sustainability Article
Investigation of Indoor Air Quality and the Identification of Influential Factors at Primary Schools in the North of China Zhen Peng
, Wu Deng * and Rosangela Tenorio
Department of Architecture and Built Environment, the University of Nottingham Ningbo China, 199 Taikang East Road, Ningbo 315100, China;
[email protected] (Z.P.);
[email protected] (R.T.) * Correspondence:
[email protected] Received: 13 May 2017; Accepted: 1 July 2017; Published: 5 July 2017
Abstract: Over 70% of a pupil’s school life is spent inside a classroom, and indoor air quality has a significant impact on students’ attendance and learning potential. Therefore, the indoor air quality in primary school buildings is highly important. This empirical study investigates the indoor air quality in four naturally ventilated schools in China, with a focus on four parameters: PM2.5 , PM10 , CO2 , and temperature. The correlations between the indoor air quality and the ambient air pollution, building defects, and occupants’ activities have been identified and discussed. The results indicate that building defects and occupants’ activities have a significant impact on indoor air quality. Buildings with better air tightness have a relatively smaller ratio of indoor particulate matter (PM) concentrations to outdoor PM concentrations when unoccupied. During occupied periods, the indoor/outdoor (I/O) ratio could be larger than 1 due to internal students’ activities. The indoor air temperature in winter is mainly determined by occupants’ activities and the adiabatic ability of a building’s fabrics. CO2 can easily exceed 1000 ppm on average due to the closing of windows and doors to keep the inside air warmer in winter. It is concluded that improving air tightness might be a way of reducing outdoor air pollutants’ penetration in naturally ventilated school buildings. Mechanical ventilation with air purification could be also an option on severely polluted days. Keywords: indoor air quality; primary school; building air tightness; internal activities; air pollutants
1. Introduction China has been experiencing serious air pollution problems in recent years, due to rapid industrialization, urbanization, and increasing energy consumption [1–3]. The Chinese economy is still largely dependent on fossil fuels. In 2011, 69% of total energy consumption was contributed by coal combustion, 18% by oil, and 4% by natural gas. Only 8% of the national energy mix was from renewable sources such as hydroelectric, solar, and wind [4]. As a result, the ambient air has been heavily affected, especially in urban areas. Only 5 cities out of 367 in China met the World Health Organization (WHO)’s recommended air quality standards in 2012. The primary air pollutant in Chinese cities has been identified as suspended particulate matters (PMs), specifically, PM2.5 and PM10 . PM10 denotes inhalable particles with diameters that are generally 10 micrometers and smaller. PM2.5 denotes fine inhalable particles with diameters that are generally 2.5 micrometers and smaller [5]. The readings of PM2.5 concentrations in most urban areas have exceeded acceptable national standards, and are often worse in winter in the north of China due to fuel combustion for heating [6]. High exposure to particulate matters can bring morbidity problems like asthma, lung cancer, cardiovascular disease, respiratory diseases, birth defects, and premature death. Logue et al. [7] suggested that PM2.5 is one of the air pollutants which dominate health impacts in most U.S. residences Sustainability 2017, 9, 1180; doi:10.3390/su9071180
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due to chronic exposure. Such air pollutants lead to greater losses of disability-adjusted life-years (DALYs). Sundell et al. [8] concluded that the incidence of inflammation, respiratory infections, asthma symptoms, and short-term sickness is enhanced as a result of high exposure to air pollutants. Therefore, urban residents have to reduce the time they stay outdoors and their level of activity. However, it may not be safer to stay indoors, as some studies suggest that indoor air quality closely correlates to the outdoor pollution level, particularly in urban and industrial areas [9]. Another