Day and night variability of atmospheric organic and elemental carbon ...

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Sustain. Environ. Res., 24(2), 107-116 (2014)

107

Day and night variability of atmospheric organic and elemental carbon during winter of 2011-12 in Agra, India Atar Singh Pipal,1 Rohi Jan,1 Deewan Singh Bisht,2 Atul Kumar Srivastava,2 Suresh Tiwari2 and Ajay Taneja1,* 1 Department of Chemistry Dr. B. R. Ambedkar University Agra 282002, India 2 Indian Institute of Tropical Meteorology New Delhi 110060, India

Key Words: PM2.5, carbonaceous aerosols, secondary organic aerosol, black carbon, India

ABSTRACT The mass concentrations of organic carbon and elemental carbon (OC and EC) associated with PM2.5 were investigated at a traffic influenced site (roadside) Kandhari, U.P. India during winter of 2011-12 by semi-continuous carbon analyzer. Individual samples of PM2.5 were collected for different time periods i.e., 24-h, day and night by medium volume air sampler and analyzed for OC and EC using thermal optical transmittance protocol. Average mass concentration of PM2.5 was 183 ± 114 µg m-3 and varied from 29 to 612 µg m-3. Carbonaceous analysis results showed that the average concentration of OC varied from 39 to 96 µg m-3 for 24-h, 71 to 89 µg m-3 for day and 64-91 µg m-3 for night while EC varied from 3.4-9.3, 8.9-16.8, 12.4-18.2 µg m-3 for 24-h, day and night samples respectively. The OC/EC was estimated which varied between 4.9-47, suggesting the presence of secondary organic aerosol. Carbonaceous aerosol account for 43% of the total PM2.5 mass in which the 38% OC and 5% EC contributed to total PM2.5 concentration. Day and night variation of carbonaceous aerosol was also studied and was found that the relative abundance of OC and EC was higher during day time. The high concentration of PM2.5 and its associated carbonaceous aerosol species at this site may be due to vehicular activities, biomass and fossil fuel combustion. Strong correlation between OC, EC and PM2.5 (r = 0.83-0.97) was observed for 24-h samples. Average level of secondary organic carbon was 46 µg m-3 for 24-h, 27 µg m-3 for day and 35 µg m-3 for night, accounting for 73, 34 and 46% for 24-h, day and night samples of total OC, respectively. This indicates that the source of OC is from primary emissions as well as secondary emissions in this region. . INTRODUCTION Carbonaceous aerosol is a matter of concern, due to its complex impacts on human health [1] and the environment [2]. As it is a major component of ambient aerosols, it is important to know its contributions to total aerosol mass for the identification of aerosol sources and subsequently formulating effective control measures. The fine particles have high probability of deposition deeper into the respiratory tract and are likely to trigger or exacerbate respiratory diseases. These particles also have burdens of toxins, and can result in health consequences other than respiratory health effects. Künzli et al. [3] estimated the traffic *Corresponding author Email: [email protected]

particulate pollutants in Austria, France and Switzerland were found to cause 40,000 premature deaths, 25,000 new cases of chronic bronchitis and many chronic bronchitis episodes and asthma attacks. Moreover, health impact of assessment indicates that in developing countries 1-3 yr of life may be lost due to . traffic particulate pollution [4]. Carbonaceous particles, usually classified as organic carbon (OC) and elemental carbon (EC) are most important constituents of the fine fraction of PM, especially in highly industrialized and urbanized areas [5]. OC represents a large variety of organic compounds that can be classified into aliphatic, aromatic compounds, acids, etc and is formed from various

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Pipal et al., Sustain. Environ. Res., 24(2), 107-116 (2014)

