indoor sources of SVOCs (Wang et al., 2010a). With the help of the mass transfer modeling framework for VOCs, the emission mechanism and exposure pattern of SVOCs have been rapidly developed (Little et al., 2012; Liu et al., 2016; Xu et al., 2010; Zhang

Table 7 Summarized data measured over the last 10 years of indoor benzene concentrations and the concentrations of its homologues for residential buildings in China. Reference

Location

Measured period

(Liang et al., 2014)

Beijing

(Fang et al., 2014) (Zheng et al., 2014)

Room function


Ventilation when test

Substance


Min

Max

2010.07–2011.12 1

Living room

Finished on 2010.06.06

Closed for 12 h prior to test

574 509 164 116 92 203

2009.03–2009.05 48

Bedroom

N1 year

Shanghai

2011.10–2012.11 84 (288 rooms)


b44 months

Closed for 12 h prior to test Closed for 12 h prior to test

146 116 42 29 27 35 11

13 16 ND 1 2 3

Beijing

Benzene Toluene Ethylbenzene p/m-Xylene o-Xylene Styrene Benzene

(Huang et al., 2013) (Liu et al., 2013b)

Beijing

2008.07–2012.09 379

Not specified

b1 year

Beijing

2009.11–2009.12 210

Living room, kitchen

Not specified

Freely controlled by occupants Closed

(Li et al., 2013b)

Shenzhen

2010.11–2011.11 30 (1800 samples)

Not specified

b1 year

Not specified

(Lu et al., 2013)

Nanning

2010.07–2011.06 73


Newly-decorated Closed for 12 h prior to test

(Han, 2011)b

Anyang

2008.07–2008.10 148 (625 rooms)

Living room, dining room, bedroom

1– 12 months

Closed

(Li et al., 2010)

Hangzhou

2007.01–2009.12 42

Not specified

6– 12 months


(Liang et al., 2009)

Yangjiang

2008.01–2008.12 60 (180 samples)


Newly-decorated Closed for 24 h prior to test

(Gu et al., 2008)

Sanmenxia

2007.01–2007.12 82

Not specified

1– 60 months

(Zhao et al., 2008)

Shijiazhuang 2007.02–2007.06 39

a b c


The data measured in the living room were used. Data were recalculated by Ye et al. The median number was used instead.


3– 6 months

Followed GB/T 18883-2002 Closed for 12 h prior to test

Benzene Toluene Xylene Benzene Benzene Toluene Xylene Benzene Toluene Xylene Benzene Toluene Xylene Benzene Toluene Xylene Benzene Toluene Xylene Benzene Toluene Xylene Benzene Toluene Xylene Benzene Toluene Xylene

11 b25 1195 b50 689 b100 283

17 a

9 33a 14a

46b 83b 133b 44 253 190 79c 140c 86c

16 8a 1 65a 1 7a 0.2 20 50 100 10 10 25 10 10 ND 59 46 35 130 220 660 20 210 260 25 50 100

48 553 151 8650 5200 6350 92 1400 150 210 1720 1620 190 570 190 89,520 134,110 56,420 560 790 1030 3740 1920

708


Table 8 Summarized data measured over the last 10 years of indoor VOC concentrations reaching odor or irritation thresholds (Ruth, 1986) in residential buildings in China. Chemical

Olfactory threshold −(low-high, μg·m−3)

Irritating conc. (μg·m−3)

Max. detected conc. (μg·m−3)

Location

Measuring period

Indoor conc. data reference

Acetaldehyde Benzene

2.0 × 10−1–4.1 × 103 4.5 × 103–2.7 × 105

9.0 × 104 9.0 × 106

Cyclohexanone Ethyl acetate Formaldehyde

4.8 × 102–4.0 × 105 2.0 × 101–6.7 × 105 1.5 × 103–7.4 × 104

1.0 × 105 3.5 × 105 1.5 × 103

β-myrcene Styrene Toluene Xylene

7.2 2.0 8.0 3.5

101 102–8.6 × 105 103–1.5 × 105 102–1.7 × 105

– 4.3 × 105 7.5 × 104 4.4 × 105

140 89,520 8650 508 57 33,340 1900 1620 1500 288 244 134,110 56,420 6350 1920 1620

Beijing Yangjiang Shenzhen Beijing Beijing Yangjiang Shanghai Shenzhen Lanzhou Beijing Beijing Yangjiang Yangjiang Shenzhen Shijiazhuang Anyang

2009.11–2009.12 2008.01–2008.12 2010.11–2011.11 2010.07–2011.12 2010.07–2011.12 2008.01–2008.12 2008.04–2009.12 2010.11–2011.11 2011.07–2011.12 2010.07–2011.12 2010.07–2011.12 2008.01–2008.12 2008.01–2008.12 2010.11–2011.11 2007.02–2007.06 2008.07–2008.10

(Liu et al., 2013b) (Liang et al., 2009) (Li et al., 2013b) (Liang et al., 2014) (Liang et al., 2014) (Liang et al., 2009) (Qin et al., 2011) (Li et al., 2013b) (Li et al., 2013a) (Liang et al., 2014) (Liang et al., 2014) (Liang et al., 2009) (Liang et al., 2009) (Li et al., 2013b) (Zhao et al., 2008) (Han, 2011)

× × × ×

et al., 2016c). Unlike internally controlled VOC emissions, SVOC emissions are inherently an externally controlled process (Liu et al., 2013e). Therefore, SVOCs usually partition strongly onto interior surfaces, indoor particles or dust, while only a small portion of the molecules remain in the gas phase. This phenomenon has two implications on the indoor environment. First, using ventilation as a basic means to dilute gas phase SVOCs is almost completely ineffective. Compared to the gas phase concentration, the material phase concentrations in either the emissions source or other surfaces (acting as sinks) could be 3 to 10 orders of magnitudes higher (Xu et al., 2010). However, the partition characteristic with particles can have profound impacts on the combined indoor exposure to both particles and SVOCs in China (Liu et al., 2015) simply because particulate matter pollution can prevail in both indoor and outdoor environments in many parts of the country. This bonding effect also makes SVOCs a multi-risk pollutant that has three simultaneous pathways for exposure, i.e., inhalation, dermal and oral. All three pathways could be important for SVOC exposure (Wang et al., 2014b). Alarmingly, the primary exposure pathway to SVOCs in normal indoor environment is probably by ingestion of dust, followed by particle inhalation, dermal absorption and air inhalation (Little et al., 2012). This estimation further confirms that dilution of gas-phase SVOCs would be much less effective in terms of reducing health effects on occupants compared to the removal of particles both in dust or gas-phase. Second, the on-site measurement of SVOCs is a difficult task. Gas phase concentrations can be too low to have meaningful results, so dust, particle or skin surface concentration measurements become the primary method for predicting SVOC concentrations in the gas or particle phase (Gong et al., 2014a; Wu et al., 2016b). Going a step further, SVOC exposure and intake can be estimated by measuring the SVOC concentrations in human urine (Gong et al., 2015; Guo et al., 2011). To date, relevant studies on indoor SVOC concentrations are still rare. Table 9 summarizes the available literature on field studies of the concentrations of phthalates, which are a group in the SVOC family that is widely used as plasticizers, in N300 Chinese dwellings among 11 cities. The evidence shows that the detection frequencies of some phthalates, such as DBP, DEP and DMP, are very high, while DEHP is basically ubiquitous, suggesting a widespread of SVOC exposure risk for Chinese people. Typically, the mean concentrations of the detected total PAEs range from 100 to 101 μg m−3 in both the gas and particle phases, while the concentration range can be between 102 and 103 μg g−1 in dust. Because phthalates or other SVOCs mostly originate from indoor sources or are brought indoors by particles or dust, the concentration differences in residential buildings are less significant for different cities compared to the differences between multiple media. Therefore, by keeping a clean home with little settled dust and few

airborne particles, human exposure to indoor phthalates or other SVOCs can be effectively reduced. 3.5. Data on indoor moisture/mold Humans and their activities indoors are usually main sources of moisture indoors and moisture can be also brought indoors by infiltration or ventilation systems. Although moisture should not be considered as a pollutant, the moisture content in the air (relative humidity, RH) is an important agent modifying human exposures in indoor environment, including dwellings (Wouter Borsboom et al., 2016). Either too low or too high levels of humidity can cause problems in homes. On one hand, low humidity environment (RH b 30%) is usually associated with sensory discomfort, e.g., skin dryness, irritation and so forth (Reinikainen and Jaakkola, 2003; Toftum et al., 1998a; Toftum et al., 1998b). On the other hand, high humidity may affect the perceptibility of air quality (Fang et al., 1998), triggering the growth of mold, and leading to more serious health effects, such as allergies (Adams et al., 2016; Bornehag et al., 2004a; Bornehag et al., 2004b; Fisk et al., 2007; Jaakkola et al., 2002). Surprisingly, although studies on mass and moisture transfer between building insulation and indoor/outdoor environment have been continuously developed (Zhang et al., 2016b), systematic field investigations on indoor humidity in China, especially in dwellings, are still limited. One available and valuable example is a measurement study performed by (Zhang and Yoshino, 2010) on indoor humidity environment in the dwellings of nine Chinese cities (86 dwellings in total), the results indicate that serious problems of high or low humidity generally exist. According to this study, indoor RH can be lower than 20% in northern China mainly due to over-drying the indoor air by district heating, however, indoor RH can also reach 80% in Chongqing and other southern cities with inadequate heating and high outside absolute humidity. During summer, the absolute humidity can go beyond the maximum acceptable humidity value (absolute humidity: 12 g/kg) recommended by ASHRAE (2013). Although the data from this study is mainly from 2001 to 2004, the major reasons behind those findings, i.e., district heating or not, humid local climate or not, have not been changed much. Thus, it is reasonable to believe the findings are still applicable and can be adopted. The available studies on indoor dampness and mold in residential buildings in China are also rare. It is not until recently that microbiomes in buildings started to attract attention. Table 10 summarizes the available literature on field investigation of indoor mold growth in N500 Chinese dwellings in Shanghai. In addition, since indoor airborne fungus is a bio-indicator of indoor air quality whose concentration appears to be associated with indoor moisture-related problems (Wang et al., 2016b), airborne culturable fungi in the unit of cfu m−3 (colony forming units (CFU) is often used to quantify microbes in indoor air) is also

Table 9 Summarized data measured over the last 10 years of phthalate concentrations on multiple media for urban residential buildings in China. Location

Measured period


Room function

Medium (unit)

(Bu et al., 2016)

Chongqing

2014.11–2015.02

30

Living room

Not specified Not specified

Gas (μg·m−3) Dust (μg g−1) Gas (μg m−3) Dust (μg g−1) PM2.5 (ng m−3) PM10 (ng m−3) Gas (μg m−3) Particle (μg m−3) Dust (μg g−1) Gas (μg/m−3) Particle (μg m−3) Gas (μg m−3) Particle (μg m3) Gas (μg m−3) Particle (μg m−3) Dust (μg g−1) Dust (μg g−1)

Not specified

Dust (μg g−1)

Bedroom

(Zhang et al., 2014a)

Tianjin

2010.12–2011.06

13

Living room

(Wang et al., 2014b)

Xi'an

2012.09–2013.01

14a

Not specified

(Pei et al., 2013)

Hangzhou

2011–2012

10

Living room

Bedroom

Study

(Zhang et al., 2013a) (Guo and Kannan, 2011)c

(Lin et al., 2009)d

Nanjing

2011.03–2011.06

215

Beijing

2010.05–2010.06

11

Shanghai

21

Guangzhou

11

Urumchi

7

Jinan

13

Qiqihar

12

Beijing

2008.05

10

Concentrations, mean (min, max) BBP

BBzP

DBP

ND (ND, 0.02) 0.2 (ND, 2.8) 0.01 (ND, 0.18) 0.8 (ND, 10.9) 0.32 (0.01, 4.8) 0.63 (0.01, 8.0)

130.7 (5.7, 1132.1) 318.4 (7.3, 1466.2)

2.7 (ND, 3.7) 2.0 (ND, 3.5) 1.4 (ND, 1.5) 1.7 (0.68, 2.2) 2.1 (ND, 3.1) 2.0 (0.47, 2.4) 2.9 (ND, 38.7) 0.6b (0.1, 1.1) 0.2b (0.1, 12.0) 0.1b (ND, 0.1) 0.2b (0.2, 0.6) 0.2b (ND, 7.4) 0.4b (0.2, 1.2) 39

0.74 (0.35, 1.1) 1.2 (0.54, 2.0) 1.0 (0.54, 1.5) 1.1 (0.48, 1.7) 0.87 (0.40, 1.5) 0.95 (ND, 1.3) 52.3 (ND, 2150) 18.9b (7.0, 31.5) 11.6b (9.2, 58.7) 9.3b (2.3, 128) 21.9b (10.9, 147) 26.9b (1.5, 96.2) 170b (77.9, 1160) 39

DEHP

DEP

DiBP

DMP

DnBP

0.35 (0.11, 1.4) 2353 (279, 7424) 0.38 (0.07, 1.1) 1892 (121.8, 7958) 44.36 (0.87, 179.8) 92.30 (2.62, 304.9) 0.47 (0.05, 1.9) 1.0 (0.09, 4.2) 798.6 (67.1, 3475) 1.2 (0.03, 1.3) 1.7 (0.28, 3.5) 1.3 (0.30, 2.1) 0.72 (0.56, 9.0) 0.87 (0.25, 1.3) 1.6 (0.60, 3.9) 462 (0.3, 9950) 156b (47.6, 883) 146b (56.6, 949) 98.2b (9.9, 252) 348b (149, 939) 319b (117, 1380) 563b (204, 8400) 1606

0.17 (0.08, 0.44) 14.6 (0.7, 91.3) 0.17 (0.07, 0.45) 16.0 (0.2, 99.4) 0.75 (0.07, 4.5) 1.6 (0.08, 7.4)

0.58 (ND, 1.9) 146.9 (8.9 1029) 0.54 (ND, 1.8) 181.6 (4.8, 842.0)

0.90 (0.37, 1.6) 4.9 (ND, 25.3) 0.87 (0.2, 1.6) 6.0 (ND, 32.0) 3.0 (0.19, 24.3) 9.0 (0.25, 47.5) 0.51 (ND, 2.5) 0.10 (ND, 1.8) 5.7 (ND, 68.8) 3.7 (0.43, 5.3) 0.80 (0.28, 1.3) 0.92 (ND, 6.6) 0.23 (ND, 0.70) 0.80 (0.24, 2.2) 0.15 (ND, 0.56) 0.4 (ND, 24.0) 0.7b (ND, 1.6) 0.3b (0.2, 0.9) 0.06b (ND, 0.7) 0.1b (0.1, 0.3) 0.2b (0.1, 0.8) 0.5b (0.3, 8.2) 18

0.38 (ND, 0.02) 228.4 (24.7, 1087) 0.36 (ND, 1.7) 180.0 (33.6, 493.5)

1.0 (ND, 6.2) 1.6 (ND, 8.0) 901.0 (ND, 7228) 2.7 (0.73, 4.8) 0.62 (0.21, 0.85) 0.90 (0.48, 4.8) 0.55 (0.14, 0.86) 1.8 (0.48, 2.9) 0.22 (ND, 0.42) 0.9 (ND, 33.9) 0.4b (0.1, 0.6) 0.2b (0.2, 0.8) 0.1b (ND, 0.3) 1.5b (0.8, 6.1) 0.4b (ND, 45.5) 0.8b (0.3, 1.0) 20

12.6b (7.2, 83.2) 11.1b (4.5, 63.9) 10.4b (2.6, 19.7) 26.0b (13.2, 299) 33.6b (7.0, 85.9) 32.8 2 (6.5, 87.9)

DOP

∑PAEs

0.10 (ND, 0.78) 0.206 (ND, 2.6)

179.2 (7.3, 1244.2) 422.1 (13.9, 1591.3) 2.6 (0.20, 8.3) 3.8 (0.09, 14.8) 2153 (122.9, 9504) 11.0 (1.5, 16.1) 6.3 (1.3, 11.0) 5.5 (1.3, 16.6) 4.2 (1.9, 14.5) 6.5 (1.4, 11.1) 4.9 (1.1, 8.5) 520 (0.9, 10,900) 255b (63, 930) 173b (75.6, 1080) 151b (24, 303) 428b (180, 1040) 401b (204, 1540) 765b (450, 8590)

0.59 (ND, 2.2) 1.1 (ND, 4.9) 447.8 (3.6, 4357)

1.6 (ND, 39.5)

709

Note: BBP: butylbenzyl phthalate; BBzP: butyl benzyl phthalate; DBP: dibutyl phthalate; DEHP: di(2-ethylhexyl) phthalate; DEP: diethyl phthalate; DiBP: di(isobutyl) phthalate, DMP: dimethyl phthalate; DnBP: di(nbutyl) phthalate; DOP: dioctyl phthalate; PAEs: phthalate esters. a The data were resulting from the measurements for 14 residences and 14 office buildings with basic interior decoration and common indoor materials. b Median number was used instead. c Three more phthalates, i.e., di-n-hexyl phthalate (DnHP), dicyclohexyl phthalate (DCHP) and di-n-octyl phthalate (DnOP), were also measured/detected but not included in this review. d DCHP was also measured/detected but not included in this review.