important factor which affects indoor air quality is building defects. Riley et al. [10] suggested that the penetration of particles through building cracks would significantly affect indoor air quality, especially for buildings where air exchange through openings or cracks is dominated by pressure differences arising from natural forces. Tian et al. [11] concluded that for naturally ventilated buildings, the key factors which determine occupants’ exposure to air pollutants were pressure difference, building air tightness, and air flow path. In addition, PM also can be generated by indoor activities, such as cooking, cleaning, cigarette smoking, and the movement of people. Abt et al. [12] found that cleaning activities and the movement of people significantly increased PM(0.7–10) concentrations by 0.27 µm3 /cm3 and 0.25 µm3 /cm3 , respectively, per minute in domestic buildings in Boston. Long et al. [13] investigated nine homes in Boston and figured out that dusting, vigorous walking, and sautéing were the key factors affecting indoor air quality. Apart from particulate matters, indoor air quality also can be affected by other parameters, such as carbon dioxide (CO2 ) level and indoor air temperature. Seppänen et al. [14] found that the risk of air-related health problems can be decreased when CO2 concentrations fall below 800 ppm. Fang et al. [15] indicated that indoor air temperature has great impact on perceived air quality in office buildings, and high air temperatures can promote the generation of other pollutants, such as volatile organic compounds (VOCs) and formaldehyde. Children are more sensitive when they are exposed to unhealthy air, because they generally breathe a higher volume of air relative to body weight at a faster rate [16,17]. Bakó-Biró et al. [18] figured out that over 30% of a pupil’s life was spent at schools, and about 70% of their time inside a classroom during school days. Shauhnessy et al. [19] claimed that poor indoor air quality caused by excessive CO2 and VOC concentrations have a negative impact on students’ attendance and learning potential, and lead to poor academic performance. Therefore, indoor air quality in school buildings is highly important, and may have a significant impact on a nation’s healthcare system. Haverinen-Shaughnessy et al. [20] investigated one hundred elementary schools in the southwest of the U.S. and found that 87% of the classrooms had air quality problems. Studies have also pointed out that indoor air pollutant concentrations in classrooms, such as CO2 , PM, and VOCs are greatly influenced by air pollution sources outside the school, primarily traffic and industrial emissions [21–24]. The PM concentration inside classrooms is partly determined by infiltration from the outside air. Zwo´zdziak et al. [25] concluded that there is a positive correlation between outdoor air pollution and indoor air quality, suggesting that urgent action should be taken to improve a building’s air tightness and reduce air infiltration. Amato et al. [26] investigated 39 primary schools in Barcelona and found that 53% of the indoor PM2.5 concentration measured could be traced back to seven outdoor sources in the ambient environment. Moreover, schools without paved playgrounds have an increased contribution by 5–6 µg/m3 on average compared to those with paved playgrounds. Janssen et al. [27] pointed out that schools close to roadways with heavy traffic usually have higher numbers of children suffering from bronchial hyper responsiveness, positive allergic sensitization, or both, compared with schools located far away from the traffic or industrial areas. In school buildings, the resuspension of particles by students’ indoor activities also affects the indoor particle concentration in occupied classrooms [28,29]. Lefcoe and Inculet [30] found that indoor activities, such as cleaning and children playing, had significant impacts on the indoor concentration of particles greater than 1 µm. Raunemaa et al. [31] reported that the average concentration of particles larger than 1.5 µm highly depends on the amount of time spent indoors. Another study from Majumdar et al. [32] indicated that PM2.5 and PM10 also can be produced when writing on the blackboard in a classroom.