sources (e.g., combustion, industrial, and natural sources) and complex atmospheric processes (direct emission, homogenous gas-phase oxidation, gasaerosol partitioning, heterogeneous oxidation, etc.). It also consists of water-soluble organic carbon (WSOC) and water-insoluble carbon compounds. WSOC is not only a major contributor to cloud condensation nuclei, but also probably involves in the complex and unknown aqueous phase chemistry of wet aerosol, fog, and clouds. WSOC is approximately 20-35% of OC fraction and 90% of it consists of oxygenated organic aerosol [6] within urban air. EC is a mixture of graphite-like particles and light-absorbing organic matter. Moreover, the surface of EC particles contains numerous adsorption sites that are capable of enhancing catalytic processes. EC may involve in some important chemical reactions involving atmospheric sulfur dioxide (SO2), nitrogen oxides (NOx), ozone and other gaseous compounds due to its catalytic properties [7]. Atmospheric OC and EC concentrations in developing countries have increased in recent decades with rapid economic growth. It is contributing 20-50% of atmospheric aerosol in heavy polluted . atmosphere [8]. Carbonaceous particles are partly directly emitted into the atmosphere by combustion of fossil fuels and biomass burning, as well as by non-combustion processes (these particles can be biological particles, plant fragments, soil derived humic material, etc.). The direct emission of carbonaceous particles from the source is called primary aerosol whereas another part of secondary organic aerosol (SOA) is formed from precursor gases by chemical reactions in the atmosphere [9]. Ram and Sarin [10] have suggested that during the winter time (Dec-Feb) the entire Indo Gangetic Plain (IGP) in northern India provides an ideal site to study the role of primary pollutants and secondary aerosol formation due to fog haze weather conditions and reduction in visibility. Furthermore carbonaceous aerosol combustion accounts for 30-35% of the total suspended particulate (TSP) mass over IGP . during the winter time [10]. The present study has been conducted at roadside which is directly affected by heavy traffic on national highway (NH-2) - recognized as one of the major sources of particulate air pollution [11]. Therefore, to understand transport mainly from sources region i.e., IGP, and transformation characteristics of anthropogenic air pollutants and their effect on various aspects of regional and global environment changes, it is important to measure carbonaceous species. It may play an important role in global climate change by ejecting radiative forcing [12]. Thus, the OC and EC measurements become more important when considering personal exposure, local environmental effects, and effects on regional and global scales, such as radiative forcing effect. Therefore, the aim of the present study is (i) to characterize of PM2.5 in terms of carbonaceous aerosol species, (ii) to assess their probable sources

and their trends during day and night, and (iii) the formation of SOA during different time periods at a roadside monitoring station in Northern part of India. . MATERIALS AND METHODS 1. Site Description

.

Agra (27°10' N 78°02' E) is located in the North central part of the India, about 204 km of south of Delhi in the Indian state of Uttar Pradesh. It is one of the most famous tourist spots in India because of the presence of Taj Mahal, situated on the west bank of river the Yamuna. The climate during winter is cooled with moisture and the temperature ranges from 3.5 to 30.5 °C and downwind West-North-West i.e., WNW 9.4% and North-North-West 11.8%. The atmospheric pollution load was higher when wind blows from WNW because oil refinery at Mathura (50 km far from the centre of the city) is located there and pollutants may be transported. Agra has about 1.3 million inhabitants and the population density is about 21,150 persons km-2 with 386,635 vehicles registered and 32,030 generator sets. In Agra, 60% pollution is mainly due to vehicular emissions from three national highways (NH-2, NH-3 and NH-11) cross the city. Pipal et al. [11] have reported a high density of vehicular . traffic (105 vehicles d-1) on these three highways. 2. Sampling Site

.

PM2.5 samples were collected from a roadside i.e., Khandari site during winter season (2011-2012) (Fig. 1). The roadside is directly affected by heavy traffic emission on NH-2. This site is located about 200 m away from major national highway (NH-2) which is one of the busiest highways, connecting Delhi to Kolkata via Agra. Sharma et al. [13] have also found that approximately 6000-7000 vehicles passes daily this highway to several public institutions, schools, University, colleges, shoe factories, and transport Nagar. Apart from this, Inter State Bus Terminal is . situated approximately 2 km west of this site. 3. Sampling and Analysis

.

3.1. Sampling Aerosol samples of PM2.5 were collected on the roof of building at the roadside. The sampler was set up at the top (25 m above the ground) of the building roof. Aerosol samples were collected separately for 24-h (day-night), day (10 am to 5 pm) and night (6 pm to 6 am) respectively on quartz filter papers by a medium-volume sampler (model: APM 550, Envirotech, New Delhi) at flow rate: 16.6 L min-1. Two samples were collected for 24-h and one sample each for day and night time in a week to follow the weekly trends of PM2.5 and its carbonaceous aerosols .