Reference

710


Table 10 Summarized data investigated/measured over the last 10 years of visible mold growth and airborne culturable fungi in urban residential buildings in China. Reference

Location

Measured period


Room function

(Wang et al., 2016b)

Shanghai

2013.03–2014.12

454

Child's bedroom Living room

(Wei et al., 2016)

Shanghai

2014.06–2014.11

71

(Hao, 2015) (Liu et al., 2014)

Hangzhou Xi'an

2014.04–2015.01 2012.03–2012.04

60 24

(Fang et al., 2013) (Sun et al., 2011)

Beijing Langfang

2009.11–2010.10 2007.12–2008.03; 2009.07–2009.08

31 10

Living room, bedroom, kitchen Not specified Reference homea Case homea Not specified Living room

Shaoguan


Visible mold growth

Airborne culturable fungi, cfu·m−3 Mean

SD

Min

Max

313 288

6 19

3184 3044

Freely controlled by occupants Freely controlled by occupants Not specified Closed

376: inside surface of exterior wall 332: ceiling surface 40 residences

310 300

Not visible Not specified

Not specified Closed

Not visible Not specified

653 454 674 837 1409 492 1909 1369

10

68 168 606 241 470 667

240 2752 389b 514b 456b 876b 62 3498 (Winter) (Summer) (Winter) (Summer)

a Homes with children with a prevalence of asthma, pneumonia and dry cough were determined as the case homes, while reference homes have similar location, building construction with healthy children; b P5 and P95 were used instead of the minimum and maximum values.

summarized in Table 10 based on measurement data in another five cities, as references to show typical occupant exposure to indoor microbes. As shown in Table 10, visible mold growth seems to be a common issue in Shanghai, as Shanghai can be considered as a humid city in the area of hot summer and cold winter climate zone. In the meanwhile, household airborne culturable fungi concentrations in most of the residences appear to be acceptable, with the concentration ranging from 6 cfu m−3 to 3498 cfu m−3 and the mean concentrations are around 300 cfu m−3 to 800 cfu m−3. The 20 residences measured in Langfang and Shaoguan are exceptions, where the mean concentrations of airborne culturable fungi both exceed 1400 cfu m−3 in winter. And the reasons to this high concentration of fungi can be due to little ventilation in dwellings in Northern cities (such as Langfang) with district heating and high levels of humidity in dwellings in Southern cities (with no district heating, such as Shaoguan). 3.6. Data on indoor/outdoor inorganic compounds Another category of indoor pollutants that can lead to acute or chronic symptoms in occupants are inorganic compounds, typically encompassing carbon monoxide (CO), ozone (O3), nitrogen dioxide (NO2), sulfur dioxide (SO2), ammonia (NH3), etc. (WHO, 2006; WHO, 2010). However, the indoor and outdoor sources for these compounds are varied. First, emissions of NO2 from natural sources far outweigh those generated by human activities at a global scale (WHO, 2006), suggesting that outdoor NO2 concentration would be of interest. Second, ozone is primarily resulting from the photochemical process in the atmosphere. In residential context, although there are indoor sources of O3, indoor O3 has been primarily transported from outdoors (Weschler, 2000). Third, with regards to CO and SO2, the major indoor source, for CO, SO2 and many other organic compounds, is combustion using fossil fuels or biofuels for heating, cooking, environmental tobacco smoking and other human activities. Also, both have outdoor source origins, such as transportation and power generation (WHO, 2006; WHO, 2010). Forth, similar to VOCs, additives to building materials (e.g., concretes) are typical indoor sources of ammonia, making NH3 a majorly indoor originated pollutant (Bai et al., 2006; Tomoto et al., 2009). Tables 11 summarizes the published data on indoor CO, O3, NO2, SO2 and NH3 concentrations for nearly 500 dwellings in total among five cities in China. Some of the data were given in units of mg m−3 and were converted to μg m−3. At present, systematic studies on typical indoor inorganic pollutants in residential buildings in China are still lacking, however, available data indicate that indoor pollution caused by inorganic gases can be generally common. The reported maximum concentration

for each of the above five gases exceeds the concentration recommendation provided by GB/T 18883-2002 at 500 μg m− 3, 240 μg m−3, 10,000 μg m− 3, 160 μg m−3, 200 μg m−3, respectively, for SO2, NO2, CO, O3 and NH3. As a comparison, Table 12 summarizes the official ambient air quality data with regards to SO2, NO2, CO and O3 for 31 cities (provincial capitals and municipalities in mainland China) in 2014 (NBS and MEP, 2015). It can be found that the annual average concentrations for both SO2 and NO2 obtained from all the above cities are below 100 μg m−3, indicating that outdoor pollution of SO2 and NO2 may not be serious throughout the year. The 95th percentile daily maximum 8-hour average concentrations for CO are also below 5000 μg m−3, which is half of the value compared to the indoor recommendation provided by GB/T 18883-2002. On the other hand, the 95th percentile daily maximum 8-hour average concentration of O3 surpasses 160 μg m− 3 for seven cities (e.g., Beijing) in Table 12. In other words, possible indoor O3 pollution can occur 5% of the days annually for these cities. Furthermore, the data in Tables 11 and 12 suggest that extreme indoor SO2, NO2 and CO pollution can be due to emission sources indoors, and outdoor O3 concentration should be of concern at a higher level. 3.7. Data on indoor radon Radon usually occurs naturally as a decay product of radium from soil and construction materials and enters into indoor environment (Feng and Lu, 2016; Li et al., 2006). It is classified as a human carcinogen (Group I) by The International Agency for Research on Cancer (IARC, 2015). There is direct evidence from residential epidemiological studies of the lung cancer risk from radon and the exposure-response relationship is best described as being linear, without a threshold (WHO, 2010). Among radon'’s isotopes, 222Rn is a radioactive extremely inert gas and has the relatively longest half-life (~ 3.8 days). 222Rn and its progeny are present in all dwellings and usually have significant impact on indoor environment (Feng and Lu, 2016). Table 13 summarizes data on indoor radon (222Rn) concentrations for both urban and rural residential buildings in N 30 cities in China. The data were all measured within the past 10 years and given in the unit of Bq m−3. Many systematic studies have been conducted during that time. Except for one study, which use activated carbon to measure radon for a few days (Mei et al., 2016), most the studies use other techniques, e.g., solid state nuclear track detectors, to measure radon for a long term and report the radon concentration in a time-averaged fashion. The majority of data reported in Table 13 are grouped by building age. The maximum reported radon concentration that exceeds


711

Table 11 Summarized data measured over the last 10 years of indoor inorganic pollutant concentrations for urban residential buildings in China. Reference

Location

Measured period


Room function


Gas

(Yang, 2015)

Xi'an

2014.04

20


O3

(Lu et al., 2013)

Nanning

2010.07–2011.06

73

(Liu et al., 2011a)

Beijing

2010.12

100

Living room Kitchen Toilet Primary bedroom Secondary bedroom Living room, study, bedroom Bedroom

(Zheng et al., 2011)

Beijing

2010.01–2010.04

60

Bedroom

Closed for 12 h prior to test Follow GB/T 18204.23-2000 Freely controlled by occupants

(Wu et al., 2010)

Shanghai

2007.09–2007.10

50 49 49 49 109 113 110 109 113 110

Reference homec Case homec Reference homec Case homec Not specified

2008.02–2008.03 (Wang et al., 2008)

Lanzhou

2006.11–2007.02

2007.05–2007.09

a b c d

Not specified

Followed GB/T 18883-2002

Indoor concentrations, μg·m−3 Mean

Min

Max

NH3

120 190 90 70 180 339a

80 150 60 40 150 75

150 250 130 100 240 2530

CO

12,680b

600

71,700

NH3 NO2 CO NO2

80 40 900 58 67 72 78 460 470 6480 250 170 2510

30 10 500 41d 45d 48d 50d 70 80 5360 20 20 1190

220 300 5300 74d 78d 134d 128d 3240 4170 15,600 1930 360 6590

SO2 NO2 CO SO2 NO2 CO

SD

50 40 600

Data were recalculated by Ye et al. The data were calculated based on multiple datasets and may not be as rigorous as the actual mean value. Homes with a child that has asthma were determined as the case homes, while homes with a healthy child were taken as reference homes. P25 and P90 were used instead of the minimum and maximum values.

500 Bq m−3 is found in a newly-built dwelling. However, this peak concentration is measured by closing windows for 24 h and radon can be therefore more easily accumulated in indoor air. Besides that, the radon concentration ranges for building built before 1980, 1980s, 1990s and after 2000 are 7 Bq m− 3 to 107 Bq m−3, 6 Bq m− 3 to 200 Bq m−3, 1.9 Bq m−3 to 167.6 Bq m− 3 and 5 Bq m− 3 to 238 Bq m−3 under normal ventilation. It can be found that the radon concentrations would be reduced over time in general. Considering that the radon annual-averaged concentration recommended by GB/T 18883-2002 is 400 Bq m−3, the indoor radon pollution in Chinese dwelling is reasonably acceptable overall. And normally no special actions need to be taken when radon concentration level is below 400 Bq m− 3 (whether the criterion is low enough is another topic). This is important because it would be much more difficult to get rid of radon once it is measured in high concentrations in indoor environment, compare to methods to reduce other pollutants, e.g., reducing indoor particles using an air cleaner.

3.8. Data on effects of human behavior on indoor air pollution Another topic associated with indoor pollutant emission, concentration and exposure is occupant behavior. It should be noted that recent occupant behavior studies partially resulted from the need to improve the performance of building energy simulations (Yan et al., 2015). As more studies have been conducted on occupancy and equipment use monitoring for building energy modeling or adaptive occupant behavior studies, the effects of occupant behavior on indoor pollutant exposure can be extracted. However, the majority of the studies on occupant behavior and indoor air pollution are related to particulate matter. Table 14 outlines available studies on window opening behavior monitoring and the effects on the exposure to indoor particulate matter in residents among 12 cities across three climate zones in China. Questionnaires, interviews, on-site monitoring, and mathematical models have all been used to study occupant behavior, and all the outcomes can be considered as either explicitly or implicitly related to

Table 12 Ambient air quality with regards to SO2, NO2, CO and O3 for 31 cities (provincial capitals and municipalities in mainland China) in 2014 (NBS and MEP, 2015). Annual average concentrations were given for both SO2 and NO2, while 95th percentile daily maximum 8-h average concentrations were given for both CO and O3. The data were given in units of mg·m−3 for CO and were converted to μg·m−3. City

SO2 (μg·m−3)

NO2 (μg·m−3)

CO (μg·m−3)

O3 (μg·m−3)

City

SO2 (μg·m−3)

NO2 (μg·m−3)

CO (μg·m−3)

O3 (μg·m−3)

Shijiazhuang Zhengzhou Jinan Beijing Tianjin Hefei Wuhan Xi'an Chengdu Shenyang Nanjing Changsha Harbin Taiyuan Changchun Chongqing

62 43 73 22 49 23 21 32 19 82 25 24 57 73 41 24

53 51 47 57 54 31 55 47 59 52 54 42 52 36 47 39

4200 3100 2200 3200 2900 1600 1800 3000 2000 2000 1600 1800 1600 3200 1500 1800

161 116 184 200 157 69 156 128 147 165 183 117 111 125 132 146

Hangzhou Xining Urumqi Lanzhou Yinchuan Shanghai Nanchang Guangzhou Nanning Guiyang Hohhot Kunming Fuzhou Lhasa Haikou

21 41 25 29 69 18 25 17 15 24 50 20 8 10 6

50 38 56 48 42 45 33 48 37 31 44 36 36 20 16

1300 2500 3400 2700 2400 1300 1600 1500 1600 1300 4000 1500 1300 1800 900

169 89 109 108 124 149 129 165 126 103 117 111 137 134 102

712


Table 13 Summarized data measured over the last 10 years of indoor radon (222Rn) concentrations for urban and rural residential buildings in China. Reference

Location

Measured period


2015–2016

(Wu et al., 2014)

13 cities in Jiangsu Province


(Xu et al., 2013)

Chengdu

2012.02–2012.07 31 248 492 2009.01–2009.12 100

Living room, study

Freely controlled by occupants

(Zhang and Dai, 2012) (Xu et al., 2011)

Xuzhou

2008.11–2009.02 75

Not specified

Xiamen

2008.03–2010.12 15


Freely controlled by occupants Freely controlled by occupants

(Xiao et al., 2011)

Hengyang

2008.03–2008.05 46 2009.03–2009.05

Living room, bedroom, kitchen


(Hu et al., 2011)

10 cities in Zhejiang Province

Bedroom, living room


(Lan et al., 2010)

Guangzhou

2007.03–2008.12 46 samples 129 samples 99 samples 2008.10–2010.04 135 samples

Not specified


(Su et al., 2010)

Urumqi

Not specified


(Zhou et al., 2010)

Shijiazhuang

2008.08–2009.08 2 samples 28 samples 9 samples 44 samples 2007.04–2007.06 95

Bedroom


(Lu et al., 2010)

Suzhou

2009.03–2010.03 150

Bedroom


(Zhuo et al., 2010)b

Xinyang Kunshan Xiamen Zhuji Shenzhen Qinghai Shanghai

2008.08–2010.03 52 30 66 40 142 50 2007.05–2008.06 12 samples 5 samples 11 samples 34 samples 78 samples 67 samples 2006.12–2007.3 332 samples

Not specified


Not specified


Not specified


(Gao et al., 2009a)

Tianjin

Not specified


(Mei et al., 2016) Guangzhou

(Zhao, 2009)

1796 samples

Room function

Closed for 24 h prior to test Freely controlled by occupants

Built year

Indoor concentrations, Bq·m−3 Mean SD

Min

Newly built

84.2

12.1 524.6

b1980 1980s–1990s N2000 1980s 1990s N2000 Not specified

23 32 31 27.1 38.6 41.0 42

10 30 27 12.3 24.6 22.4

7 6 5 8.4 8.8 12.1 14

49 200 238 57.3 167.6 177.1 170

b1970 1980s 1990s N2000 1950s–1960s 1970s–1980s 1990s N2000 1980s 1990s N2000 b1980 1990s N2000 b1960 1980s 1990s N2000 b1980 1980s–1990s N2000 b1910 1980s 1990s N000 Not specified

19.8 26.0 21.0 30.7 58 47 42 42 26.9 27.3 31.2 30.2 41.1 34.6 60.0 66.5 47.0 49.8 30.9a 28.1a 40.2a 15.3 33.4 30.2 32.8 30.7 26.7 32.5 29.8 43.1 67.1 20.1 18.8 26.7 24.5 22.2 30.7 30.8

7.5 4.5 5.8 9.2 26 31 15 12

12 20 8 17 34 11 12 23 11.4 1.9 5.0 4

28 30 28 56 107 87 65 73 79.1 90.7 161.3 156

33.9 46.5 28.6 20.6

36 19 26 22 16.3 9.3 13.9 3.4

84 132 105 90 61.0 79.6 111.0 147.6

18.0 25.5 13.8 13.8 17.3 41.8 11.2 4.3 12.3 17.1 10.0 18.3

10 4 5 12 6 18 7 13 11 10 6 12 7.0

128 116 76 71 129 203 44 23 51 95 60 87 232.6

b1960 1960s 1970s 1980s 1990s N2000 Not specified

Max

a

Data were recalculated by Ye et al This study also includes measurements in Guangzhou, Urumqi and Xuzhou, however, the data recorded in these three cities have been published in separated papers and included in Table 13 as well. b

the potential exposure to particulate matter in urban residential buildings. According to Table 14, the link between occupant behavior and indoor particle exposure has been preliminarily addressed, and a few conclusions can be summarized. First, the occupant behavior on window opening is strongly related to indoor thermal comfort adjustment and personal habits (e.g., opening windows in the morning); these habit are usually lifelong (Chen et al., 2013). Therefore, window opening behavior and the consequent particle exposure pattern in a naturally ventilated dwelling are very different from those in an air-conditioned dwelling. Reducing the impacts of opening windows on the exposure to high concentrations of outdoor particles is a long-term effort. Second, improving the airtightness of windows and using air cleaners can be practical solutions for improving IAQ in dwellings under haze

conditions (Ma et al., 2016; Wang et al., 2015a). However, simply closing windows as an anti-haze solution would be ineffective, partially due to particle penetration (Gao et al., 2014). The studies on effects of human behavior, besides cooking, on indoor VOC, SVOC, mold and other inorganic gas concentration and exposure in residential context are still scarce. However, a few more examples can be further discussed as well. First, the use of cleaning products and air fresheners. Using cleaning products and air fresheners in buildings, including residents, to promote hygiene, aesthetics, and material preservation is another major human activity indoors. Many volatile organic compounds can be emitted to indoor air, and ozone-initiated reactions can also generate secondary emissions (Nazaroff and Weschler, 2004). The peak concentrations of the emitted substances from cleaning agents could be as much as

Table 14 Summarized studies on the relationship between window opening behavior and potential exposure to indoor particulate matter. Reference

Research method

Location & climate zone

Measuring period

Major outcomes by the original authors

Comments by Ye et al.

Implicitly related to exposure to particles

(Chen et al., 2015)

Conducted a survey including 73 families to verify statistical analysis of occupant behavior, one family was monitored closely 642 and 838 individuals took part in the winter and summer survey, respectively, and obtained over 2000 questionnaires Proposed 3 categories to quantitatively describe human behavior, i.e., time related, environmental related and random, and tested in a residential building Measured CO2 and CO concentrations along with a window opening behavior survey in 5 apartments Obtained 939 questionnaires through a survey conducted in 8 cities, i.e., Chongqing, Shanghai, Chengdu, Wuhan, Nanjing, Suzhou, Ningbo, Changsha, Nanchang

Changsha: hot summer and cold winter

Not specified

The probability of air conditioner or heater usage reaches a peak in the afternoon in summer and winter, respectively

Windows are more likely to be opened in the morning for occupants to exposure to more outdoor particles

Hangzhou: hot summer and cold winter

2010.3, 2010.8

Elderly residents exhibit a more frugal behavior pattern than the younger ones in terms of heating and cooling

Beijing: cold

Summer in 2010 and winter in 2011

Once the weather conditions are suitable, window opening actions usually can be categorized as time related mode

Indicating that elderly residents are more likely to utilize natural ventilation and therefore expose to particles in outdoor air more frequently Since habits usually last life long, the exposure pattern could be predicted

Beijing: cold

2010.4–2010.5

CO2 can be a good predictor of the window opening behavior for occupants

All 8 cities: hot summer and cold winter

2007–2008

In summer, N90% and 50% of the residents would open window in the morning or during the night, respectively, to take advantage of free cooling; In winter, 3/4 of the residents would use window ventilation for thermal comfort and dehumidification, Develop a stochastic model that takes outdoor air quality into account, however, outdoor temperature is still the most important explanatory variable affecting occupants' interactions with windows Improving indoor air quality, i.e., reducing PM2.5 and CO2 concentrations, could be achieved by combining window ventilation and air cleaners under various haze conditions The correlation between indoor and outdoor PM2.5 concentrations is affected by airtightness of the building envelope (e.g., windows)

(Chen et al., 2013)

(Peng et al., 2012)

(Jian et al., 2011)

(Li, 2011)

Explicitly related to exposure to particles

Since CO2 is an indicator for bioeffluents, odor can also be a window opening stimulus, and potentially affects occupants' exposure to particles indoors It should be noted that outdoor PM2.5 concentrations would be potentially higher both in the morning and in the evening than that of in the afternoon due to peak traffic emissions

(Shi and Zhao, 2016)

Monitored five and three naturally ventilated residential apartments in Beijing and Nanjing, respectively

Beijing: cold Nanjing: hot summer and cold winter

2013.10–2014.12

(Ma et al., 2016)

Developed a model to utilize window ventilation and air cleaners under haze condition and tested in a dormitory

Beijing: cold

Not specified

(Wang et al., 2015a)

Measured indoor and outdoor PM2.5 concentrations in two rooms with all windows closed and no heating and air-conditioning Measured indoor and outdoor PM1, PM2.5 and PM10 concentrations in a residential building with all windows closed and no heating and air-conditioning Interviewed 500 residents

Beijing: cold

2014.6, 2015.6

Shanghai: hot summer and cold winter

2012.12

I/O b 1 and correlation between indoor and outdoor PM1 (and PM2.5) concentrations is more obvious than that of PM10

PM1 and PM2.5 can be easily penetrated through window slits and thus closing windows is not an effective solution to isolate particles from outside

Shenyang: severe cold

2012.1

Subjective feeling of indoor air quality and personal health consciousness were found to be significantly correlated with opening window habit

Shenyang is a northern city that usually suffers severe haze weather in winter, it is reasonable to see residents are cautious about opening windows to expose to outdoor air more directly

(Gao et al., 2014)

(Huang et al., 2014)

Residents are potentially exposed to outdoor air pollutants when using window ventilation to adjust thermal comfort

It is practical to improve indoor air quality in residential buildings under haze condition by using air cleaners


Relevance

Improve windows airtightness is important for residential buildings because at present, positive pressure would be hard to achieve and maintain for residential buildings

713

714


hundreds to thousands milligram per cubic meters, which are almost at the same order of magnitude as what the emission of a new building material source can cause at its peak (Little et al., 1994; Nazaroff and Weschler, 2004; Singer et al., 2006). However, the pollutants emitted from cleaning agents usually behave as pulses, and the primary and secondary emissions of a cleaning product could last only for hours under normal ventilation. Second, the use of fragrances and scented products. Indoor spray, diffusers, candle, evaporators and other scented products are starting to get attention in China. Questions in regard to a possible impairment of indoor air quality also arise (Uhde and Schulz, 2015). Unlike cleaning agents, the emissions from many fragrances and scented products usually last longer time. The total body of relevant studies is still small, however, according to (Uhde and Schulz, 2015), emission rates are determined to exceed 2000 μg unit−1 h−1 for five commonly used solvents. In addition, a majority of the compounds used in scented products are reactive enough to be susceptible to indoor chemistry, (Nazaroff and Weschler, 2004; Singer et al., 2006; Uhde and Salthammer, 2007), which means the cocktail of indoor air pollutant mixture can be further affected. Third, the selection of furniture materials. As partially implied in Section 3.3, the selection of materials would have impacts on the types and concentrations of VOCs emitted to air indoors. Both composition and concentration of VOCs can vary among different materials, depending on the raw materials and manufacturing process. Both natural and synthetic materials can emit compounds at harmful levels (Won et al., 2005; Ye et al., 2014c). Even though an overall decaying pattern for long-term emissions of VOCs from building materials can be expected (Ye et al., 2016), many environmental factors, such as temperature, humidity, airflow velocity and indoor chemistry, etc., can affect the emission rates and alter the occupant exposure to VOCs (Liang et al., 2014; Weschler, 2011). After all, the initial emittable concentration of VOCs within the materials would be the most important factor, since this initial concentration basically determines its total emissions during life time. However, it would be difficult for consumers to select low VOCcontaining materials beforehand without proper information. Regulated source control and labeling scheme on materials therefore are crucial in terms of affecting human behavior on material selection and ultimately improving indoor air quality. 3.9. Cooling and heating methods in Chinese dwellings Energy consumption is another constraint condition that can pose impacts on the selection of ventilation modes. Although detailed energy usage and future development is beyond the scope of this review, a few key points need to be briefly addressed as they may be strongly related to human behavior, indoor air pollution and ventilation mode development. It has been mentioned in previous sections that mechanical ventilation system is rarely used among Chinese dwellings. On the contrary, cooling and heating is a much basic need for occupants. The overall patterns for cooling and heating are different. Although high-rise or super high-rise residential buildings are very common in cities, centralized cooling is still much less popular compared to split-type air conditioners, which is the dominating method for cooling in dwellings in summer throughout the country, especially in urban areas. In terms of heating in winter, district heating is now the prevailing method for Northern cities (there is a geographical line proposed N50 years ago that can be used to decide if the region is typically developing district heating or not (THUBERC, 2015)) and it also gets more attention and practices in Southern cities as well. At present, there is a huge debate on whether the Southern cities should be developing district heating on a large scale, however, the majority of residents still depend on the air conditioners, air-source heat pumps or other heating devices that directly use electricity (THUBERC, 2013). In rural areas, biomass combustion is still a major heating source in residents (THUBERC, 2016).