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Apart from those chemical toxicants and particulate matters, it is found that the CO2 level may exceed 1500 ppm in classrooms in East London, which is much higher than the recommended level of 600 ppm from the Chartered Institution of Building Services Engineers (CIBSE) [33]. Ramalho et al. [34] investigated the indoor CO2 concentration in 489 mechanically ventilated classrooms in France, and the results indicated that 33% of the samples had a CO2 concentration above 1700 ppm, which is two times greater than the CIBSE value. In China, mechanical ventilation systems are not commonly used in public primary schools, and the only way to introduce fresh air into a classroom is to open windows and doors; however, particles and other air pollutants will be brought into the classroom simultaneously. Moreover, in winter, when the air pollution is the most serious in China, doors and windows are often closed to keep the inside warm. This may lead to two consequences: inadequate fresh air supply, and increased indoor air pollution from the combined effect of air penetration and indoor activity. Currently research related to indoor air quality in China has been focused on chemical toxicants, such as formaldehyde and benzene. Most studies were carried out in office buildings and residential houses. The indoor air quality in primary school buildings and the influential factors affecting indoor air quality (IAQ) have not been extensively investigated. Therefore, this empirical study aims to investigate indoor air quality in primary school buildings in China and identify the opportunities for improvement. 2. Research Methodology This research involves four case studies for primary schools in the North of China. These schools are all naturally ventilated, and were built in different times in compliance with different building construction codes. Field measurements were conducted in the selected classrooms in the four schools. The investigations and observations were also carried out with a focus on building defects and indoor activities. The purpose was to examine the links between outdoor air pollution, indoor air quality, building defects, and indoor activities. 2.1. Case Study Schools Four primary schools in Tai’an city were selected as case studies (Figure 1). Table 1 summarizes the characteristics of the selected school buildings. It should be noted that all of the classrooms selected have a similar floor area and floor height, and the same number of students, to facilitate comparisons. On the other hand, these buildings were built in different times, which leads to varying building compliances. For example, School D was completed in 2005, when the China Public Building Energy Saving Standard (GB50189-2005) [35] took effect, so external insulation, double glazed windows, and air tightness (level) were implemented. School B was completed in 2015 in accordance with the new version of the China Public Building Energy Saving Standard (GB50189-2015) therefore it has better insulation (lower U-values) and higher air tightness (level 6) compared to School D. Natural ventilation dominates air exchange in all measured school buildings. Thus, when doors and windows are closed, fresh air is brought in through gaps and cracks through the envelope. It is also noted that a heating system is not installed in these buildings, thus closing windows and doors helps to keep stable indoor temperatures in winter. This reduces air pollutant intake from outdoors; however the indoor air may become stale and unhealthy due to inadequate fresh air supply.
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Table 1. Characteristics of selected schools. Sustainability 2017, 9, 1180
A
B
C
D
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Size of classroom 70.56 m2 70 m2 65 m2 72 m2 Window type Double Triple Single Number of students 40 glazed 40 glazed 40 glazed Double 40 glazed 2K) 2K) Height of classrooms 3.6W/(m m 3.3W/(m m 3.4 m m 2K) Window U value 2.3 1.9 2.3 3.6 W/(m Constructed year Refurbished 2015 2003 ≥3.0) Air tightness 4 (2.5 ≥ in Q 2005 > 2.0) 6(1.5 ≥ Q > 1.0) ≤3(Q 4(2.52005 ≥ Q > 2.0) Wall-U value 0.6 W/(m2 K) 0.38 W/(m2 K) 0.6 W/(m2 K) Note: (1) value before 2005, no0.55 thermal public 2 K)for public buildings, therefore 2 K) Roof-U W/(m2requirements K) 0.28were W/(mset 0.55 W/(m buildings constructed before 2005 have no insulation, and the windows were single glazed. Also, the Window type Double glazed Triple glazed Single glazed Double glazed 2 K) 2 K) 2 K) Window U value 2.3 W/(m 1.9 W/(m 2.3 W/(m air tightness level was below 4. (2) Q is defined as the air volume flow rate per meter in length of Air tightness ≥ Qtightness > 2.0) ≥ Q >and 1.0) doors ≤ 3(Q ≥ 3.0) Q > 2.0) (3) Air for 6(1.5 windows were divided into4(2.5 five≥levels in cracks per hour (m3/m·h).4 (2.5 Note: before thermal regulation requirementsof were set for public buildings, public buildings constructed 2002 (1) based on2005, the no building GB/T7106-2002. In 2008,therefore the new building regulation of before 2005 have no insulation, and the windows were single glazed. Also, the air tightness level was below 4. (2) Q GB/T7106-2008 divided the air tightness into eight levels, where the higher the level the better the air 3 is defined as the air volume flow rate per meter in length of cracks per hour (m /m·h). (3) Air tightness for windows and doors were divided into five levels in 2002 based on theofbuilding regulation of GB/T7106-2002. 2008, the new tightness. (4) The earliest air tightness requirement windows and doors was from theInChina Public building of GB/T7106-2008 divided the air tightness into levels, where the the level Buildingregulation Energy Saving Standard GB50189-2005, and 4 was seteight as the minimum airhigher tightness levelthe in better the air tightness. (4) The earliest air tightness requirement of windows and doors was from the China Public 2005. Now the number has been replaced by 6 according to the latest China Public Building Energy Building Energy Saving Standard GB50189-2005, and 4 was set as the minimum air tightness level in 2005. Now the number been replaced by 6 according to the latest China Public Building Energy Saving Standard GB50189-2015. Saving has Standard GB50189-2015.