Pipal et al., Sustain. Environ. Res., 24(2), 107-116 (2014)

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Fig. 1. Map of Agra city showing sampling site.

viz. OC and EC. There is more chance in varying the PM2.5 mass and its carbonaceous species in winter due to vehicular activities and local sources like wood, cow dung, and crop residue burning for space heating. The samples were put in polyethylene plastic bags immediately after sampling and then preserved in desiccators for subsequent measurements of mass . concentrations and OC/EC concentrations. 3.2. Quality control The sampler is designed to work at a constant flow rate of 16.7 ± 0.8 L min-1. Daily flow rate calculation (gas meter reading/timer reading) was made to make sure that the fluctuation in flow rate was within the range. Chow and Watson [14] have suggested filter change in the Wins Impactor after 72 h of sampling, but in this study filter was changed after 48 h. Periodic cleaning of the sampler was done to make the sampler . dust free. .

3.3. Gravimetric analysis Filter papers were weighed thrice before and after sampling by using microbalance (A&D, model GR202, Japan). Before weighing, the samples were .

desiccated at 20-30 °C and relative humidity (RH) of 30-40% in humidity controlled room for 24 h. The aerosol mass concentration of PM2.5 was ascertained gravimetrically by weighing the full filters before and . after the sampling. 3.4. OC/EC analysis Exposed filter papers of PM2.5 were analyzed for the concentrations of OC and EC by semi-continuous thermal/optical carbon analyzer (Sunset Laboratory Model 4L) using NIOSH 5040 (National Institute for Occupational Safety and Health) protocol [15]. Briefly, an aliquot of sample filter (2.1 cm2) is stepwise heated in a furnace up to 840 °C in a non-oxidizing atmosphere (100% He); furnace is then cooled to 550 °C and filter is stepwise heated to 850 °C in an oxidizing atmosphere (90% He, 10% O2), during each temperature step, evolved carbon is converted to methane and detected by a flame ionization detector. A calibration is performed at the end of each analysis by introducing a known amount of methane gas into the oven and measuring its constant response. The carbon evolved before the split line is considered as OC, and . that evolved after the split line is quantified as EC. .

Pipal et al., Sustain. Environ. Res., 24(2), 107-116 (2014)

RESULTS AND DISCUSSION

Meteorological parameters like wind speed (WS); wind direction (WD), RH and air temperature were measured in an automatic weather station (Envirotech WM251) which is situated approximately at 2 km away from the site. Monthly average concentration of WS was 2.5 ± 0.4 m s-1, WD 174 ± 28 degree, air temperature 16.8 ± 4.9 °C and RH 62 ± 9%. The day to day variations of meteorological parameters are shown in Fig. 2 which shows that the WD varied from 69-298 degree, RH between 48 and 87%, atmospheric temperature from 5.5-22.2 °C and WS varied from 1.34-5.32 m s-1 during the sampling periods. Higher WS (5.32 m s-1) were observed in the month of January 2012 on (4/01/2012) with WD (298 degree) whereas higher atmospheric temperature (22.2 °C) was observed in a month of February (7/02/2012) while higher RH (87%) was observed on 18/1/2012 within sampling period. Detail discussions between meteorological parameters and aerosols mass concen. tration are covered in latter section. 1.1. Concentration of PM2.5

WD Degree

X

RH %

-1

WS m s

AT °C

.

b

WD, RH

1. Meteorological Parameters

a

AT, WS

110

c

d

.

The average mass concentration of PM2.5 over study period was 183 ± 144 µg m-3 varying from 29 to 612 µg m-3 during the winter season of 2011-2012. The mean value of present study is 3-4 times higher, comparing with the National Ambient Air Quality Standards [16] given by Central Pollution Control Board, India and 7-8 times higher than World Health Organization standards [17]. Higher concentrations of PM2.5 were in the month of December (313 µg m-3) and lower in the month of February (102 µg m-3). In the month of Feb. 2012, the WS was higher (3.02 m s-1) and pollutants disperse quickly into the atmosphere. Apart from this the WD was also different in this month and was from SW direction. In December, due to low calm condition and lower temperature, higher concentration was observed. Overall higher concentrations of PM2.5 at this site may be mainly due to vehicular activities, biomass, fossil fuels, road dust and industrial effects. Duan et al. and Hsieh et al. [18, 19] have suggested that in addition to this, the fine particles may also be emitted due to more volatile organic compounds (VOC) condensing into aerosol at lower ambient temperature and more residential combustion of coal and wood for space heating during winter. In the present study, the VOC analysis was not done. During the entire study period, the large variation in PM2.5 concentrations could be due to the thermodynamic conditions in the planetary boundary layer, which either favors or adversely affects pollutants dispersion. Ambient atmospheric conditions, such as air temperature, RH and short wave radiation, could also influence the chemical reactions leading to