3.10. Limited data on indoor ventilation rates As noted by (Persily, 2016), ventilation rates are critical for interpreting indoor concentration measurements. It is important to include ventilation measurements and to describe the measurement methods in sufficient detail for interpreting the results. Usually, the room needs to be airtight (closed windows and doors) for 12 h prior to measuring the VOCs, according to the IAQ standard that is currently in effect in China, GB/T 18883-2002 (AQSIQ et al., 2002). It is not clear how good (or how poor) the ventilation rates are in Chinese dwellings. Unfortunately, very few studies measure ventilation rates or otherwise carefully characterize the ventilation design for residential buildings in China. Without sufficient data on residential ventilation rates, the relationship between the indoor pollutant concentration and health may be difficult to determine. However, this lack of information may not be critical to this review for the following three reasons. First, because most residential buildings still depend on natural ventilation, the performance of mechanical ventilation in residential buildings may not currently be a major issue. Second, as discussed in the previous section, the performance of natural ventilation depends on building location, group layout, orientation, internal space arrangement and openings. In principle, natural ventilation would be difficult to determine among different cities with various climate conditions; furthermore, human behavior also affects natural ventilation. Third, as discussed in previous sections, it is reasonable to assume that the effects of air pollutants on human health are universal. However, this paper focuses on Chinese-oriented problems, i.e., major indoor pollutants and their corresponding concentrations in Chinese residences, and the applicability of the two proposed ventilation solutions to Chinese residences. 4. Potential ventilation determinants 4.1. Indoor air quality standards and end-point basis The target list for indoor air pollutants was analyzed before analyzing control strategies and ventilation requirements. The recommendations of indoor pollutant concentration limits and the corresponding potential sensory and health effects on human are shown in Table 15. There are many available toxicological or epidemiological data to support exposure-health effects. However, the end-point basis summarized in Table 15 are mainly from World Health Organization (WHO), Agency for Toxic Substances and Disease Registry (ATSDR) and Office of Environmental Health Hazard Assessment, California (CA OEHHA). The indoor pollutant concentration recommendations provided by the non-compulsive Chinese indoor air quality standard GB/T 18883-2002 (AQSIQ et al., 2002) are also included in Table 15 (concentration limits for PM1.0, PM2.5, ethylbenzene, styrene, airborne fungi, are not defined by GB/T 18883-2002). Some of the concentration limits were given in units of ppmv and were converted to μg m−3. Since gasphase SVOC concentrations are usually low and the primary exposure pathways are oral and dermal, the concentration limits of SVOCs are not included in Table 15. Other pollutants that are related to cooking, e.g., benzo(a)pyrene, are also excluded. According to Table 15, most of the concentration limits for pollutants can be determined based on acute or chronic effects on human. The sensory effects of CO2 and formaldehyde are also used to set a concentration limit for comfort purposes. It is beyond the scope of this review to address all of the potential outcomes of exposure to air pollutants. However, it can be seen that there are still variations and gaps between the recommended concentrations for a single compound. In addition, most of the recommendations given by GB/T 18883-2002 are not consistent with the health-based concentration requirements to a large extend, except for CO, toluene and xylene. The measurement ranges for most of the pollutants obtained in Section 3 are also included for comparison. Although the data


715

Table 15 Summary on recommendations of indoor pollutant concentration limits and the corresponding potential sensory and health effects on human. The measurement range in this review for most of the pollutants was also included. Chemical

CO2 SO2

NO2

CO

O3

NH3

Formaldehyde

Benzene

Toluene

Ethylbenzene

Xylene

Measurement range

Indoor concentration limits Value

Exposure averaging time

10–360 μg·m−3 (Table 11)

1000 ppmv 500 μg·m−3 660 μg∙m−3 29 μg·m−3 240 μg·m−3 470 μg·m−3

24-hour 1-hour (acute) 1-hour (acute) 1- to14-day (acute) 1-hour (acute) 1-hour (acute)

500–71,700 μg·m (Table 11)

200 μg·m−3 40 μg·m−3 10,000 μg·m−3 23,000 μg·m−3

1-hour (acute) 1-year (chronic) 1-hour (acute) 1-hour (acute)

40–250 μg·m−3 (Table 11)

100,000 μg·m−3 35,000 μg·m−3 10,000 μg·m−3 7000 μg·m−3 160 μg·m−3 180 μg·m−3

15-minute (acute) 1-hour (acute) 8-hour 24-hour 1-hour (acute) 1-hour (acute)

30–2530 μg·m−3 (Table 11)

200 μg·m−3 3200 μg·m−3

1-h (acute) 1-h (acute)

1290 μg·m−3 200 μg·m−3 76 μg·m−3 100 μg·m−3 100 μg·m−3 55 μg·m−3 54 μg·m−3 40 μg·m−3 9 μg·m−3 10 μg·m−3 110 μg·m−3 27 μg·m−3

1- to14-day (acute) 1-year (chronic) 1-year or longer (chronic) 1-hour (acute) 30-minute (acute) 1-hour (acute) 1- to14-day (acute) 15- to364-day 8-hour/1-year (chronic) 1-year or longer (chronic) 1-hour (acute) 1-hour (acute)

31 μg·m−3 21 μg·m−3 3 μg·m−3 10 μg·m−3 200 μg·m−3 37,000 μg·m−3

1- to14-day (acute) 15- to364-day 8-h/1-year (chronic) 1-year or longer (chronic) 1-hour (acute) 1-hour (acute)

2054 μg·m−3 300 μg·m−3 1027 μg·m−3 23,661 μg·m−3 9464 μg·m−3 2000 μg·m−3 284 μg·m−3 200 μg·m−3 22,000 μg·m−3

1- to14-day (acute) 1-year (chronic) 1-year or longer (chronic) 1- to14-day (acute) 15- to364-day 1-year (chronic) 1-year or longer (chronic) 1-hour (acute) 1-hour (acute)

20–3240 μg·m−3 (Table 11)

−3

0.2–33,340 μg·m−3 (Table 6)

1–89,520 μg·m−3 (Table 7)

1–134,110 μg·m (Table 7)

−3

0–164 μg·m−3 (Table 7)

0.2– 56,420 μg·m−3 (Table 7)

−3

Styrene

PM2.5

3– 203 μg·m−3 (Table 7)

9–667 μg·m−3 (Tables 4 and 5)

9464 μg·m 2839 μg·m−3 700 μg·m−3

1- to14-day (acute) 15- to364-day 1-year (chronic)

237 μg·m−3 21,000 μg·m−3

1-year or longer (chronic) 1-hour (acute)

23,214 μg·m−3 900 μg·m−3 4443 μg·m−3 75 μg·m−3 35 μg·m−3

1- to14-day (acute) 1-year (chronic) 1-year or longer (chronic) 24-hour 1-year (chronic)

10 μg·m

−3

1-year (chronic)

Sensory or health effects on human/end-point basis for the selected level

References

Sensory effects

GB/T 18883-2002 (AQSIQ et al., 2002) GB/T 18883-2002 (AQSIQ et al., 2002) CA OEHHA (OEHHA, 2016) ATSDR (ATSDR, 2016) GB/T 18883-2002 (AQSIQ et al., 2002) CA OEHHA (OEHHA, 2016)

Health effects on respiratory system Health effects on respiratory system

WHO (WHO, 2010)

Health effects on cardiovascular system

GB/T 18883-2002 (AQSIQ et al., 2002) CA OEHHA (OEHHA, 2016) WHO (WHO, 2010)

Health effects on respiratory system; eyes Health effects on respiratory system; eyes Health effects on respiratory system

Sensory irritation Sensory irritation on eyes Health effects on respiratory system

Health effects on hematologic system Health effects on immune system Health effects on hematologic system Health effects on immune system Health effects on respiratory, nervous systems; eyes reproductive or development Health effects on nervous system Health effects on nervous system Health effects on nervous system

Health effects on renal system Health effects on nervous and respiratory systems; eyes Health effects on nervous system Health effects on nervous and respiratory systems; eyes Health effects on nervous system Health effects on respiratory system; eyes; reproductive/development Health effects on nervous system

Associated with ~15% higher long-term mortality than 10 μg·m−3 The lowest level at which total, cardiopulmonary and lung cancer mortality have been shown to increase with N95% confidence in response to PM2.5

GB/T 18883-2002 (AQSIQ et al., 2002) CA OEHHA (OEHHA, 2016) GB/T 18883-2002 (AQSIQ et al., 2002) CA OEHHA (OEHHA, 2016) ATSDR (ATSDR, 2016) CA OEHHA (OEHHA, 2016) ATSDR (ATSDR, 2016) GB/T 18883-2002 (AQSIQ et al., 2002) WHO (WHO, 2010) CA OEHHA (OEHHA, 2016) ATSDR (ATSDR, 2016) CA OEHHA (OEHHA, 2016) ATSDR (ATSDR, 2016) GB/T 18883-2002 (AQSIQ et al., 2002) CA OEHHA (OEHHA, 2016) ATSDR (ATSDR, 2016) CA OEHHA (OEHHA, 2016) ATSDR (ATSDR, 2016) GB/T 18883-2002 (AQSIQ et al., 2002) CA OEHHA (OEHHA, 2016)

ATSDR (ATSDR, 2016) CA OEHHA (OEHHA, 2016) ATSDR (ATSDR, 2016) ATSDR (ATSDR, 2016) CA OEHHA (OEHHA, 2016) ATSDR (ATSDR, 2016) GB/T 18883-2002 (AQSIQ et al., 2002) CA OEHHA (OEHHA, 2016) ATSDR (ATSDR, 2016) CA OEHHA (OEHHA, 2016) ATSDR (ATSDR, 2016) CA OEHHA (OEHHA, 2016)

ATSDR (ATSDR, 2016) CA OEHHA (OEHHA, 2016) ATSDR (ATSDR, 2016) JGJ/T 309-2013 (MOHURD, 2013) WHO (WHO, 2006)


716


Table 15 (continued) Chemical

PM10

Bacterial

Measurement range

46–1080 μg·m−3 (Tables 4 and 5)

6–3498 cfu·m−3 (Table 10)a

Relative humidity Radon (222Rn)

1.9– 524.6 Bq·m−3 (Table 13)b

Indoor concentration limits Value

Exposure averaging time

150 μg·m−3 70 μg·m−3

24-hour 1-year (chronic)

20 μg·m−3 2500 cfu·m−3

1-year (chronic)

40%–80% 30%–60% 400 Bq·m−3

During cooling in summer During heating in winter 1-year (chronic)c

Sensory or health effects on human/end-point basis for the selected level Associated with ~15% higher long-term mortality than 20 μg·m−3

References

GB/T 18883-2002 (AQSIQ et al., 2002) WHO (WHO, 2006)

GB/T 18883-2002 (AQSIQ et al., 2002) GB/T 18883-2002 (AQSIQ et al., 2002)

Associated with an excess lifetime risk of 1 per 100 and 1 per 1000 are 67 Bq·m−3 and 6.7 Bq·m−3 for current smokers and 1670 Bq·m−3 and 167 Bq·m−3 for lifelong nonsmokers, respectively

GB/T 18883-2002 (AQSIQ et al., 2002) WHO (WHO, 2010)

Note: The blanks in the column of end-point basis do not mean that the pollutant has no sensory- or health effects on human; a The concentration of airborne culturable fungi, instead of bacterial, was used to represent microbe in indoor air; b The minimum and maximum concentrations were measured under different ventilation conditions; c The so-called action level, i.e., action needs to be taken when the radon concentration is above this level.

summarized are not exhaustive and maybe only be revealing part of the problem, it is still obvious that the maximum reported concentrations of the indoor air pollutants are all greater than the recommended levels, except for only ethylbenzene and styrene. Hence, the indoor pollutant concentrations need to be lowered down to the corresponding acute, 8-hour or chronic concentration limits. Generally speaking, people usually stay home for a long time on a daily basis, in this sense, 8-hour or chronic (usually annual) concentration limits would be more suitable to match the time scale. The current GB/T 18883-2002 mainly focused on short-term effects and therefore, the regulated concentration limits are mostly for 1-hour exposure. Therefore, GB/T 18883-2002 may not be a good reference to ensure indoor air quality from long-term health end-points. In terms of CO2 (a surrogate for bioeffluents), the concentration recommended by (Pettenkofer, 1858) at 1000 ppmv is still in use in China. The concentration of CO2 has been debated for a very long time. A recent study shows that exposures to bioeffluents with CO2 at 3000 ppm can cause deleterious effects on occupants (Zhang et al., 2016a). However, the concentration of bioeffluents CO2 may not be easy to accumulate to a very high level in residential buildings unless with very low air change rates. Finally, there are many other criteria to quantify indoor air quality. For example, many building certificates worldwide provide indoor air quality requirements to building owners, designers and shareholders to follow and get credits. The requirements can also be very strict. However, some of the organizations who provide the certificate service are not entirely non-profit, the requirements from the building certificates are not included in Table 15 to avoid any conflict of interest. 4.2. Ventilation determinants selection Ventilation determinants are selected for further discussion on potential control strategies and comparison of the two ventilation modes for Chinese dwellings. GB/T 18883-2002 (AQSIQ et al., 2002) is chosen as the starting point for the target list; this standard limits the concentrations of indoor bacterial colony, radon, and 13 more chemical substances in indoor environments, including six inorganic substances (i.e., SO2, NO2, CO, CO2, NH3, and O3) and seven organic substances (i.e., formaldehyde, benzene, toluene, xylene, benzo(a)pyrene, PM10, and TVOC), respectively. After analyzing the applicability of each substance for the purpose of this review based on previous sections, CO2 (bioeffluents), VOCs (e.g., formaldehyde),

PM2.5 and SVOCs (phthalates), moisture/mold and radon are selected as target pollutants for this review (it is possible that other pollutants can also become ventilation determinants based on different criteria). The process and criteria are summarized as follows: 1) Many pollutants, such as SO2, NO2, CO, CO2, benzo(a)pyrene, and particulate matter, may be generated during burning processes (e.g., cooking and environmental tobacco smoking) (He et al., 2004; Jin et al., 2005; Junninen et al., 2009; Liu et al., 2013d; Zota et al., 2005). First, smoking was ignored in this review because emissions from smoking are not usually considered to be a continuous source and because it is not practical to account for a non-continuous emission source related to personal behavior. One possible way to address smoking is to encourage people to smoke in rooms that have an exhaust fan, e.g., a restroom. Second, it should be noted that SO2, NO2, CO and benzo(a)pyrene are also typical coal-burning products (Jin et al., 2005; Junninen et al., 2009; Liu et al., 2013d; Zota et al., 2005). Coal was a major source for individual heating during winter in northern China many years ago. Currently, more than half of the heating areas use district heating instead of individual heating (THUBERC, 2015), coal-burning originated pollutants can be expected to be reduced. Although coal burning is still a primary method for cooking and heating in less developed areas of rural China (Liu et al., 2011b), it is not pragmatic to implement mechanical ventilation rate using the two discussed methods (natural ventilation with an air cleaner and mechanical ventilation with an air filtration unit) in those areas. Third, cooking in the kitchen should be decoupled from other indoor emission sources when determining the minimum ventilation rate because the kitchen exhaust fan is directly responsible for removing cooking-generated pollutants. According to Table 11 (Section 3.6), the indoor air pollution of SO2, NO2, CO can be common in Chinese dwellings. However, besides background pollution in atmosphere (see Table 12 in Section 3.6), the majority of indoor sources should be dealt with by an exhaust fan in the kitchen. Moreover, although the efficiency of the exhaust fan is not sufficiently high in many cases and the usage of the fan may not meet its demand, the short-term emissions with local exhaust should be excluded from the control strategy of ventilation in non-kitchen areas (living room, bedroom and study, etc.). Therefore, SO2, NO2, CO, benzo(a)pyrene are not selected as target pollutants partially for their non-continuous emission characteristic in residential settings.