Figure 1. 1. Location Location of of selected selected primary primary schools schools in in Tai’an Tai’an City. Figure City.
2.2. Field Measurements Since the the central centralheating heatingsystem systeminin Tai’an annually heats buildings 15 November, Tai’an annually heats thethe buildings fromfrom 15 November, and and the heavy air pollution always happens after systemstarts startsworking, working,field fieldmeasurements measurements were the heavy air pollution always happens after thethe system carried out from 20 November 2016 to 10 December 2016. The measured parameters were particulate matter (PM2.5 and PM10), CO2, and indoor air temperature. The results were then compared to the recommended values from the China Indoor Air Quality Standard (GBT18883-2002), the World Health Organization (WHO), and the Chartered Institution of Building Services Engineers (CIBSE) (Table 2). In general, China has relatively lower requirements for PM2.5 and PM10. The annual mean value and 24 h mean value of PM2.5 in the Chinese Standards are 5 μg/m3 and 10 μg/m3 higher than
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matter (PM2.5 and PM10 ), CO2 , and indoor air temperature. The results were then compared to the recommended values from the China Indoor Air Quality Standard (GBT18883-2002), the World Health Organization (WHO), and the Chartered Institution of Building Services Engineers (CIBSE) (Table 2). In general, China has relatively lower requirements for PM2.5 and PM10 . The annual mean value and 24 h mean value of PM2.5 in the Chinese Standards are 5 µg/m3 and 10 µg/m3 higher than the WHO values. Also, the recommended annual mean value of PM10 is two times greater. Regarding CO2 concentration, China sets 1000 ppm as the upper limit, while WHO has divided CO2 concentration into three levels, and the acceptable level is 600 ppm. The measurements were conducted from 8:00 a.m. to 5:00 p.m. in a day. During the measuring hours, the windows were all closed due to low temperatures outside, and the measuring equipment was placed 1.5 m above the floor level at the center of the classrooms. A DUST TRAK model 8530 from TSI Inc., U.S. was used to measure the outdoor PM10 and PM2.5 , since it makes more noise during the measuring period. The indoor PM10 and PM2.5 concentrations were measured by a portable hand-held detector of BRAMC-SMART-126 model from China. The DUST TRAK model 8530 cannot measure PM2.5 and PM10 simultaneously; therefore, the PM2.5 was measured in the morning and the PM10 was measured in the afternoon. The temperature and the CO2 were measured by a recording detector of HTV-M model from PPM Company, U.K. Table 2. Guideline values for air quality pollutants from WHO, CIBSE, and China. Substance
Averaging Time
WHO Guideline Value
China Standard GB T18883-2002
PM2.5
Annual mean 24-h mean
10 µg/m3 25 µg/m3
15 µg/m3 35 µg/m3
PM10
Annual mean 24-h mean
20 µg/m3 50 µg/m3
40 µg/m3 50 µg/m3
CO2
Occupied period