Sampling period

Fig. 2. Daily variations of meteorological parameters for different months. (a: Nov. 11; b: Dec. 11; C: Jan. 12 and D: Feb. 12) WS = Wind speed, RH = Relative humidity, AT = Atmospheric temperature, WD = Wind direction. .

secondary aerosol formation. Stable atmospheric conditions with low mixing height may result in significantly enhanced particulate concentrations [20]. During winter, very frequent and persistent thermal inversion and foggy conditions at ground level cause a considerable amount of aerosols to accumulate in the lower layers of the atmosphere. Aerosol concentrations during winter were also largely due to massive biomass burning over western part of India especially . Haryana and Punjab states [21]. 1.2. Concentrations of carbonaceous aerosols The monthly average concentrations of OC and EC during different time period along with some statistical information are shown in Table 1. Average concentration of OC was 58 µg m-3 for 24-h, 76 µg m-3 for day and 72 µg m-3 for night while EC was 5.2, 13 and 15 µg m-3 for 24-h, day and night, respectively. Concentration of OC varied from 39-96 µg m-3 for 24-h, 71-89 µg m-3 for day and 64-91 µg m-3 for night .

Pipal et al., Sustain. Environ. Res., 24(2), 107-116 (2014)

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Table 1. Average monthly concentration in terms of full day, during day and night separately of carbonaceous species in PM2.5 PM2.5 (ìg m-3)

OC (ìg m-3)

EC (ìg m-3)

OC/EC

24 h

Day

Night

24 h

Day

Night

24-h

Day

Night

24-h

Day

Night

Nov

162

75

97

45

71

66

3.4

14

18

13

5.2

3.6

Dec

313

239

245

96

89

91

9.3

17

15

10

5.3

5.9

Jan

179

90

120

54

72

64

3.7

8.9

13

15

8.0

4.8

Feb

102

136

102

39

72

64

4.2

13

12

9.3

5.7

5.2

Ave

189

135

141

58

76

72

5.2

13

15

12

6.1

4.9

SD

89

74

70

26

8.7

13

2.8

3.2

2.6

2.5

1.3

1.0

SD = Standard deviation

1.3. OC/EC ratios Concentrations of carbonaceous species and their ratios over Agra along with comparison with other studies carried out in other parts of the world are shown in Table 2. The OC/EC ratio is more or less uniform with relatively high values during winter, due to the change in the relative strength of their sources. For comparison OC, EC and OC/EC ratios reported over a few urban (except roadside) cities of India and other countries are also presented in Table 2. The OC, EC values reported in this study are higher than those of all other studies [18,22,25-37], but significantly lower than those of Husain et al. [28] at Lahore and Singh et al. [34] at Delhi. The concentrations of OC .

OC ìg m-3

EC ìg m-3

Concentration 24 h

a

EC

OC

Concentration day

b

c

Concentration night

while EC between 3.4-9.3, 9-17, 12-18 µg m-3 for 24-h, day and night, respectively (Fig. 3). The mass concentration of PM2.5 and its carbonaceous species viz. OC and EC are different between 24-h samples and aggregate of day and night. These differences are observed as separate samples of PM2.5 were collected in which the first two samples were taken for 24 h after that individual sample for day and night was taken per week. Higher concentration of carbonaceous aerosol species (OC and EC) at this site is due to emission from vehicular exhaust, coal combustion, biomass and fossil fuels burning, wood used in cooking, road dust [22]. The major variation in concentration of carbonaceous aerosol species was observed during 24-h sampling than day and night because of the present study being conducted at the heavy traffic site during different time periods. These variations are due to variable sources which are of local use and transported during different time periods such as EC arises from the incomplete combustion of various kinds of organic material, including coal, oil, petrol, wood and other biomass [23]. Primary organic carbon has similar sources, but it also generated from resuspension of traffic related dust and primary biogenic particles like viruses, bacteria, pollens and their fragments, fungal spores and all kinds of vegeta. tion debris [24].