2) Due to industrial, agricultural or traffic emissions, many pollutants, such as SO2, NO2, CO, NH3, CO2, O3, formaldehyde, benzene, toluene, xylene, benzo(a)pyrene, and particulates, may originate outdoors typically via anthropogenic processes and are then brought indoors (Huang et al., 2012; Lu et al., 2015). Because the ventilation rate should be able to be implemented by the two proposed modes, if one pollutant cannot be efficiently filtered or treated by the air cleaner or the air filtration unit or if the concentration of the pollutant outdoors can easily exceed the concentration indoors, that pollutant should be excluded from the list. Thus, SO2, NO2, CO, NH3, O3 and benzo(a)pyrene are not selected partially because these pollutants can be brought indoors from the outside and because the concentrations may not be easily decreased by air cleaning or filtration technologies (Siegel, 2016; Zhang et al., 2011a). 3) In addition to burning (including cooking), many pollutants also have other indoor sources. Bioeffluents can be exhaled or emitted by humans (Fenske and Paulson, 1999), and NH3, formaldehyde, benzene, toluene and xylene (see Tables 6 and 7 in Section 3.3) can be emitted from building materials and consumer products (Lindgren, 2010; Liu et al., 2013e). Pollutants that have major indoor sources are included in the list, except for NH3. The emission characteristics of ammonia have been studied less than VOC emissions (Liu et al., 2013e); therefore, the ventilation outcome would be difficult to predict under various conditions. Although the typical indoor concentration of ammonia can be summarized by reviewing the literature (see Table 11 in Section 3.6), the value of the data was compromised without knowing the measurement mechanism because the data can come from very different measurement backgrounds. 4) Phthalates and other SVOCs can also be emitted and accumulate indoors (Wang et al., 2010a). Outdoor particles have become a national concern in recent years, and the coupling effect of particles and SVOCs has attracted increasing attention (Liu et al., 2015). SVOCs are not included in GB/T 18883-2002 (AQSIQ et al., 2002), however, according to Table 9 (in Section 3.4), the current status of indoor SVOC concentrations in residential buildings should be of significant concern. In addition, although ventilation is usually ineffective to remove indoor SVOCs, the ventilation strategies can have impacts on indoor particle concentration, distribution and settlement. Therefore, SVOC is selected as an additional ventilation determinant. 5) The concentrations of particles with three typical aerodynamic diameters, i.e., PM1.0, PM2.5 and PM10, were reviewed as target pollutants because most of the reported data in the literature focus on particles of these sizes. Only PM10 is regulated by GB/T 18883-2002 (AQSIQ et al., 2002), which also indicates that PM2.5 was not of national concern 15 years ago. Based on the information from Tables 4 and 5 (in Section 3.2), both indoor and outdoor particle pollution seems to be a common issue for Chinese dwellings. However, if we exclude cooking and kitchen from the discussion, particles are also originated mainly from outdoor. Therefore, particles should be a ventilation prerequisite because particles from outdoor air should be filtered before entering the room. It is well known that there are differences in thermophoresis, gravitational effect, and Brownian motion are exhibited between PM1.0, PM2.5 and PM10 (Rim et al., 2011; Zhou et al., 2016). Diverse effects of air cleaning devices on particle removal can also be expected. Since PM2.5 is of national primary concern, PM2.5 is considered as a ventilation prerequisite for discussion of control strategies. 6) TVOC were excluded from the target list mainly because the process of determining an adequate concentration limit and a corresponding ventilation requirement for TVOC would be much more complicated than the one for single organic compounds, such as formaldehyde and benzene. Furthermore, the definitions and quantitative analysis methods of VOCs and TVOC used in Europe, the USA and China are vary widely (Zhang et al., 2014b); therefore, it may not be rigorous to directly compare TVOC data, even when using only data reported in the Chinese literature.

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7) According to the discussion in Section 3.5, indoor moisture and mold can be a general problem among Chinese dwellings. Two major issues associated with indoor moisture/mold are, 1) little ventilation in dwellings in Northern cities in winter with district heating; and 2) high levels of humidity in dwellings in Southern cities. Since the ventilation methods can pose impacts on indoor humidity, mold is included in the discussion. Moreover, indoor RH can be used as a determinant for controlling purposes, regardless of the applicability. 8) Although the general picture shows that radon concentrations in indoor environment are prevailingly below 400 Bq m− 3, it is still included in the discussion mainly because ventilation can play an important role in altering the indoor concentration of radon. Ventilation modes are therefore discussed regarding their potential to reduce indoor radon concentration level. 5. Potential control strategies and requirements 5.1. Odor and CO2 As discussed in Section 3.1, because the occupant density in residential settings is usually low, the bioeffluent concentrations are not usually significant. Odor caused by healthy humans exhaling VOCs would probably be far below olfactory thresholds and would therefore be resulting in low ventilation requirements. Table 3 (in Section 3.1) is further derived to show the relationship between occupant density and the theoretical maximum air change rate to reach the olfactory threshold for five major VOCs that are exhaled by humans. The results are shown in Fig. 1(a). There are available methods (as prescriptions) to determine the ventilation rate for residential buildings in China, Europe and the USA, as summarized in Table 2; however, we used the mass balance method to investigate the ventilation requirement. One more issue which needs to be pointed out is that, airflow rate per person (m3 h− 1 ∙ person− 1 or L s− 1 ∙ person− 1) or airflow rate per square meter (m3 h− 1 m− 2 or L s−1 m−2) are two frequently used terms to characterize ventilation requirement. However, both airflow rate per person and airflow rate per square meter are indirectly linked to space volume, which is the bridge to link pollutant emissions, concentrations and ventilation rate requirements in terms of air flowrate. Thus, the term of average volume per person is used in this review to help directly assessing ventilation requirements. The derivation is shown below. In theory, the mass balance method can be used to link the air change rate and indoor compound concentration, as shown in Eq. (1), to determine whether a pollutant can be treated as a ventilation rate determinant. V

dy _ ¼ m−N∙V∙y dt

ð1Þ

where V is the volume of the room, m3, y is the concentration of the target _ is the emission rate of the target comcompound, μg m−3, t is time, s, m _ can be espound, μg s−1, and N is the air change rate, s−1. In this case, m _ ¼ p∙C∙Q , where p is the number of occupants, C is the timated using m compound concentration in the human exhaled air, μg m−3, and Q is the human respiratory rate, m3 s−1, which is assumed to be 7.5 L min−1 (1.25 × 10−4 m3 s−1). The steady state compound concentration can be estimated by setting the right side of Eq. (1) to zero; thus, Eq. (2) can be derived and rewritten as y¼

C∙Q NðV=pÞ

ð2Þ

where V/p is the average volume per person, m3 ∙person−1. Based on Table 2, the typical average area per person for Chinese residences is between 10 m2 ∙ person− 1 and 50 m2 ∙ person−1; assuming typical floor

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Fig. 1. The role of odor and CO2 concentrations in determining the ventilation requirements for residential buildings. (a) Theoretical maximum air change rate to reach olfactory thresholds VS average volume per person, based on the bioeffluent concentrations summarized in Table 3. (b) Theoretical air change rate VS quasi-steady state CO2 concentration at different average volumes per person.

height ranges of 2 m to 3 m, the average volume per person is assumed to be 20 m3 ∙person−1–150 m3 ∙person−1 for typical Chinese dwellings. According to GB 50736-2012 (MOHURD, 2012), N in Eq. (2) should be 0.45 h−1–0.70 h−1. According to Fig. 1(a), although both exhaled concentrations and olfactory thresholds are not fixed values, the designed ACHs are probably orders of magnitude higher than the maximum ACH to reach the olfactory threshold (approximately 10−6 h−1–10−1 h−1) for the five selected VOCs. Therefore, the indoor concentrations of ethanol and methanol would probably not be sensed by humans. Human odor may be an issue only if the residence is airtight and has little ventilation. Although indoor pollution and ventilation requirements for schools are beyond the scope of this review, the average volume per person range, which is estimated to be from approximately 2.7 m3 ∙person−1 to 14 m3 ∙ person−1 (MOHURD and AQSIQ, 2010), is also included in Fig. 1(a) to show the possibility of using odor to determine the ventilation rate for classrooms in schools. Owing to the high occupant density of these spaces, certain exhaled VOCs such as ethanol could possibly be sensed by humans at low ACH; thus, ventilation for classrooms should be able to at least dilute the odor to a level that cannot be detected. Conversely, VOCs emitted from building materials can cause odor or irritation effects in some residential buildings, as discussed in Section

3.3. However, the measurements summarized in Tables 6, 7 and 8 suggest that the odor and irritation caused by building materials are not considerable; most of the recorded concentrations were below the odor and irritation thresholds and can be expected to be even lower after a given time. Moreover, most of the measurements were taken after the windows were closed (for various hours), making it difficult to directly link the concentration to the odor threshold or ventilation requirements. Therefore, the odor issue caused by building materials was neglected in this review. The mass balance method is also used to determine the quasi-steady state CO2 concentration and the time needed to reach quasi-steady state. The CO2 concentration increments caused by exhalation are approximately 400 ppmv–1700 ppmv when the average volume per person is 20–150 m3 ∙ person−1 and the ACH is set to 0.45 h−1–0.70 h−1 (MOHURD, 2012), as shown in Fig. 1(b). The time for the indoor CO2 concentration to reach quasi-steady state is between approximately 6 h and 8 h. The CO2 concentrations in the atmosphere and in exhaled air are assumed to be 400 ppmv and 47,500 ppmv (mean values of 55,000 ppmv and 40,000 ppmv, (Zhang et al., 2016a)), respectively. Because the CO2 concentration can be an indicator for indoor bioeffluent pollution, the typical threshold for the indoor CO2 concentration is given as 1000 ppmv, as recommended by GB/T 18883-2002 (AQSIQ et al., 2002) (different CO2 concentration upper limits can be proposed; however, the method to examine the ventilation rate would be similar). According to Fig. 1(b), with the normal ventilation rates recommended by GB 50736-2012 (MOHURD, 2012), CO2 concentration can be N 2000ppmv for low average volume per person buildings, while the concentration can be lower than 800 ppmv for high average volume per person buildings, indicating that 0.7 h− 1 can be too low to maintain the CO2 concentration of the indoor environment at 1000 ppmv and that 0.45 h−1 may be more than enough. As a result, although odor should not be considered as a primary ventilation requirement determinant for residential buildings in China, CO2 can be. Theoretically, 0.3 h−1–2.0 h−1 is more appropriate for Chinese residences to dilute bioeffluent, if the 1000 ppmv threshold for CO2 is used. Taking a building with low average volume per person (20 m3 ∙ person−1) as an example, by increasing the ACH to 2.0 h−1, the time for the indoor CO2 concentration to reach quasi-steady state should be less than a few hours, making it a relatively effective way to dilute bioeffluents. On the other hand, although the time to reach quasi-steady state could be long for high average volume per person buildings, the indoor CO2 concentration would probably be lower than 1000 ppmv for an ACH of only 0.27 h−1–0.45 h−1. Although natural ventilation has the potential to accomplish the determined ventilation requirements based on the CO2 concentration, it can be difficult to ensure the indoor CO2 concentration below a certain level all the time in dwellings. For example, CO2 concentration can be elevated significantly in bedrooms when people choose to close the windows at night. On the contrary, mechanical ventilation has more advantages for maintaining a constant volumetric flow to limit indoor CO2 concentrations below a designated level or using more advanced demand-control technology based on fluctuations of ventilation determinants through technologies such as the variable air volume method (Hesaraki and Holmberg, 2015). Overall, it is more practical to control indoor CO2 concentration using mechanical ventilation. 5.2. PM2.5 5.2.1. Indoor/outdoor target concentrations As discussed in previous sections, kitchens are the main locations that generate particles, as cooking and other burning activities take place. Currently, the most efficient way to minimize human exposure to cooking-generated particles in the kitchen is to use an exhaust fan, despite the fact that whether an exhaust fan is sufficient for extracting most of the particles is still questionable (Gao et al., 2015). However, the kitchen exhaust fan is not usually considered as part of the effort


to meet the required ventilation rate to dilute indoor pollution for the whole house. Moreover, by excluding the particles and the exhaust fan in the kitchen, the particles in residential air are sourced from outdoors. This inference means that the particle (e.g., PM2.5 or PM10) concentration is not a ventilation rate determinant but instead a prerequisite for determining or implementing the ventilation rate. Fig. 2 further investigates the indoor and outdoor PM2.5 concentration relationships in residential buildings for both urban and rural China based on the measurement data summarized in Tables 4 and 5, respectively. Fig. 2 shows that clear and concerning patterns for the indoor/outdoor PM2.5 concentration in urban and rural dwellings. First, the outdoor PM2.5 mean concentrations are mostly greater than the indoor concentrations for urban dwellings, while the outdoor PM2.5 mean concentrations are usually lower than the indoor concentration in rural areas. Apparently, outdoor air pollution is a problem for many dwellings in urban areas due to industrial emissions and traffic pollution. Indoor sources (e.g., coal burning) dominate PM2.5 generation in rural areas where indoor ventilation or air purification methods are not available. Second, although the indoor PM2.5 concentration level is not regulated in China, 35 μg m− 3, as recommended by WHO (WHO, 2006) as a level of interim target 1, seems to be a reasonable entry level goal for Chinese indoor environments (see Table 15 in Section 4.1). Air filtration should be a necessity for Chinese dwellings and Chinese people. Third, all the measurements of outdoor PM2.5 concentrations were taken

Fig. 2. Indoor and outdoor PM2.5 concentration relationships for residential buildings for both urban and rural China, based on Tables 4 and 5, respectively. Each dot represents a pair of mean concentration data for indoor and outdoor PM2.5 from one study, and the error bars represent the corresponding minimum and maximum concentrations. (a) Urban residential buildings (based on Table 4). (b) Rural residential buildings (based on Table 5).

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before 2016, and most of the reported data exceed 75 μg m−3, especially in the urban areas. It should be noted that this 24-hour average concentration limit (class II) from GB 3095-2012 (MEP and AQSIQ, 2012) was published in 2012; however, it was only in January 2016 that this compulsory standard became effective. The outdoor air quality is expected to be better in the future. However, at present, residential indoor particle concentrations still need to be significantly decreased. 5.2.2. Selection criteria for air cleaners and filters As discussed in the Introduction section, natural ventilation (mainly window ventilation) with air cleaners and mechanical ventilation with air filtration are two recommended solutions for reducing indoor pollutant concentrations, especially particle concentrations, in Chinese residences. Between the two options, the former is more feasible with smaller energy and financial inputs compared to the latter. Currently, the underlying technology, mode of application, target contaminants, and effectiveness of air cleaning are very diverse. (Siegel, 2016; Zhang et al., 2011a) emphasized that both the primary impact (i.e., concentration reductions) and secondary impacts (e.g., energy use and by-product production) need to be considered; they concluded that the concentration reduction impacts of air cleaning/filtration need to be compared with the secondary consequences that arise from the use of air cleaners or filters (Bekö et al., 2007; Siegel, 2016). Regardless of the constraint of this unwanted consequence, a distinct difference between the two modes is that the particles need to be removed from the air by the air cleaners after coming indoors if using natural ventilation (or window ventilation), while the particles can be filtered prior to direct occupant exposure when using mechanical ventilation with air filtration. Therefore, in practice, the effectiveness of the air cleaner should be examined in advance to reduce human exposure to particles while simultaneously using this technology to capture particles. Fig. 3 illustrates the effects of an air cleaner on reducing the indoor PM2.5 concentrations under natural ventilation in typical Chinese residential settings; the ACH of 0.45 h−1–0.70 h−1 is not indicated because natural ventilation cannot intentionally control the minimum ventilation rate. The two sub-figures represent two extreme scenarios: the top is assumed to be a large space that is equipped with an air cleaner with a relatively low clean air delivery rate (CADR), while the bottom shows a small space that is equipped with an air cleaner with a relative high CADR. It can be concluded from Fig. 3 that the ratio of CADR to room volume (h− 1), which can be considered as an equivalent air change rate, has an impact on the applicability of air cleaners. In the low CADR-to-room volume ratio case (the top sub-figure in Fig. 3), it may take 1–2 h to decrease the indoor PM2.5 concentrations to below 35 μg m−3 when the outdoor concentrations are 100 μg m−3– 300 μg m−3 with a relatively low natural ventilation rate. It would be difficult to achieve the indoor concentration goal when the outdoor pollution is worse than 300 μg m−3 or the natural ventilation rate is high. In the high CADR-to-room volume ratio case (the bottom sub-figure in Fig. 3), it would be much easier to reduce the indoor PM2.5 concentrations even when the outdoor pollution is up to 500 μg m−3 or using a strong natural ventilation rate with moderate outdoor pollution. Although Fig. 3 is purely theoretical, clearly, the CADR-to-room volume ratio (an “equivalent air change rate”), instead of the CADR value, needs to be considered when selecting air cleaners or implementing ventilation requirements for residential buildings that use natural ventilation. This ratio can be often overlooked in practice. Although Fig. 3 provides a detailed look and a theoretical reference for selecting air cleaners, simulations are not exhaustive. A table that shows the relationship between applicable area of an air cleaner and outdoor particle concentrations can be more practical for this purpose, as provided by GB/T 188012015 (AQSIQ and SAC, 2015). The reason for proposing Fig. 3, despite many idealistic assumptions being made, is to use the CADR value in the process of selecting devices and materials with adequate efficacy in response to various outdoor

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Fig. 3. The applicability of using air cleaners to reduce indoor PM2.5 concentrations under natural ventilation with atmospheric particle pollution in typical Chinese residential settings, based on mass balance and the following assumptions: 1) constant natural ventilation rate; 2) particle cleaning efficiency of 100%; and 3) particle natural decay in the indoor environment is neglected.

pollution levels. To some extent, CADR can be used to evaluate the quality of the air cleaners. On the quantitative side, the cumulate clean mass (CCM) can also be used to assess the long-term required capacity for air filters (and air cleaners). In principle, the required capacity is related to two parameters, i.e., the outdoor particle design concentration and the indoor particle concentration threshold. Currently, the indoor particle concentration threshold is not officially included in the Chinese national IAQ standard GB/T 18883-2002 (AQSIQ et al., 2002), and there is still no consensus on the indoor particle concentration threshold. Partially because the threshold is mostly an outcome of exposure and health effects, which is beyond the scope of this review, we mainly focus on the outdoor design concentration. Similar to cooling and heating loads in summer and winter, respectively, the concept of outdoor design PM2.5 concentration can also be used to determine the necessary capacity (i.e., filtration load) for residences to purify air in various cities. Instead of using the typical annual mean concentration, the guarantee rate was proposed by (Wang et al., 2015b) to statistically calculate the outdoor PM2.5 design concentration based on the idea that sufficient clean air should be provided by filters (or air cleaners) to partially cover the whole year. The idea is to determine a PM2.5 concentration level that the daily concentration would be below for a certain time of the year (e.g., 80%, 95%, etc.). As shown in Table 16, the outdoor PM2.5 design concentrations (DC) at a 95% guarantee rate are compared for 31 cities in China using the corresponding annual mean concentrations (MC). The annual PM2.5 filtration load (FL) can be determined using Eq. (3), assuming that the indoor air does not need to be purified when the outdoor PM2.5 concentration is below the indoor concentration limit (Climit). 8 < 8760 ðC i −C limit ÞN t C i NC limit FL ¼ ∑ : i¼1 0 C i ≤C limit

ð3Þ

where Ci and Climit are the hourly outdoor PM2.5 concentration and the indoor PM2.5 concentration threshold, respectively, μg m− 3, and t is the time interval (t = 1), h. Eq. (3) can also be modified to use daily or monthly data if necessary. By setting Climit = 0, the annual maximum PM2.5 filtration load (MFC) can be derived using Eq. (4). Both FL and MFL are also included in Table 16; MFL is calculated based on MC provided by (NBS and MEP, 2015), while FL is analyzed by hourly or daily PM2.5 concentration

data for all 31 cities published by local authorities and collected by the authors. 8760

FL ¼ ∑ C i N ¼ 8760MC∙N i¼1

ð4Þ

It can be noted from Table 16 that MCs range from 34 μg m− 3 to 124 μg m−3, while DCs are two to three times these values, with the range of 70 μg m−3 to 325 μg m−3 for all 29 cities. The transition from MC to DC may have large impacts on designing or selecting proper air purification devices and materials due to the following aspects. First, with the help of Fig. 3, better air purification devices and materials can be selected to ensure sufficient capacity to clean the air while shortening the required time. Second, if 35 μg m−3 is considered to be the target indoor PM2.5 concentration, cities, such as Fuzhou, may not be required to clean the air based on the MC value (34 μg m−3); however, the DC value (70 μg m−3) shows that although the annual mean concentration is below 35 μg m−3, the daily concentration can be up to 70 μg m−3 for 5% of the year. Therefore, residents in Fuzhou need to clean the air when the outdoor air quality is poor. In fact, only 30% to 40% of the time would the outdoor air PM2.5 concentrations be below the MC value for the studied cities (Wang et al., 2015b). The comparison of the annul FL and MFL ranges in Table 16 also shows that, while the maximum filtration load ranges from 0.09 μg m−3 to 0.76 μg m−3 for the 31 cities, the filtration load ranges can be significantly lowered by setting an indoor concentration limit of 35 μg m−3. In addition, FL values can be b10% of the MFL values for Lhasa and Haikou because these two cities both have MC values of b35 μg m− 3. Although the MC value for Shijiazhuang is up to 124 μg m−3, the FL value can be still decreased by approximately 25%. It can be expected that by calculating the filtration load based on a presumed indoor concentration limit, the air filtration devices and materials will be more cost effective due to the decreased annually accumulated particle concentration that needs to be filtered. 5.3. Formaldehyde and other VOCs 5.3.1. Long-term emission patterns The need to consider formaldehyde or other VOCs in indoor ventilation requirements was demonstrated in Tables 6 and 7, which showed that indoor VOC pollution is serious in Chinese residential buildings across the country. Parallel to particle filtration, VOCs in outdoor air


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Table 16 Outdoor PM2.5 design concentrations at a 95% guarantee rate (Wang et al., 2015b), annual mean concentrations (NBS and MEP, 2015) and the annual filtration load and annual maximum filtration load estimated by assuming an indoor PM2.5 concentration limit of 35 μg·m−3 and that N ranges from 0.45 h−1–0.7 h−1. The results are based on ambient particle concentration data from 2014 for 31 cities (provincial capitals and municipalities in mainland China). City

DC, μg·m−3

MC, μg·m−3

FL, g·m−3

MFL, g·m−3

City

DC, μg·m−3

MC, μg·m−3

FL, g·m−3

MFL, g·m−3

Shijiazhuang Zhengzhou Jinan Beijing Tianjin Hefei Wuhan Xi'an Chengdu Shenyang Nanjing Changsha Harbin Taiyuan Changchun Chongqing

325 205 210 240 220 190 210 205 205 175 150 185 235 175 150 145

124 88 87 86 83 83 82 77 77 74 74 74 72 72 68 65

[0.36, 0.57] [0.21, 0.32] [0.22, 0.34] [0.22, 0.33] [0.21, 0.33] [0.19, 0.30] [0.20, 0.30] [0.17, 0.26] [0.16, 0.26] [0.16, 0.25] [0.16, 0.25] [0.16, 0.25] [0.18, 0.28] [0.15, 0.23] [0.14, 0.23] [0.12, 0.19]

[0.49, 0.76] [0.35, 0.54] [0.34, 0.53] [0.33, 0.53] [0.33, 0.51] [0.33, 0.51] [0.32, 0.50] [0.30, 0.47] [0.30, 0.47] [0.29, 0.45] [0.29, 0.45] [0.29, 0.45] [0.28, 0.44] [0.28, 0.44] [0.27, 0.42] [0.26, 0.40]

Hangzhou Xining Urumqi Lanzhou Yinchuan Shanghai Nanchang Guangzhou Nanning Guiyang Hohhot Kunming Fuzhou Lhasa Haikou

115 110 170 110 110 120 115 100 120 105 105 70 70 –a –a

65 63 61 61 53 52 52 49 49 48 46 35 34 25 23

[0.12, 0.18] [0.11, 0.17] [0.11, 0.18] [0.10, 0.16] [0.07, 0.11] [0.08, 0.13] [0.08, 0.13] [0.07, 0.11] [0.08, 0.12] [0.06, 0.10] [0.06, 0.10] [0.03, 0.04] [0.02, 0.03] [0.005, 0.01] [0.01, 0.02]

[0.26, 0.40] [0.25, 0.39] [0.24, 0.37] [0.24, 0.37] [0.21, 0.32] [0.20, 0.32] [0.20, 0.32] [0.19, 0.30] [0.19, 0.30] [0.19, 0.29] [0.18, 0.28] [0.14, 0.21] [0.09, 0.14] [0.10, 0.15] [0.13, 0.21]

a

DC values are provided for 29 cities by (Wang et al., 2015b), and Lhasa and Haikou are not included.

should also be purified by filters or air cleaners; however, indoor formaldehyde and other VOCs can be primarily considered as indoor pollutants. Currently, international ventilation standards have already included practical methods to determine the ventilation rate based on building floor area to account for material emissions (ASHRAE, 2016b; BSI, 2008). However, indoor VOC emissions are usually strongly related to the surface area of indoor decoration materials and furniture; moreover, concentrations are mainly determined by the room surface area-to-volume ratio, so determining a ventilation requirement based on floor area for residences may not be universally suitable. A notable pattern is that the emissions of formaldehyde and other VOCs from building materials usually follow a long-term decay curve, although fluctuations can be expected due to variations in the indoor environment. Fig. 4 further investigates the indoor formaldehyde concentration long-term decay pattern based on the measurement data summarized in Table 6. Although the data in Fig. 4 came from various sources, in general, the data suggest that formaldehyde emissions are probably unsteady within the first 3–6 months; after approximately 6–12 months, the emissions become quasi-steady state. Similar results could also be found for other VOCs, even though the data are not included in this review. In a sense, the VOC emissions from building materials can be roughly concluded to be a two-stage process, and the ventilation requirements can be determined accordingly as the two stages usually require different ventilation rates (Ye et al., 2014c). The ventilation requirements during the unsteady state period should be higher than those during the quasi-steady state period. Based on Table 15, there are both acute and chronic indoor formaldehyde concentration recommendations that aim to prevent occupants from various sensory or health effects. According to Fig. 4, under normal ventilation, the 100 μg m−3 level recommended by GB/T 18883-2012 may not be difficult to fulfil after 12 months. Considering that 100 μg m−3 is mainly a sensory-based guideline and may not be suitable for long-term exposure. However, the reality can be a little frustrating if we select stricter chronic concentration limit (9 μg m−3–10 μg m−3) by CA OEHHA (OEHHA, 2016) or ATSDR (ATSDR, 2016). Fig. 4 shows that the concentrations can be still much N 9 μg m−3–10 μg m−3 even after 2–3 years in Chinese dwellings. We should also keep in mind that there are many sources of indoor formaldehyde besides building materials, and therefore we still have a lot of work to do regarding source control. And when formaldehyde concentration is above the limit we select carefully, mechanical ventilation and other purification methods can be used.

5.3.2. Individual and composite-style VOC thresholds and the corresponding ventilation requirements One more issue associated with determining the ventilation requirement is the VOC concentration limits, which can be discussed in two parts. First, as mentioned in Sections 3.3 and 4.1, only a few VOCs are considered by the Chinese IAQ standard GB/T 18883-2002 (AQSIQ et al., 2002) or other international guidelines; both public awareness and engineering approaches for determining ventilation requirements mainly focus on formaldehyde. TVOC are also included in GB/T 18883 (AQSIQ et al., 2002) as mentioned in Section 4.2; however, because the definitions and measurements are usually diverse, unnecessary confusions arise when comparing the data. Furthermore, the concentrations of those VOCs that have critical adverse health effects, e.g., benzene, are hidden among the abundant organic compounds. Second, currently, individual thresholds for formaldehyde or other VOCs are still the main method for regulating indoor VOC concentrations; however, the combined effects of VOCs (Peng et al., 2015) are rarely covered. A possible and practical solution is the lowest concentration of interest (LCI) concept (ECA, 1997); LCIs are health-based values that are widely used to evaluate material emissions after 28 days from a single product in a laboratory chamber test and thus serve as part of the labeling

Fig. 4. Indoor formaldehyde concentration long-term decay pattern based on measurement data taken in typical rooms in Chinese residences (data from storerooms were excluded), as summarized in Table 6. Each point represents the mean concentration of formaldehyde from one study cited in Table 6.

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scheme to enforce source control (AgBB, 2015; ECA, 2013). LCI schemes consist of hundreds of substances that all contribute to the tested emission level, making LCI a composite-style method for promoting source control of VOCs. Currently, although LCIs are applied primarily in product safety assessments in the European Union (EU), the idea of composite-style thresholds can be useful for prioritizing VOCs (Ye et al., 2017) or determining ventilation rates (Ye et al., 2014c). Regarding the methods for conducting ventilation requirements, similar to diluting CO2 concentrations, mechanical ventilation can provide constant or variable flowrates, while natural ventilation is less reliable. However, some of the VOCs emitted indoors can be locally treated by air cleaners to lower the demand of diluting by clean air; mechanical ventilation can only filter the air before supplying it to the room, and the pollutant concentrations stemming from indoor sources can only be diluted. 5.4. SVOCs Because SVOCs, e.g., phthalates, adhere to surfaces, SVOCs are inherently not suitable for a direct ventilation determinant. However, because SVOCs coincide with particles, we can also reduce SVOC exposure via inhalation by reducing indoor particle concentrations. In addition to the measured phthalate concentrations in multiple media in homes summarized in Table 9, the relationship between indoor particles and bounded SVOCs are well described by (Liu et al., 2015); therefore, no further demonstration is included in this review. One downside of using natural ventilation with air cleaner needs to be highlighted: particles with a relatively large size, e.g., PM10, are more likely to settle on the ground before being filtered by the air cleaners, while mechanical ventilation with air filtration can efficiently remove PM10. Therefore, exposure to SVOCs would more likely to occur due to settled dust accumulation caused by the hysteretic nature of using air cleaners to reduce particles inside the room under natural ventilation. Furthermore, because indoor particles are not usually completely eliminated, indoor particle concentrations or the related ventilation requirements may also be determined based on SVOC exposure limits via all the pathways, which remains a difficult task for now. 5.5. Moisture/mold Indoor moisture is a long-lasting issue confronting Chinese residents, despite that the moisture generated by human and human activities should be manageable since the occupant density in Chinese dwellings is usually not high. And according to GB/T 18883-2002, indoor RH ranges should be within the range from 40% to 80% and from 30% to 60% for cooling in summer and heating in winter, respectively. It seems that the prescribed ranges are also not strict, however, it can be difficult to achieve. There are many regions where outdoor humidity is relatively high throughout the whole year, especially in Southern China, and therefore using outdoor air to reduce indoor humidity is not applicable. And while outdoor humidity is not a year-long problem for other regions, in winter, the need for heating makes indoor environment a relatively airtight space (people tend to close windows when heating is on), so that the moisture and mold issues can be easily found, especially in Northern China. To solve indoor moisture issue, people usually focus on building envelops as the first step. Even though the solution of improving the heat and mass transfer of building envelope to adapt to seasonal changes can help reducing the possibility of mold growth in indoor environment, it needs to be flexible and adjustable. And outdoor climate, indoor source, ventilation and human behavior also need to be taken into account. In terms of ventilation, it is clear that one of the solutions to reduce indoor moisture contents in Northern China in winter is to ventilate more frequently since outdoor air is usually dry. And pre-heating the outdoor air before supplying to indoor space using mechanical ventilation can avoid the cold air issue caused by opening the windows or

directly supplying outdoor air using mechanical system without preconditioning. The additional cost for heating is another problem, however, it can be partially overcome by using heat recovery technologies. When it comes to a humid outdoor air situation, dehumidification needs to be implemented no matter what ventilation system (i.e., natural (window) or mechanical ventilation) is used. It should be pointed out that turning on the split-type air-conditioner alone to dehumidify is not the best solution, since no outdoor air is purposely introduced to indoor environment to dilute the concentration of indoor air pollutants.

5.6. Radon Radon is inherently ubiquitous in dwellings. Although it seems that indoor radon concentration levels among Chinese dwellings are generally not serious according to Table 13 (see Section 3.7), ventilation is still a critical factor to reduce occupants' exposure to indoor radon. This judgement is based on the indoor radon concentration level recommended by GB/T 18883-2002 (400 Bq m−3), which is greater than the concentrations obtained by most of the measurements. However, direct evidence shows that exposure-response relationship is best described as being linear, without a threshold (WHO, 2010), indicating that, the lower the radon concentration, the better. Even though this deduction may be true for all the pollutants, it is especially important for radon exposure. And if we adopt 167 Bq m−3 or 16.7 Bq m−3 listed in WHO's guideline as a concentration limit, the picture of radon exposure in Table 13 is no longer optimistic. Therefore, ventilation is still critical for reducing radon concentration and in this sense, mechanical ventilation can be more reliable, compared to natural or window ventilation.

6. Comparison of the two implemented ventilation methods As part of an ongoing discussion, two potential modes that represent two major trends for improving IAQ for Chinese residential buildings are: 1) natural (or window) ventilation with an air cleaner; and 2) mechanical ventilation with an air filtration unit. For comparison, the applicability, advantages and disadvantages of the two modes, as well as major indoor pollutant sources, outdoor pollutant sources that affect the ventilation requirements, the current indoor/outdoor pollution status, influence factors, applicability of ventilation determinants and potential methods for determining the ventilation requirements for typical residential indoor air pollutants, i.e., bioeffluents, particulate matter, VOCs, SVOCs, moisture/mold and radon are summarized in Table 17. The information summarized in Table 17 is primarily based on the available data and literature gathered in this review, the comparisons and conclusions are preliminary. While the details can be found in Table 17, a few limitations of this comparison should be noted. First, it is still too early to determine which mode is better for given conditions. Both the outdoor and indoor environments as well as the initial costs and energy consumption should be carefully evaluated before selecting one of the two modes. Second, although health was not extensively reviewed by the authors, the dose and end-point effect for some indoor air pollutants, including some SVOCs, are still not clear. Therefore, ventilation requirements or other necessary approaches are unknown. Third, the energy aspect is also not extensively included in this review; however, the energy consumption and cost are also very critical for the residents and even for the long-term energy goal of the country (THUBERC, 2016). Overall, the selection of the ventilation rate implementation mode should be based on the health effect along with environmental and economic conditions. While the general direction can be guided by central or local governments and the industry for different areas, customized solutions should be validated, encouraged and made available to the public.


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Table 17 Preliminary comparison of the applicability, advantages and disadvantages of the two solutions for typical indoor air pollutants in Chinese residences: 1) natural ventilation with an air cleaner and 2) mechanical ventilation with an air filtration unit. Bioeffluents

Particulate matter, e.g., PM2.5 Formaldehyde and other VOCs and PM10

Major indoor sources

■ Human exhalation, skins, etc.

■ Cooking activity ■ Environmental tobacco smoking ■ Kerosene heating ■ Wood burning

■ Solid and liquid building materials ■ Secondary products of indoor chemistry

Outdoor sources that affects ventilation requirements

■ May be ignored

■ Outdoor particles that originated from traffic, industry or forest and agriculture burning, etc.

Current indoor/outdoor pollution status

■ Not serious for residential buildings

■ Indoor pollution is generally serious across China ■ Outdoor pollution is severe for parts of the country

Influence factor for human exposure

■ Space occupant density

■ Human behavior, e.g., window opening habit

Applicability to be a ventilation determinant

■ Odor is not applicable ■ CO2 can be a candidate to indicate bioeffluent pollution

■ Particles are not determinants, but ventilation prerequisites that need to be purified prior to dilute other pollutants

■ Outdoor VOCs that originated from traffic, industrial activities, etc. ■ Indoor formaldehyde, benzene and it homologues' pollution is generally serious across China ■ Many other VOC pollution levels indoors are unknown ■ Decay pattern in long term ■ Indoor chemistry, e.g., ozone ■ Formaldehyde and other VOCs should be applicable to be ventilation determinants

Potential method to determine ventilation requirement

■ Based on upper limit of CO2 concentration ■ Mass balance method can be used

■ Although not included in home ventilation, kitchen ventilation requirement and strategy can be based on particle concentrations

Mode 1: Natural ventilation (or window ventilation) ■ Advantages ■ The ventilation needed to dilute bioeffluents can be manageable via natural ventilation

+ an air cleaner Applicable to small room with a high CADR air cleaner, when atmospheric particle pollution is not very serious and natural ventilation is not abundant ■ Can be used to filter indoor generated or infiltrated particles

Disadvantages

■ Natural ventilation is not always dependable, especially in terms of climate and many other factors, and thus CO2 concentration can't be managed intentionally

■ Exposure to particles and filter the particles simultaneously ■ Not applicable to large room with a low CADR air cleaner, especially when atmospheric particle pollution is serious and natural ventilation is abundant ■ Particles with big size, e.g., PM10, could be settled as dust

SVOCs

Moisture/mold

Radon

■ Additives, e.g., plasticizers and flame retarders ■ Consumer products. e.g., pesticides ■ Indoor burning activities, e.g., smoking, cooking, etc. ■ Bounded with particles that may be reduced by particle filtration ■ Many SVOCs, e.g., phthalates, are ubiquitous and not easy to eliminate the sources simply by ventilation

■ Human and human activities ■ Leakage due to construction problems

■ Soil and building materials

■ Moisture in outdoor air

■ Radon concentration in outdoor air

■ Indoor moisture issue is common in North and South of China for different causes

■ Indoor radon concentrations are generally not serious among Chinese dwellings

■ Interactions with particles



■ SVOCs are not applicable to be a determinant, but exposure can be reduced with particles

■ Humidity can be used as a ventilation determinant, although it can be difficult to control ■ Based on the target RH range, however, when outdoor air is humid, dehumidification should be applied

■ Radon is applicable to be a determinant

■ Mass balance, floor-area based or two-stage ventilation methods can be used to dilute indoor emitted VOCs

■ SVOCs exposure via inhalation of particles can be used to determine indoor particle concentration threshold

■ Certain VOCs in both indoor and outdoor air can be treated

■ SVOCs carried by indoor generated or infiltrated particles can be reduced

■ Exposure to VOCs and clean the VOCs simultaneously ■ Secondary pollution could be produced locally ■ The discontinuous usage of air cleaners is not matched to the continuous emissions of VOCs from materials

■ SVOCs carried by outdoor particles can't be blocked in the first place ■ Total mass of SVOC in the dust-phase could be increased by accumulation of settled dust

■ Based on the upper limit of radon concentration

■ When outdoor air is humid, temporarily closing windows may be applicable ■ When indoor humidity is low, no ventilation requirement for RH is needed ■ Dehumidification can be necessary for certain regions that outdoor air is humid throughout the whole year

■ When indoor radon concentration is low, no ventilation requirement for reducing radon is needed

■ Air change rate may not be adequate to dilute radon concentration


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Table 17 (continued) Bioeffluents