Samples

Fig. 3. Concentration of carbonaceous different time periods.

species

for

and EC done in Agra in 2010 by Satsangi et al. [33] in TSP were found to be almost similar to our study for PM2.5. Carbonaceous aerosol represents a mixture of various emission sources (EC and primary OC) and secondary OC formed by atmospheric reaction processes, the ratios of OC to EC concentrations (OC/EC) can be used to evaluate emission and transportation characteristics. For example, diesel and gasoline powered vehicular exhaust exhibits OC/EC = 1-4.2 [38], residential coal smoke has OC/EC = 2.5-10.5 [39], and biomass burning with OC/EC = 7.7 [40]. In this study the average OC/EC ratios ranged from 4.9

Pipal et al., Sustain. Environ. Res., 24(2), 107-116 (2014)

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to 47 which suggests the presence of SOA. Figure 4 shows the variations in OC/EC ratios during different time periods such as 24 h, day and night respectively. It can be also concluded that the emission of OC and EC

Day

Night

OC/EC values

24

is from the variable sources in the study area, i.e., vehicular exhaust, residential coal smoke and biomass burning. The variation in the OC/EC ratios may indicate changes in emission sources, source process or source region, and EC may be considered as tracer for primary sources of carbonaceous species [9,23]. In this study much higher OC/EC ratios were observed in sample 3 for 24-h and sample 5 for night sampling (Fig. 4), probably due to the fact that sampling was done in winter during nighttime and people in this area burned wood, cow dung, and crop residue to keep warm. .

Samples

Fig. 4. OC/EC ratios during the study period.

SOA = OCtotal - Ocprimary Where (OC/EC)primary is the average primary OC/EC ratio. Depending on the nature of the measurement site, it is difficult to know the exact contribution of different primary sources without performing a detailed source analysis. However, several authors have used the OC/EC ratio to estimate the contribution of SOA to the total OC [10,27]. In this study the primary OC/EC ratio has been estimated from atmospheric data assuming either that the lowest observed OC/EC ratios represent primary aerosols [29]. Table 3 shows the month wise values of SOA and its average in the atmosphere which are calculated by using above

1.4. SOA Particulate OC has also a secondary origin from gas to particle conversion of VOCs in the atmosphere. Due to its primary character, atmospheric EC can be used as a tracer for primary OC in PM2.5 if the ratio of (OC/EC)primary for each source and the contribution of different sources at the measurement site are known [23]. The concentration of SOA in the PM2.5 can be calculated as: . .

OCprimary = (OC/EC) primary *EC

Table 2. Concentration of carbonaceous species over Northern India and their comparison with the studies done in India as well as other parts of the world (µg m-3) City Agra Ahemdabad Mumbai Hisar Dhaka

Height (m) 25 40 10 5 3

Site Roadside Urban Urban Urban -

Period

OC

EC

OC/EC

24-h

58

5.2

11.7

Day

76

13

6.1

Night

72

15

4.9

-

13

2.1

-

25 33 46

13 3.8 22

Size

Reference

PM2.5

Present study

8.3

TSP

[22]

2.0

PM10

[25]

8.5

TSP

[26]

2.1

-

[27] [28]

Lahore

12

Urban

-

110

18

5.6

PM2.5

Taiwan

5

Urban

-

15

6.1

2.4

PM2.5, PM10

[29]

Shanghai

18

Road

-

15

6.8

2.3

PM2.5

[30]

Hong Kong

-

-

-

12

3.4

3.5

PM2.5

[18]

Italy

-

-

-

9.6

1.4

6.9

[31] PM2.5

[32]

Beijing

-

Suburban

24

8.2

4.9

Agra

-

Urban

24

61

7.5

8.1

TSP

[33]

Delhi

-

Urban

-

69

39

2.2

PM10

[34]