Particulate matter, e.g., PM2.5 Formaldehyde and other VOCs and PM10

SVOCs

Moisture/mold

Radon

□ Air cleaners can be easily controlled by occupants for partial space with partial time, the total treated volumetric air can be reduced. □ Micro-positive pressure can't be achieved and therefore, infiltration via building envelope can't be easily reduced. □ The initial cost and overall energy consumption can be reduced. Mode 2: Mechanical ventilation + an air filtration unit ■ Dehumidification ■ Air change rate ■ SVOCs carried ■ Certain VOCs in Advantages ■ Constant or variable air■ PM2.5, PM10 can be filmay be adequate and heat recovby outdoor paroutdoor air can flow rate can be contered prior to supply to to dilute radon ery can be inteticles can be be treated prior trolled based on CO2 indoors concentration grated to reduce blocked prior to to supply to in■ Infiltration may be reconcentration indoor humidity supply to doors duced by providing while saving indoors ■ Constant or varmicro-positive pressure energy iable airflow to indoors rate can be controlled based on typical VOC emissions Disadvantages ■ The airflow based on CO2 ■ Can't be used to filter ■ Secondary pol■ Can't be used to ■ Dehumidification ■ When radon conconcentration may not be indoor generated or inlution could be reduce SVOCs can be necessary centration in supadequate to dilute VOCs filtrated particles produced and exposure via infor certain reply air is higher supplied to indoor generated gions that outthan that of in indoors or infiltrated door air is humid door air, indoor ■ Indoor emitted particles throughout the radon VOCs can only whole year concertation can be diluted be raised Additional □ Mechanical ventilation system should be running for whole space with whole time to supply purified outdoor to indoor environment comments □ Although the initial and operation cost is bigger, the energy consumption can be reduced by heat recovery technologies

Additional comments

7. Summary and recommendations By examining the IAQ measured in N7000 dwellings (nearly 1/3 were newly decorated and were tested for VOCs, while the rest were tested for particles, SVOCs, moisture/mold, inorganic gases and radon) in China within the last ten years, many pollutants including particulate matter (mainly PM2.5 and PM10), formaldehyde, benzene, other VOCs, phthalates and other SVOCs were found to be ubiquitous. With very little prevention, oral, inhalation and dermal exposure to those pollutants is almost inevitable. Although government and industry efforts have been proposed to remit atmospheric and indoor originated pollutants, affordable and effective ventilation methods to reduce human exposure indoors are still unclear. Ultimately, two urgent questions should be addressed: 1) how to effectively determine adequate ventilation rates for Chinese residential buildings and 2) how to determine proper methods for implementing the ventilation requirements to improve residential IAQ in China under the given conditions. First, the ventilation rate usually needs to be regulated to protect occupants from exposure to harmful pollutants in the indoor air. For a long time, the nation-wide mandatory regulation of residential ventilation rate was not established because natural ventilation by opening windows was the primary method for improving IAQ. Almost ten years ago, China launched a program intended to revise its national HVAC design standard for civil buildings. After nearly five years of studying and debating, the GB 50736 standard, which is currently in effect, was published (MOHURD, 2012). In this standard, minimum ventilation rates covering N 30 types of spaces with various functions, including residential buildings, were brought together for the first time, unlike in the previous HVAC design standard published in 2003. Although the progress and outcomes of the developed regulations on the minimum ventilation rate have profound impacts on people's daily lives, there are still some issues that need to be considered for future regulations: ■ The ventilation rate can be determined using the occupant density or floor area; however, the concentrations of ventilation determinants heavily depend on the spatial density, so building height also needs to be considered. Therefore, theoretically, the ventilation rate should be given on a 3-dimensional basis instead of 2-

dimensional. Figs. 1 and 2 are examples of examining ventilation demands based on average volume per person. ■ Currently, PM2.5 has taken over PM10 as the main focus of particulate matter. The outdoor air pollutions of PM2.5 are reported repeatedly by authorities and the media. Air cleaning technologies are mainly designed based on the efficiency of removing PM2.5. However, the effects of particles with smaller sizes, e.g., PM1.0 or other submicrometer combustion products, on occupant health could also be serious. The related air cleaning methods and ventilation requirements (e.g., in the kitchen) may need more work. ■ The overall long-term decay pattern of VOC emissions makes it impractical to set the ventilation rate to a constant value. Although, a two-stage emission process can generally be recommended, the ventilation requirements for each stage still need to be carefully determined. Alternatively, by developing low-cost sensors with good reliability, VOCs can also be monitored and function as a direct ventilation determinant. ■ Although using ventilation to eliminate total SVOCs would be ineffective due to the bonding effects between SVOCs and particles, methods for determining indoor particle concentrations should be extended to also consider SVOC exposure. Second, the two potential ventilation modes were compared based on their advantages and disadvantages (see Table 17). In general, mode 2 has more reliable merits to ensure acceptable IAQ for occupants; however, mode 1 is more easily generalized due to its low cost and low energy consumption, especially because long-term energy consumption is critical for China's economy and environment (THUBERC, 2016). Detailed discussions of the energy consumption are not included in this review; however, the following directions are important for improving the living standards of the 1.4 billion residents in China. ■ Effective methods for purifying the indoor air. Currently, most of the technologies that are used to clean or filter the air have unexpected drawbacks; more advanced methods that have fewer by-products need to be developed. ■ In reality, people always expose to multiple pollutants simultaneously. Robust methods to optimize ventilation rates based on the combined effects of CO2, formaldehyde (and other VOCs), and


■

■

■

■

other determinants are encouraged. First, the combined health effects of multiple pollutants should be further discovered from the health end-points. Obtaining better relationships between the concentrations of mixture of pollutants and respiratory symptoms, asthma, allergy and other acute or chronic effects would be helpful for engineering to determine ventilation requirements and design ventilation systems accordingly. Second, taking mechanical ventilation for instance, the control logic should be able to consider multiple pollutants. Efficient methods to decouple kitchen ventilation with whole space ventilation. Currently, the exhaust fan in the kitchen is mainly used to extract particles during cooking. However, the exhaust airflow rate is usually 600 m3 h−1–1200 m3 h−1, which equals an ACH of approximately 2 h−1–4 h−1 (3 h−1 is required by GB 50736-2012). The effects of this short-term, high-volume mechanical exhaust on the distribution of the indoor air pollution and the independent whole room ventilation should be further investigated. High performance heat recovery technology to improve the energy efficiency of the mechanical ventilation system. Although health should always be the priority, energy is still a crucial issue for China. Despite other technical problems, the main reason that mechanical ventilation has not been popularized among Chinese families is the financial cost. Accurate prediction methods to take natural ventilation potential into account for the purpose of diluting indoor air pollutants should be established based on climate conditions. In other words, the applicability of using natural ventilation and an air cleaner would be compromised or constrained in some parts of the country, e.g., natural (or window) ventilation may not be applicable during winter in the cold or severe cold regions. Cost efficient solutions to improve IAQ in rural residences. Indoor air pollution is also serious in rural areas (see Table 5). The adaptability of the two modes to be applied to or customized for rural residential buildings should be discussed. In some rural areas, the residential living standards are still poor; kitchens and living areas (or other areas) are sometimes housed within a single space. Better solutions for reducing direct exposure to cooking-generated particles should be a priority.

Finally, after nearly twenty years of rapid development in China, huge achievements including a vast number of public buildings and an unrivalled transportation system across the country have transformed the daily lives of the Chinese people. However, severe and unprecedented environmental consequences, e.g., the large area of haze events, have accompanied these achievements and have triggered public awareness and demands of improved living quality, especially in residential indoor environments. Ventilation can sometimes be overlooked as being too simple or too easy to be sufficient. However, carefully and properly designed ventilation systems can effectively and significantly improve the IAQ of residential buildings for billions of Chinese residents. It is still not an easy task to develop affordable, applicable and general solutions for Chinese families, although a few options have been proposed and discussed. After all, a detailed and applicable road map for the future development of strategies for controlling exposures in dwellings in China is in great need. Future efforts are needed to develop better residential ventilation solutions to improve IAQ in China. Acknowledgment First of all, the authors are grateful to the Australia-China Centre for Air Quality Science and Management (ACC-AQSM) for helpful discussions in preparing the manuscript. This project is partially funded by the National Natural Science Foundation of China through Grant Nos. 21507102 and 51578387 and the China Postdoctoral Science Foundation through Grant No. 2015M570386. The authors also express deep appreciation to Prof. Furong Wu at Northwest A&F University in China

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and Prof. Hexi Zhang at Xinxiang Medical University in China for providing additional data and information from their studies. Chengquan Zhang is also acknowledged for collecting data. Finally, the authors are grateful for the valuable comments from the anonymous reviewers. References Adams, R.I., Bhangar, S., Dannemiller, K.C., Eisen, J.A., Fierer, N., Gilbert, J.A., et al., 2016. Ten questions concerning the microbiomes of buildings. Build. Environ. 109, 224–234. AgBB, 2015. Health-related Evaluation Procedure for Volatile Organic Compounds Emissions (VVOC, VOC and SVOC) from Building Products. Ausschuss zur gesundheitlichen Bewertung von Bauprodukten, Germany. Andersen, C.E., Bergsoe, N.C., Majborn, B., Ulbak, K., 1997. Radon and natural ventilation in newer Danish single-family houses. Indoor Air 7, 278–286. AQSIQ, NHFPC, MEP, 2002. GB/T 18883-2002 Indoor Air Quality Standard, Beijing. AQSIQ, SAC, 2015. GB/T 18801-2015 Air Cleaner. Standards Press of China, Beijing. ASHRAE, 2013. ANSI/ASHRAE Standard 55-2013 Thermal Environmental Conditions for Human Occupancy. ASHRAE, Atlanta, GA, USA. ASHRAE, 2016a. ANSI/ASHRAE Standard 62.1-2016 Ventilation for acceptable indoor air quality. ASHRAE, Atlanta, GA, USA. ASHRAE, 2016b. ANSI/ASHRAE Standard 62.2-2016 Ventilation for acceptable indoor air quality in residential buildings. ASHRAE, Atlanta, GA, USA. ATSDR, 2016. Minimal Risk Levels (MRLs) for hazardous substances. Agency for Toxic Substances and Disease Registry, Atlanta, GA, UAS (March 2016). Bai, Z., Dong, Y., Wang, Z., Zhu, T., 2006. Emission of ammonia from indoor concrete wall and assessment of human exposure. Environ. Int. 32, 303–311. Bekö, G., Clausen, G., Weschler, C.J., 2007. Further studies of oxidation processes on filter surfaces: evidence for oxidation products and the influence of time in service. Atmos. Environ. 41, 5202–5212. Bornehag, C.G., Sundell, J., Bonini, S., Custovic, A., Malmberg, P., Skerfving, S., et al., 2004a. Dampness in buildings as a risk factor for health effects, EUROEXPO: a multidisciplinary review of the literature (1998–2000) on dampness and mite exposure in buildings and health effects. Indoor Air 14, 243–257. Bornehag, C.G., Sundell, J., Sigsgaard, T., 2004b. Dampness in buildings and health (DBH): report from an ongoing epidemiological investigation on the association between indoor environmental factors and health effects among children in Sweden. Indoor Air 14, 59–66. Brelih, N., Seppänen, O., 2011. Ventilation rates and IAQ in European standards and national regulations. The Proceedings of the 32nd AIVC Conference and 1st TightVent Conference, Brussels. BSI, 2007. BS EN 15251-2007 Indoor Environmental Input Parameters for Design and Assessment of Energy Performance of Buildings Addressing Indoor Air Quality, Thermal Environment, Lighting and Acoustics. British Standards Institution, London. BSI, 2008. BS EN 15242:2007 ventilation for buildings. Calculation Methods for the Determination of Air Flow Rates in Buildings Including Infiltration. BSI. Bu, Z., Zhang, Y., Mmereki, D., Yu, W., Li, B., 2016. Indoor phthalate concentration in residential apartments in Chongqing, China: implications for preschool children's exposure and risk assessment. Atmos. Environ. 127, 34–45. Cain, W.S., Schmidt, R., 2009. Can we trust odor databases? Example of t- and n-butyl acetate. Atmos. Environ. 43, 2591–2601. Cao, G., Awbi, H., Yao, R., Fan, Y., Sirén, K., Kosonen, R., et al., 2014. A review of the performance of different ventilation and airflow distribution systems in buildings. Build. Environ. 73, 171–186. Cao, G., Jarek, K., Awbi, H., Larsen, T.S., Heiselberg, P., Streblow, R., et al., 2012. Thermal comfort and ventilation criteria for low energy residential buildings in building codes. The Proceedings of the 10th International Conference on Healthy Buildings (Healthy Buildings 2012), Brisbane, Australia. Carrer, P., Wargocki, P., Fanetti, A., Bischof, W., De Oliveira, Fernandes E., Hartmann, T., et al., 2015. What does the scientific literature tell us about the ventilation– health relationship in public and residential buildings? Build. Environ. 94 (1), 273–286. Chen, C., Zhao, B., 2011. Review of relationship between indoor and outdoor particles: I/O ratio, infiltration factor and penetration factor. Atmos. Environ. 45, 275–288. Chen, J., Wang, X., Steemers, K., 2013. A statistical analysis of a residential energy consumption survey study in Hangzhou, China. Energ. Buildings 66, 193–202. Chen, R., Liu, B., Zhang, Q., 2016. Air pollutants in newly decorated rooms during 2009– 2013 in Wuxi City. J. Environ. Hyg. 6, 82–84 (in Chinese). Chen, S., Yang, W., Yoshino, H., Levine, M.D., Newhouse, K., Hinge, A., 2015. Definition of occupant behavior in residential buildings and its application to behavior analysis in case studies. Energ. Buildings 104, 1–13. Cheng, H., Hu, M., Zhang, L., Wan, L., 2009. PM2.5 concentrations in indoor and outdoor air and their relationship in the fall of Beijing. J. Environ. Health 26, 787–789 (in Chinese). CO2.Earth, 2016. NOAA Monthly Data. (https://www.co2.earth/monthly-co2, accessed on August 19th). de Lacy, Costello B., Amann, A., Al-Kateb, H., Flynn, C., Filipiak, W., Khalid, T., et al., 2014. A review of the volatiles from the healthy human body. J. Breath Res. 8, 014001. Deng, B., Zhang, B., Qiu, Y., 2016. Analytical solution of VOCs emission from wet materials with variable thickness. Build. Environ. 104, 145–151. Devos, M., Patte, F., Rouault, J., Laffort, P., van Gemert, L.J., 1990. Standardized Human Olfactory Thresholds. IRL Press, Oxford. Dimitroulopoulou, C., 2012. Ventilation in European dwellings: a review. Build. Environ. 47, 109–125.

726


Dong, J., Yan, Z., Cao, J., 2015. Levels and variations of indoor and outdoor particulate matter concentrations of a high-rise apartment in winter, Xi'an. Sci. Technol. Rev. 33, 42–45 (in Chinese). ECA, 1997. Report No. 18. Evaluation of VOC Emissions From Building Products – SOLID Flooring Materials. EUR 17334/EN, ISBN 92-828-0384-8. Office for Official Publications of the European Communities, Luxembourg. ECA, 2013. Report No. 29. Harmonisation Framework for Health Based Evaluation of Indoor Emissions From Construction Products in the European Union Using the EULCI Concept. EUR 26168/EN, ISBN 978-92-79-33194-7. Publications Office of the European Union, Luxembourg. Fan, D., Cao, S., Zhang, Y., Huang, N., Dong, T., Zhao, X., et al., 2014. Preliminary study on indoor PM2.5 pollution levels of residents in Lanzhou during heating period. J. Environ. Health 31, 232–234 (in Chinese). Fang, J., Yang, X., Li, H., Dong, X., Li, Y., Tang, Z., et al., 2014. Survey of formaldehyde and TVOC in indoor air in families with children in Beijing and Wuhan. J. Environ. Health 31, 585–586 (in Chinese). Fang, L., Clausen, G., Fanger, P.O., 1998. Impact of temperature and humidity on the perception of indoor air quality. Indoor Air 8, 80–90. Fang, Z., Oouyang, Z., Liu, P., Sun, L., Wang, X., 2013. Characteristics of airborne microbial pollution in indoor environments in Beijing. Acta Sci. Circumst. 33, 1166–1172 (in Chinese). Fanger, P.O., 1988. Introduction of the olf and the decipol units to quantify air pollution perceived by humans indoors and outdoors. Energ. Buildings 12, 1–6. Feng, T., Lu, X., 2016. Natural radioactivity, radon exhalation rate and radiation dose of fly ash used as building materials in Xiangyang, China. Indoor Built Environ. 25, 626–634. Fenske, J.D., Paulson, S.E., 1999. Human breath emissions of VOCs. J. Air Waste Manage. Assoc. 49, 594–598. Fisk, W.J., Lei-Gomez, Q., Mendell, M.J., 2007. Individual risk of current asthma from exposure to dampness and mold in homes. Indoor Air 17, 334. Gao, J., Fang, Y., Jiang, C., Xu, B., Song, T., Cao, C., 2014. Relationship between indoor and outdoor particulate matter concentrations in a residential building in winter of Shanghai. J. Civ. Architectural Environ. Eng. 36, 110–114 (in Chinese). Gao, J., Jian, Y., Cao, C., Chen, L., Zhang, X., 2015. Indoor emission, dispersion and exposure of total particle-bound polycyclic aromatic hydrocarbons during cooking. Atmos. Environ. 120, 191–199. Gao, J., Zhao, F., Tian, Y., 2009a. Investigation on radon levels in Tianjin (translated from Chinese by Ye, Wei). Chin. J. Radiol. Health 18, 456–457 (in Chinese). Gao, X., Yu, Q., Gu, Q., Chen, Y., Ding, K., Zhu, J., et al., 2009b. Indoor air pollution from solid biomass fuels combustion in rural agricultural area of Tibet, China. Indoor Air 19, 198–205. Gong, M., Weschler, C.J., Liu, L., Shen, H., Huang, L., Sundell, J., et al., 2015. Phthalate metabolites in urine samples from Beijing children and correlations with phthalate levels in their handwipes. Indoor Air 25, 572–581. Gong, M., Weschler, C.J., Zhang, Y., 2016. Impact of clothing on dermal exposure to phthalates: observations and insights from sampling both skin and clothing. Environ. Sci. Technol. 50, 4350–4357. Gong, M., Zhang, Y., Weschler, C.J., 2014a. Measurement of phthalates in skin wipes: estimating exposure from dermal absorption. Environ. Sci. Technol. 48, 7428–7435. Gong, W., Zhao, Y., Luan, S., 2014b. Characteristics of PM1.0 and CO in rural indoor air of five Chinese provinces. Chin. Sci. Bull. (Chin Ver) 59, 1553–1563 (in Chinese). Gou, S., Li, Z., Zhao, Q., Nik, V.M., Scartezzini, J.-L., 2015. Climate responsive strategies of traditional dwellings located in an ancient village in hot summer and cold winter region of China. Build. Environ. 86, 151–165. Gu, Q., Gao, X., Chen, Y., Yu, Q., Yan, Z., Chen, L., 2009. The mass concentration characters of indoor PM2.5 in rural areas in Jiangsu Province. J. Fudan Univ. (Natural Science) 48, 593–597 (in Chinese). Gu, Z., Li, H., Zhao, J., Jia, L., 2008. Investigation of indoor decoration pollution in Sanmenxi. Chin. J. Public Health Eng. 7, 289–291 (in Chinese). Guo, M., Pei, X., Mo, F., Liu, J., Shen, X., 2013. Formaldehyde concentration and its influencing factors in residential homes after decoration at Hangzhou, China. J. Environ. Sci. 25, 908–915. Guo, Y., Kannan, K., 2011. Comparative assessment of human exposure to phthalate esters from house dust in China and the United States. Environ. Sci. Technol. 45, 3788–3794. Guo, Y., Wu, Q., Kannan, K., 2011. Phthalate metabolites in urine from China, and implications for human exposures. Environ. Int. 37, 893–898. Han, J., Xu, L., Zhang, Q., Ding, K., Zhang, D., 2014. Survey on indoor formaldehyde pollution in Wolong District, Nanyang (translated from Chinese by Ye, Wei). J. Med. Theory Pract. 27, 3217–3219 (in Chinese). Han, W., 2011. Investigation on indoor air pollution and dwellers' adverse reaction in Anyang City. Prev. Med. Tribune 17, 411–413 (in Chinese). Hao, C., 2015. Characteristics of Culturable Airborne Microbes in Indoor Environments in Hangzhou [Master Dissertation]. Zhejiang Gongshang University, Hangzhou, China (in Chinese). He, A., Yang, S., Li, C., Zhou, Y., Liu, J., 2009. Investigation on formaldehyde pollution of indoor air and its control measures in Zhuzhou City. Pract. Prev. Med. 16, 140–141 (in Chinese). He, C., Morawska, L., Hitchins, J., Gilbert, D., 2004. Contribution from indoor sources to particle number and mass concentrations in residential houses. Atmos. Environ. 38, 3405–3415. Hesaraki, A., Holmberg, S., 2015. Demand-controlled ventilation in new residential buildings: consequences on indoor air quality and energy savings. Indoor Built Environ. 24, 162–173. Hu, D., Yang, W., Song, J., He, B., Pan, H., 2011. Preliminary investigation on indoor radon concentrations and gamma radiation levels in Zhejiang Province (translated from Chinese by Ye, Wei). Chin. J. Radiol. Health 20, 77–79 (in Chinese).

Hua, Y., Cheng, Z., Wang, S., Jiang, J., Chen, D., Cai, S., et al., 2015. Characteristics and source apportionment of PM2.5 during a fall heavy haze episode in the Yangtze River Delta of China. Atmos. Environ. 123 (Part B), 380–391. Huang, H., Haghighat, F., Blondeau, P., 2006. Volatile organic compound (VOC) adsorption on material: influence of gas phase concentration, relative humidity and VOC type. Indoor Air 16, 236–247. Huang, K., Feng, G., Li, H., Yu, S., 2014. Opening window issue of residential buildings in winter in north China: a case study in Shenyang. Energ. Buildings 84, 567–574. Huang, L., Mo, J., Sundell, J., Fan, Z., Zhang, Y., 2013. Health risk assessment of inhalation exposure to formaldehyde and benzene in newly remodeled buildings, Beijing. PLoS One 8. Huang, S., Xiong, J., Cai, C.R., Xu, W., Zhang, Y., 2016. Influence of humidity on the initial emittable concentration of formaldehyde and hexaldehyde in building materials: experimental observation and correlation. Sci. Report. 6, 9. Huang, S., Xiong, J., Zhang, Y., 2015. Impact of temperature on the ratio of initial emittable concentration to total concentration for formaldehyde in building materials: theoretical correlation and validation. Environ. Sci. Technol. 49, 1537–1544. Huang, Y., Lee, S.C., Ho, K.F., Ho, S.S.H., Cao, N., Cheng, Y., et al., 2012. Effect of ammonia on ozone-initiated formation of indoor secondary products with emissions from cleaning products. Atmos. Environ. 59, 224–231. IARC, 2015. Agents Classified by the IARC Monographs, Volumes 1–112. International Agency for Research on Cancer, Lyon, France (last updated: 7 April 2015). Iinuma, Y., Kahnt, A., Mutzel, A., Böge, O., Herrmann, H., 2013. Ozone-driven secondary organic aerosol production chain. Environ. Sci. Technol. 47, 3639–3647. Jaakkola, M.S., Nordman, H., Piipari, R., Uitti, J., Laitinen, J., Karjalainen, A., et al., 2002. Indoor dampness and molds and development of adult-onset asthma: a populationbased incident case-control study. Environ. Health Perspect. 110, 543–547. Jian, Y., Guo, Y., Liu, J., Bai, Z., Li, Q., 2011. Case study of window opening behavior using field measurement results. Build. Simul. 4, 107–116. Jin, Y., Zhou, Z., He, G., Wei, H., Liu, J., Liu, F., et al., 2005. Geographical, spatial, and temporal distributions of multiple indoor air pollutants in four Chinese provinces. Environ. Sci. Technol. 39, 9431–9439. Jokl, M.V., 2000. Evaluation of indoor air quality using the decibel concept based on carbon dioxide and TVOC. Build. Environ. 35, 677–697. Junninen, H., Mønster, J., Rey, M., Cancelinha, J., Douglas, K., Duane, M., et al., 2009. Quantifying the impact of residential heating on the urban air quality in a typical European coal combustion region. Environ. Sci. Technol. 43, 7964–7970. Lai, A.C.K., Ho, Y.W., 2008. Spatial concentration variation of cooking-emitted particles in a residential kitchen. Build. Environ. 43, 871–876. Lan, X.-w., A-h, Mei, Pan, W.-j., 2010. The report on the indoor radon concentration of Guangzhou. Guangzhou Architecture 38, 23–26 (in Chinese). Le Quere, C., Raupach, M.R., Canadell, J.G., Marland, G., et al., 2009. Trends in the sources and sinks of carbon dioxide. Nat. Geosci. 2, 831–836. Lelieveld, J., Evans, J.S., Fnais, M., Giannadaki, D., Pozzer, A., 2015. The contribution of outdoor air pollution sources to premature mortality on a global scale. Nature 525, 367–371. Li, C., Wang, C., Wang, Y., Wang, R., 2013a. Survey and analysis on the status of indoor air formaldehyde contamination among residential apartments. J. Gansu Lianhe Univ. (Natural Science) 27, 29–32 (in Chinese). Li, F., Zheng, S., Xiang, J., Jin, S., Hu, H., 2010. Survey on indoor air pollution for residential builings after decoration in Yuhang District, Hangzhou (translated by Ye, Wei). China Prev. Med. 11, 952–953 (in Chinese). Li, J., Fu, X., Sun, Y., Lin, S., 2012. Investigation of indoor formaldehyde pollution in recent residential decoration in Zhaoqing City in 2008–2010. China Trop. Med. 12, 1400–1402 (in Chinese). Li, L., Chen, W., He, C., 2013b. Monitoring of benzene, toluene and xylene pollution of indoor air in the newly decorated tenements at different time. Occup. Health 29, 231–233 (in Chinese). Li, M., Zhang, L., 2014. Haze in China: current and future challenges. Environ. Pollut. 189, 85–86. Li, N., 2011. Impacts of Human Behavior on Energy Consumption of Residential Buildings in China's Hot Summer and Cold Winter Zone. [Doctoral Dissertation]. Chongqing University, Chongqing (in Chinese). Li, T., Cao, S., Fan, D., Zhang, Y., Wang, B., Zhao, X., et al., 2016. Household concentrations and personal exposure of PM2.5 among urban residents using different cooking fuels. Sci. Total Environ. 548–549, 6–12. Li, X., Zheng, B., Wang, Y., Wang, X., 2006. A survey of radon level in underground buildings in China. Environ. Int. 32, 600–605. Liang, W., Yang, C., Yang, X., 2014. Long-term concentrations of volatile organic compounds in a new apartment in Beijing, China. Build. Environ. 82, 693–701. Liang, X., Huang, Y., Mai, L., Huang, Z., Ke, X., 2009. Survey and research for indoor air quality after decoration in Yangjiang. Chin. J. Health Lab. Technol. 19, 1140–1142 (in Chinese). Lin, X., Shen, T., Yu, X., Wang, X., 2009. Characteristics of phthalate esters pollution in indoor settled dust. J. Environ. Health 26, 1109–1111 (in Chinese). Lindgren, T., 2010. A case of indoor air pollution of ammonia emitted from concrete in a newly built office in Beijing. Build. Environ. 45, 596–600. Little, J.C., Hodgson, A.T., Gadgil, A.J., 1994. Modeling emissions of volatile organic compounds from new carpets. Atmos. Environ. 28, 227–234. Little, J.C., Weschler, C.J., Nazaroff, W.W., Liu, Z., Cohen Hubal, E.A., 2012. Rapid methods to estimate potential exposure to semivolatile organic compounds in the indoor environment. Environ. Sci. Technol. 46, 11171–11178. Liu, A., Han, S., Yao, Q., Zhang, M., Cai, Z., 2013a. Characteristics of chemical composition of PM2.5 and its effect on visibility in autumn and winter of 2011 in Tianjin. J. Meteorology Environ. 29, 42–47 (in Chinese).

W. Ye et al. / Science of the Total Environment 586 (2017) 696–729 Liu, C., Cao, J., Zhang, Y., 2016. Simplifying analysis of sorption of SVOCs to particles: lumped parameter method and application condition. Int. J. Heat Mass Transf. 99, 402–408. Liu, C., Zhang, Y., Benning, J.L., Little, J.C., 2015. The effect of ventilation on indoor exposure to semivolatile organic compounds. Indoor Air 25, 285–296. Liu, Q.-y., Zhang, T.-t., Y-j, Liu, Wang, X.-x., 2011a. Investigation of Carbon Monoxide of Indoor Air From Residential Areas at Xicheng District, Beijng. 40. Journal of Shanghai Normal University (Natural Sciences), pp. 625–628 (in Chinese). Liu, Q., Liu, Y., Zhang, M., 2013c. Personal exposure and source characteristics of carbonyl compounds and BTEXs within homes in Beijing, China. Build. Environ. 61, 210–216. Liu, W., Zhang, Y., Yao, Y., 2013e. Labeling of volatile organic compounds emissions from Chinese furniture: consideration and practice. Chin. Sci. Bull. 58, 3499–3506. Liu, W., Zhang, Y., Yao, Y., Li, J., 2012. Indoor decorating and refurbishing materials and furniture volatile organic compounds emission labeling systems: a review. Chin. Sci. Bull. 57, 2533–2543. Liu, Y., Guo, Y., Liu, F., 2011b. Stoves improvement and indoor air pollution abatement in rural area in China. J. Environ. Health 28, 240–241 (in Chinese). Liu, Y., Luo, K., Li, L., Shahid, M.Z., 2013a. Fluoride and sulfur dioxide indoor pollution situation and control in coal-burning endemic area in Zhaotong, Yunnan, China. Atmos. Environ. 77, 725–737. Liu, Z., Li, A., Hu, Z., Sun, H., 2014. Study on the potential relationships between indoor culturable fungi, particle load and children respiratory health in Xi'an, China. Build. Environ. 80, 105–114. Liu, Z., Ye, W., Little, J.C., 2013b. Predicting emissions of volatile and semivolatile organic compounds from building materials: a review. Build. Environ. 64, 7–25. Logue, J.M., McKone, T.E., Sherman, M.H., Singer, B.C., 2011. Hazard assessment of chemical air contaminants measured in residences. Indoor Air 21, 92–109. Lu, C., Deng, Q.-H., Yu, C.W.F., 2015. Strategies for reduction of episodic risk of PM10 by controlling industrial and traffic emissions of SO2 and NO2 and meteorological parameters. Indoor Built Environ. 24, 473–488. Lu, R., Chen, Q., Huang, L., 2013. Investigation on indoor air pollution in decorated rooms and its prevention measures in Nanning City. Occup. Health 29, 1929–1930 (in Chinese). Lu, Z., Tu, Y., Yu, R., Xu, Z., 2010. Indoor radon levels and influencing factors in houses of Suzhou. Proceedings of the Third National Conference on Natural Radiation and Control, Baotou, China, pp. 217–221 (in Chinese). Luo, M., Zhou, X., Zhu, Y., Sundell, J., 2016. Revisiting an overlooked parameter in thermal comfort studies, the metabolic rate. Energ. Buildings 118, 152–159. Ma, H., Shao, X., Liang, C., Wang, H., Wu, C., Li, X., et al., 2016. Feasibility analysis on combination strategies of window ventilation and air cleaners in residential buildings under haze weather. J. HV AC 46, 18–23 (in Chinese). Ma, L., Dong, Z., Wu, K., Pan, J., 2015. Indoor air quality and characteristics of fine particles for rural Guizhou. Environ. Monit. in China 31, 28–34 (in Chinese). Marco, E., Grimalt, J.O., 2015. A rapid method for the chromatographic analysis of volatile organic compounds in exhaled breath of tobacco cigarette and electronic cigarette smokers. J. Chromatogr. A 1410, 51–59. Mei, A.-h., Liu, Z.-z., Pan, W.-j., 2016. Survey on radon concentration in recently built residences of Guangzhou. Guangzhou Architecture 44, 14–17 (in Chinese). MEP, 2013. Ministry of Environmental Protection of the People's Republic of China Briefs on the Air Quality of Selected Cities on January 30, the Total Areas Under Haze Condition Reached 1.43 Million Square Kilometers. (http://www.mep.gov.cn/gkml/hbb/ qt/201301/t20130130_245789.htm, accessed on Jun 5th, 2016, in Chinese). MEP, AQSIQ, 2012. GB 3095-2012 Ambient Air Quality Standards. China Environmental Science Press, Beijing. Missia, D.A., Demetriou, E., Michael, N., Tolis, E.I., Bartzis, J.G., 2010. Indoor exposure from building materials: a field study. Atmos. Environ. 44, 4388–4395. MOHURD, 2012. GB 50736-2012 Code for Design of Heating Ventilation and Air Conditioning. China Architecture & Building Press, Beijing, China. MOHURD, 2013. JGJ/T 309-2013 The Standard of the Measurement and Evaluation for Efficiency of Building Ventilation. China Architecture & Building Press, Beijing. MOHURD, AQSIQ, 2003. GB 50019-2003 Code for Design of Heating Ventilation and Air Conditioning. China Planning Press, Beijing, China. MOHURD, AQSIQ, 2010. GB 50099-2011 Code for Design of School. China Architecture & Building Press, Beijing. Morawska, L., Zhang, J., 2002. Combustion sources of particles. 1. Health relevance and source signatures. Chemosphere 49, 1045–1058. Mu, L., Deng, F., Tian, L., Li, Y., Swanson, M., Ying, J., et al., 2014. Peak expiratory flow, breath rate and blood pressure in adults with changes in particulate matter air pollution during the Beijing Olympics: a panel study. Environ. Res. 133, 4–11. Nazaroff, W.W., Goldstein, A.H., 2015. Indoor chemistry: research opportunities and challenges. Indoor Air 25, 357–361. Nazaroff, W.W., Weschler, C.J., 2004. Cleaning products and air fresheners: exposure to primary and secondary air pollutants. Atmos. Environ. 38, 2841–2865. NBS, MEP, 2015. China Statistical Yearbook on Environment 2014. China Statistics Press, Beijing. Nishi, Y., 1981. Measurement of thermal balance in man. In: Cena, K., Clark, J.A. (Eds.), Bioengineering, Thermal Physiology and Comfort. Elsevier, New York, pp. 29–39. Noh, K.-C., Hwang, J., 2010. The effect of ventilation rate and filter performance on indoor particle concentration and fan power consumption in a residential housing unit. Indoor Built Environ. 19, 444–452. NSB, 2015. China Statistical Yearbook-2015. China Statistics Press, Beijing. OEHHA, 2016. All OEHHA Acute, 8-hour and Chronic Reference Exposure Levels (chRELs) as of June 2016. (http://oehha.ca.gov/air/general-info/oehha-acute-8-hour-andchronic-reference-exposure-level-rel-summary, last accessed: September 12th, 2016.).

727

Ostro, B., Hu, J., Goldberg, D., Reynolds, P., Hertz, A., Bernstein, L., et al., 2015. Associations of mortality with long-term exposures to fine and ultrafine particles, species and sources: results from the California teachers study cohort. Environ. Health Perspect. 123, 549–556. Pei, X.Q., Song, M., Guo, M., Mo, F.F., Shen, X.Y., 2013. Concentration and risk assessment of phthalates present in indoor air from newly decorated apartments. Atmos. Environ. 68, 17–23. Peng, C., Lee, J.-W., Sichani, H.T., Ng, J.C., 2015. Toxic effects of individual and combined effects of BTEX on Euglena gracilis. J. Hazard. Mater. 284, 10–18. Peng, C., Yan, D., Wu, R., Wang, C., Zhou, X., Jiang, Y., 2012. Quantitative description and simulation of human behavior in residential buildings. Build. Simul. 5, 85–94. Persily, A., 2015. Challenges in developing ventilation and indoor air quality standards: the story of ASHRAE standard 62. Build. Environ. 91, 61–69. Persily, A., Gorfain, J., Brunner, G., 2005. Ventilation design and performance in U.S. office buildings. ASHRAE J. 47, 30–35. Persily, A.K., 2016. Field measurement of ventilation rates. Indoor Air 26, 97–111. Pettenkofer, M., 1858. Besprechung Allgemeiner Auf Die Ventilation bezüglicher Fragen (in Germany). Cotta, Munich. Qi, M.W., Li, X.F., Weschler, L.B., Sundell, J., 2014. CO2 generation rate in Chinese people. Indoor Air 24, 559–566. Qin, J., Li, M., Zhang, Q., Cui, S., Liu, W., Fan, Z., 2011. Indoor formaldehyde pollution in recent residential decoration. J. Environ. Occup. Med. 28, 363–365 (in Chinese). Reinikainen, L.M., Jaakkola, J.J.K., 2003. Significance of humidity and temperature on skin and upper airway symptoms. Indoor Air 13, 344–352. Rim, D., Green, M., Wallace, L., Persily, A., Choi, J.-I., 2011. Evolution of ultrafine particle size distributions following indoor episodic releases: relative importance of coagulation, deposition and ventilation. Aerosol Sci. Technol. 46, 494–503. Ruth, J.H., 1986. Odor thresholds and irritation levels of several chemical substances: a review. Am. Ind. Hyg. Assoc. J. 47, A-142–A-151. Shao, L., Hu, Y., Wang, J., Hou, C., Yang, Y., Wu, M., 2013. Particle-induced oxidative damage of indoor PM10 from coal burning homes in the lung cancer area of Xuan Wei, China. Atmos. Environ. 77, 959–967. Sherman, M.H., Hodgson, A.T., 2004. Formaldehyde as a basis for residential ventilation rates. Indoor Air 14, 2–9. Shi, S., Zhao, B., 2016. Occupants' interactions with windows in 8 residential apartments in Beijing and Nanjing, China. Build. Simul. 9, 221–231. Siegel, J.A., 2016. Primary and secondary consequences of indoor air cleaners. Indoor Air 26, 88–96. Singer, B.C., Coleman, B.K., Destaillats, H., Hodgson, A.T., Lunden, M.M., Weschler, C.J., et al., 2006. Indoor secondary pollutants from cleaning product and air freshener use in the presence of ozone. Atmos. Environ. 40, 6696–6710. Stojić, A., Maletić, D., Stanišić Stojić, S., Mijić, Z., Šoštarić, A., 2015. Forecasting of VOC emissions from traffic and industry using classification and regression multivariate methods. Sci. Total Environ. 521–522, 19–26. Su, J., Han, Q., Liu, J., Guo, Y., Feng, H., Xu, M., 2010. Variations and influencing factors of indoor radon concentrations in Urumqi. Radiat. Prot. 30, 305–311 (in Chinese). Sun, R., Han, B., Bai, Z., Kong, S., Zhang, N., He, F., et al., 2014. Characteristics and sources of elements of PM2.5 for indoor and personal exposure of children during winter in Tianjin. Res. Environ. Sci. 27, 1227–1235 (in Chinese). Sun, Z.-k., Kang, H.-x., Shen, Z.-x., Li, S., Wu, J., Tang, J., et al., 2011. Survey of residential indoor air microorganisms in cities in South and North China. J. Environ. Health 28, 130–132 (in Chinese). Sundell, J., 2004. On the history of indoor air quality and health. Indoor Air 14, 51–58. Sundell, J., Levin, H., Nazaroff, W.W., Cain, W.S., Fisk, W.J., Grimsrud, D.T., et al., 2011. Ventilation rates and health: multidisciplinary review of the scientific literature. Indoor Air 21, 191–204. Tang, Y., Wang, Y., Chu, Y., Yin, H., 2012. Survey on indoor formaldehyde pollution in residential buildings in Chengdu. J. Environ. Health 29, 265–266 (in Chinese). THUBERC, 2013. Annual Report on China Building Energy Efficiency (in Chinese). China Architecture & Building Press, Beijing. THUBERC, 2015. Annual Report on China Building Energy Efficiency (in Chinese). China Architecture & Building Press, Beijing. THUBERC, 2016. Annual Report on China Building Energy Efficiency (in Chinese). China Architecture & Building Press, Beijing. Tian, Y., Sul, K., Qian, J., Mondal, S., Ferro, A.R., 2014. A comparative study of walking-induced dust resuspension using a consistent test mechanism. Indoor Air 24, 592–603. Tichenor, B.A., Guo, Z., Sparks, L.E., 1993. Fundamental mass transfer model for indoor air emissions from surface coatings. Indoor Air 3, 263–268. Tischer, C.G., Heinrich, J., 2013. Exposure assessment of residential mould, fungi and microbial components in relation to children's health: achievements and challenges. Int. J. Hyg. Environ. Health 216, 109–114. Toftum, J., Jørgensen, A.S., Fanger, P.O., 1998a. Upper limits for indoor air humidity to avoid uncomfortably humid skin. Energ. Buildings 28, 1–13. Toftum, J., Jørgensen, A.S., Fanger, P.O., 1998b. Upper limits of air humidity for preventing warm respiratory discomfort. Energ. Buildings 28, 15–23. Tomoto, T., Moriyoshi, A., Sakai, K., Shibata, E., Kamijima, M., 2009. Identification of the sources of organic compounds that decalcify cement concrete and generate alcohols and ammonia gases. Build. Environ. 44, 2000–2005. Tong, D., Huang, S., 2008. Investigation of formaldehyde pollution in newly decorated residential buildings in Wenzhou (translated from Chinese by Ye, Wei). Conn. Med. 14, 179–180 (in Chinese). Tse, L.A., IT-s, Yu, Qiu, H., JSK, Au, X-r, Wang, 2011. A case-referent study of lung cancer and incense smoke, smoking, and residential radon in Chinese men. Environ. Health Perspect. 119, 1641–1646. Tsushima, S., Bekö, G., Bossi, R., S-i, Tanabe, Wargocki, P., 2016. Measurements of dermal and oral emissions from humans. Proceedings of the 14th International Conference

728


on Indoor Air Quality and Climate – Indoor Air. 2016. Universiteit Gent, Ghent, Belgium. Uhde, E., Salthammer, T., 2007. Impact of reaction products from building materials and furnishings on indoor air quality—a review of recent advances in indoor chemistry. Atmos. Environ. 41, 3111–3128. Uhde, E., Schulz, N., 2015. Impact of room fragrance products on indoor air quality. Atmos. Environ. 106, 492–502. Wang, F., Meng, D., Li, X., Tan, J., 2016a. Indoor-outdoor relationships of PM2.5 in four residential dwellings in winter in the Yangtze River Delta, China. Environ. Pollut. 215, 280–289. Wang, L., Zhao, B., Liu, C., Lin, H., Yang, X., Zhang, Y., 2010a. Indoor SVOC pollution in China: a review. Chin. Sci. Bull. 55, 1469–1478. Wang, Q., Li, G., Meng, C., Zhao, L., Wang, J., Wang, X., 2015a. Penetration of outdoor fine particulate matter (PM2.5) through building envelope and passive control methods. J. HV&AC 45, 8–13 (in Chinese). Wang, Q., Li, G., Zhu, R., Wang, J., Zhao, L., Wang, X., et al., 2015b. Determination of PM2.5 outdoor design concentration for air filter design and selection. Build. Sci. 31, 71–77 (in Chinese). Wang, S., Ding, W., Li, C., 2010a. Investigation on indoor formaldehyde pollution in new urban district of Yongchuan, Chongqing. J. Environ. Occup. Med. 27 (441-442+446, in Chinese). Wang, S., Wei, W., Li, D., Aunan, K., Hao, J., 2010b. Air pollutants in rural homes in Guizhou, China – concentrations, speciation, and size distribution. Atmos. Environ. 44, 4575–4581. Wang, X., Chen, J., Sun, J., Li, W., Yang, L., Wen, L., et al., 2014a. Severe haze episodes and seriously polluted fog water in Ji'nan, China. Sci. Total Environ. 493, 133–137. Wang, X., Liu, W., Huang, C., Cai, J., Shen, L., Zou, Z., et al., 2016b. Associations of dwelling characteristics, home dampness, and lifestyle behaviors with indoor airborne culturable fungi: on-site inspection in 454 Shanghai residences. Build. Environ. 102, 159–166. Wang, X., Tao, W., Xu, Y., Feng, J., Wang, F., 2014b. Indoor phthalate concentration and exposure in residential and office buildings in Xi'an, China. Atmos. Environ. 87, 146–152. Wang, Y., Cui, L., Zhou, L., Wu, J., Zhang, X., Ding, Z., et al., 2013. Investigation of indoor PM2.5 and PM1.0 in some houses in Nanjing. J. Environ. Health 30, 900–902 (in Chinese). Wang, Z., Li, S., Wei, X., Ouyang, P., Yan, J., Wang, L., 2008. Effect of house indoor air pollution on children respiratory system in Lanzhou city. J. Environ. Health 25, 873–876 (in Chinese). Waring, M.S., 2014. Secondary organic aerosol in residences: predicting its fraction of fine particle mass and determinants of formation strength. Indoor Air 24, 376–389. Waring, M.S., Siegel, J.A., 2013. Indoor secondary organic aerosol formation initiated from reactions between ozone and surface-sorbed D-limonene. Environ. Sci. Technol. 47, 6341–6348. Wei, X.-y., Han, X., Cui, Y.-y., Zhang, Y.-w., Huang, C., 2016. Study on mould growth in dwelling building of Shanghai (in Chinese). Building Energ. Environ. 35, 27–30. Weschler, C.J., 2000. Ozone in indoor environments: concentration and chemistry. Indoor Air 10, 269–288. Weschler, C.J., 2009. Changes in indoor pollutants since the 1950s. Atmos. Environ. 43, 153–169. Weschler, C.J., 2011. Chemistry in indoor environments: 20 years of research. Indoor Air 21, 205–218. Weschler, C.J., 2016. Roles of the human occupant in indoor chemistry. Indoor Air 26, 6–24. Weschler, C.J., Wisthaler, A., Cowlin, S., Tamás, G., Strøm-Tejsen, P., Hodgson, A.T., et al., 2007. Ozone-initiated chemistry in an occupied simulated aircraft cabin. Environ. Sci. Technol. 41, 6177–6184. WHO, 2006. WHO Air Quality Guidelines for Particulate Matter, Ozone, Nitrogen Dioxide and Sulfur Dioxide: Global Update 2005: Summary of Risk Assessment. WHO Regional Office for Europe, Copenhagen, Denmark. WHO, 2010. WHO Guidelines for indoor air quality: selected pollutants. WHO Regional Office for Europe, Denmark. Wisthaler, A., Weschler, C.J., 2010. Reactions of ozone with human skin lipids: sources of carbonyls, dicarbonyls, and hydroxycarbonyls in indoor air. Proc. Natl. Acad. Sci. 107, 6568–6575. Won, D., Magee, R., Yang, W., Lusztyk, E., Nong, G., Shaw, C., 2005. A material emission database for 90 target VOCs. Proceedings of Indoor Air 2005. 2, Beijing, China, pp. 2070–2075. Wouter Borsboom, T., De Gids, N.W., Logue, J., Sherman, M., Wargocki, P., 2016. Technical Note AIVC 68 Residential Ventilation and Health. INIVE EEIG, Belgium. Wu, F., Wang, W., Man, Y.B., Chan, C.Y., Liu, W., Tao, S., et al., 2015. Levels of PM2.5/PM10 and associated metal(loid)s in rural households of Henan Province, China. Sci. Total Environ. 512–513, 194–200. Wu, H., Liu, Z., Gao, X., 2016a. Investigation and influence factors of formaldehyde pollution in indoor air. Occup. Health 32 (957-959+961, in Chinese). Wu, J.-g., Z-j, Zhuang, C-j, Niu, C-x, Tang, Lu, G.-l., Xu, H.-p., 2010. Association of indoor air pollutants exposure with respiratory symptoms in children. Chin. Journal of Dis. Control Prev. 14, 899–902 (in Chinese). Wu, X., Zhang, Q., Xiao, Y., Qiu, X., Zhang, B., Wu, Y., 2014. Jiangsu Province' indoor radon levels and public dose evaluation. Radiat. Prot. 34, 118–123 (in Chinese). Wu, Y., Cox, S.S., Xu, Y., Liang, Y., Won, D., Liu, X., et al., 2016b. A reference method for measuring emissions of SVOCs in small chambers. Build. Environ. 95, 126–132. Xiao, Y., Xiao, D., Tang, L., 2011. Investigation on natural radioactivity levels indoor in Hengyang and Xiangtan in Hunan Province. Radiat. Prot. 31, 317–322 (in Chinese). Xiong, J., Wang, L., Bai, Y., Zhang, Y., 2013a. Measuring the characteristic parameters of VOC emission from paints. Build. Environ. 66, 65–71.

Xiong, J., Wei, W., Huang, S., Zhang, Y., 2013b. Association between the emission rate and temperature for chemical pollutants in building materials: general correlation and understanding. Environ. Sci. Technol. 47, 8540–8547. Xiong, J., Zhang, Y., 2010. Impact of temperature on the initial emittable concentration of formaldehyde in building materials: experimental observation. Indoor Air 20, 523–529. Xu, G., Zhao, Y., Wu, H., Zhang, H., 2014. Investigation on concentration of formaldehyde in indoor air of new decorated housing in Xinxiang. Occupation and Health 30, 2326–2327 (in Chinese). Xu, J., Zhang, J.S., 2011. An experimental study of relative humidity effect on VOCs' effective diffusion coefficient and partition coefficient in a porous medium. Build. Environ. 46, 1785–1796. Xu, L.-p., Ge L-q, Gu Y., G-j, Zou, Wang, Z., Zhu, G.-z., 2013. Investigation of indoor radon concentration and gamma radiation levels in Chengdu area. China Environ. Sci. 33, 351–356 (in Chinese). Xu, R.-c., M-m, Gui, J-z, Peng, 2011. Investigation on indoor radon concentration levels in Xiamen, China. J. Environ. Health 28, 225–226 (in Chinese). Xu, Y., Hubal, E.A.C., Little, J.C., 2010. Predicting residential exposure to phthalate plasticizer emitted from vinyl flooring: sensitivity, uncertainty, and implications for biomonitoring. Environ. Health Perspect. 118, 253–258. Xue, S., 2012. The Distribution and Sources Apportionment of PM2.5, PM10 and Carbon Components in the Indoor and Outdoor of Qianhu Campus of Nanchang University [Master Dissertation]. Nanchang University, Nanchang (in Chinese). Xue, S., Ma, Y., Li, L., Huang, Y., Wang, J., 2011. Investigation of indoor formaldehyde pollution in newly decorative residences. J. Civ. Architectural. Environ. Eng. 33, 124–128 (in Chinese). Yaglou, C.P., Riley, E.C., Coggins, D.I., 1936. Ventilation requirements. ASHVE Trans. 42, 133–162. Yan, D., O'Brien, W., Hong, T., Feng, X., Burak Gunay, H., Tahmasebi, F., et al., 2015. Occupant behavior modeling for building performance simulation: current state and future challenges. Energ. Buildings 107, 264–278. Yang, Y., 2015. Investigation of indoor air quality in the residence in Xi'an. Contam. Control Air Con. Technol. 115–118 (in Chinese). Ye, W., Little, J.C., Won, D., Zhang, X., 2014a. Screening-level estimates of indoor exposure to volatile organic compounds emitted from building materials. Build. Environ. 75, 58–66. Ye, W., Won, D., Zhang, X., 2014b. Practical approaches to determine ventilation rate for offices while considering physical and chemical variables for building material emissions. Build. Environ. 82, 490–501. Ye, W., Won, D., Zhang, X., 2014c. A preliminary ventilation rate determination methods study for residential buildings and offices based on VOC emission database. Build. Environ. 79, 168–180. Ye, W., Won, D., Zhang, X., 2016. Examining the applicability of empirical models using short-term VOC emissions data from building materials to predict long-term emissions. Build. Simul. 9, 701–715. Ye, W., Won, D., Zhang, X., 2017. A practical method and its applications to prioritize volatile organic compounds emitted from building materials based on ventilation rate requirements and ozone-initiated reactions. Indoor Built Environ. 2, 166–184. Yu, C.W.F., Kim, J.T., 2012. Long-term impact of formaldehyde and VOC emissions from wood-based products on indoor environments; and issues with recycled products. Indoor Built Environ. 21, 137–149. Zhai, L., Xu, Z., Zhao, J., 2010. Disccusion on the relationship bewtween indoor formaldehyde concentration and move in time for residential buildings (translated from Chinese by Ye, Wei). Pract. Prev. Med. 17, 1584–1585 (in Chinese). Zhang, G., Dai, M., 2012. Research on the relationship of radon concentrations between soil and indoor environment. Energ. Technol. Manag. 134-135 (in Chinese). Zhang, H., Yoshino, H., 2010. Analysis of indoor humidity environment in Chinese residential buildings. Build. Environ. 45, 2132–2140. Zhang, L., Wang, F., Ji, Y., Jiao, J., Zou, D., Liu, L., et al., 2014a. Phthalate esters (PAEs) in indoor PM10/PM2.5 and human exposure to PAEs via inhalation of indoor air in Tianjin, China. Atmos. Environ. 85, 139–146. Zhang, Q.-C., Xia, B.-S., Yang, Z.-N., Chen, J.-G., 2014a. Studies on the problems concerning definition and quantitative characterization of volatile organic compounds at home and abroad. Pollut. Control Technol. 27, 3–7 (in Chinese). Zhang, Q., Lu, X.-M., Zhang, X.-L., Sun, Y.-G., Zhu, D.-M., Wang, B.-L., et al., 2013a. Levels of phthalate esters in settled house dust from urban dwellings with young children in Nanjing, China. Atmos. Environ. 69, 258–264. Zhang, R., Tao, J., Wei, J., Ma, Y., Li, T., Wang, C., et al., 2014b. Pollution levels and distribution characteristics of PM2.5 in indoor air. J. Environ. Health 31, 1082–1084 (in Chinese). Zhang, S., Li, Y., Liu, G., 2009. Investigation on formaldehyde pollution of indoor air of resident's house. J. Med. Forum 30 (67-68+71, in Chinese). Zhang, X., Wargocki, P., Lian, Z., Thyregod, C., 2016a. Effects of exposure to carbon dioxide and bioeffluents on perceived air quality, self-assessed acute health symptoms, and cognitive performance. Indoor Air http://dx.doi.org/10.1111/ina.12284. Zhang, X., Zillig, W., Künzel, H.M., Mitterer, C., Zhang, X., 2016b. Combined effects of sorption hysteresis and its temperature dependency on wood materials and building enclosures – part I: measurements for model validation. Build. Environ. 106, 143–154. Zhang, Y., Li, B., Huang, C., Yang, X., Qian, H., Deng, Q., et al., 2013b. Ten cities cross-sectional questionnaire survey of children asthma and other allergies in China. Chin. Sci. Bull. 58, 4182–4189. Zhang, Y., Mo, J., Li, Y., Sundell, J., Wargocki, P., Zhang, J.J., et al., 2011a. Can commonlyused fan-driven air cleaning technologies improve indoor air quality? A literature review. Atmos. Environ. 45, 4329–4343.

W. Ye et al. / Science of the Total Environment 586 (2017) 696–729 Zhang, Y., Xiong, J., Mo, J., Gong, M., Cao, J., 2016c. Understanding and controlling airborne organic compounds in the indoor environment: mass transfer analysis and applications. Indoor Air 26, 39–60. Zhang, Z., Liu, G., Peng, C., Yu, S., Yan, Y., Huang, G., et al., 2011b. Current status of indoor air pollutants in urban areas of Shenzhen. J. Environ. Hyg. 1, 10–13 (in Chinese). Zhao, J., 2009. Indoor Radon Concentrations and Radon Exhalation Rates of Building Materials in Shanghai [Master Dissertation]. Fudan University, Shanghai, China. Zhao, W., Bai, Z., Ma, L., 2008. Concentration of formaldehyde, benzene homologues and TVOC in indoor air in Shijiazhuang. Urban Environ. Urban Ecol. 21, 9–11 (in Chinese). Zheng, H., Qian, C., Ye, Y., Zhang, R., Shi, Y., Zhao, R., et al., 2011. Survey on indoor air quality in residential buildings in Beijing (translated from Chinese by Ye, Wei). J. Environ. Health 28, 1106–1107 (in Chinese). Zheng, K., Li, M., Shen, F., Qin, J., 2014. Analysis of air pollution in decorating residences in Baoshan District of Shanghai. Occupat. Health 30, 537–539 (in Chinese). Zhou, C., Wang, Z., Chen, Q., Jiang, Y., Pei, J., 2014. Design optimization and field demonstration of natural ventilation for high-rise residential buildings. Energ. Buildings 82, 457–465.

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Zhou, K., Zhao, Z., Zhang, J., Dong, X., Cheng, Y., 2010. Research on indoor radon concentrations and their influencing factors in Shijiazhuang regions. Radiation Protection 30 (312-315+322, in Chinese). Zhou, Y., Yang, C., Lam, Y.C., Huang, X., 2016. Thermophoresis of charged colloidal particles in aqueous media – effect of particle size. Int. J. Heat Mass Transf. 101, 1283–1291. Zhuo, W., Wang, X., Jin, Y., 2010. The Level of Indoor 222Rn Concentrations in 9 Cities of China. Proceedings of the Third National Conference on Natural Radiation and Control, Baotou, China, pp. 264–267 (in Chinese). Zota, A., Adarnkiewicz, G., Levy, J.I., Spengler, J.D., 2005. Ventilation in public housing: implications for indoor nitrogen dioxide concentrations. Indoor Air 15, 393–401. Zuraimi, M.S., Tham, K.W., 2008. Indoor air quality and its determinants in tropical child care centers. Atmos. Environ. 42, 2225–2239.