Seattle, USA

-

Hill

-

5.7

0.9

6.1

PM2.5

[35]

Nanjing

-

-

-

13

3.7

3.6

PM2.5

[36]

Amsterdam, Netherland

-

Urban

24

5.3

1.8

2.9

PM2.5

[37]

Pipal et al., Sustain. Environ. Res., 24(2), 107-116 (2014)

equation. The value of SOA varied from 20-118 µg m-3 for 24-h, 0.1-51 µg m-3 for day and 0.1-35 µg m-3 for night respectively in the entire study period. The formation of SOA in northern Indian region is also reported by Ram and Sarin [10]. This indicates that the source of organic carbon from primary emissions as well as secondary formation in this region. SOA results from atmospheric reactions of VOCs and semi VOCs with reactive trace gases (O3, OH, NO3, NO2) followed by nucleation and/or condensation of less volatile products. The gas-phase organic carbon precursors are emitted by both natural (mainly isoprene, monoterpenes and sesquiterpenes) and anthropogenic (mainly aromatic hydrocarbons) sources [39]. Higher values of SOA during winter is due to VOC condensed into aerosol at lower temperature, as more residential combustion of coal and wood for space heating occurs in winter, and pollutants are transported from the source region such as IGP [10]. It is one of the polluted places where Ram and Sarin [10] have observed higher . OC/EC ratios. 1.5. Relationship between PM2.5 and carbonaceous species OC, EC and PM2.5 relationship gives some indications of origin of carbonaceous aerosols in the study region (Table 4). Pearson correlation for statistical analysis was performed to determine the correlation .

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among OC, EC and PM2.5 to assess the major sources of OC and EC. The correlation between PM2.5 and carbonaceous aerosols was significantly higher (r = 0.71-0.84), indicating that the contribution of OC, EC from the similar type of sources at this site while the correlation between OC and EC was determined and was also found significant (r = 0.83). The relationship between OC day versus EC day (r = 0.71) and OC night versus EC day (r = 0.28) was also found (Table 4) which indicates that the sources of OC and EC is the same and they may be from combustion of fossil fuel from traffic emission during winter season. During night time OC and EC relationship was less significant due to biomass burning and less local traffic. These interpretations were further confirmed from the measurement of OC/EC ratios during day (6.8) and . night (9.2). 1.6. Variations in OC and EC during day and night Monthly day and night mean concentrations of organic and EC are shown in Table 1. Average concentrations of OC were 76 ± 9 µg m-3 for day and 72 ± 13 µg m-3 for night whereas the concentrations of EC were 13 ± 3 and 15 ± 3 µg m-3 for day and night respectively. Average concentration of OC was higher during day time while EC was higher during night time. Also, higher OC and EC ratios during day time comparing to night time confirm that the vehicular exhaust is the .

Table 3. Values of secondary organic aerosol (SOA) Months

Time/Period

Mass (µg m-3)

OC (µg m-3)

OC/EC

SOA

November

24-h

162

45

13

35

December

24-h

313

96

10

68

January

24-h

179

54

15

42

February

24-h

102

39

9.3

26

Average

189

58

12

42

SD

89

26

2.5

18

November

Day

75

71

5.2

17

December

Day

239

89

5.3

22

January

Day

90

72

8.0

36

February

Day

136

72

5.7

22

Average

135

76

6.1

24

SD

74

8.8

1.3

8.4

November

Night

97

66

3.6

15

December

Night

245

91

5.9

49

January

Night

120

64

4.8

33

February

Night

102

64

5.2

27

Average

141

72

4.9

31

SD

70

13

1.0

14

SD = Standard deviation

Pipal et al., Sustain. Environ. Res., 24(2), 107-116 (2014)

114

dominant sources of OC and EC during day time [37]. SOA was also determined and was higher during night time samples due to stagnant and low temperature which resulted in more SOA formation in winter [20]. It was found that insignificant correlation between day-night OC-EC except day OC-EC (Table 4) inferred that the emission of carbonaceous aerosol species was from different type of sources during day and night. These variations in OC and EC concentration are observed during different time periods due to local meteorological conditions and transportation sources. . CONCLUSIONS Characteristics of mass PM2.5 and carbonaceous aerosol species were investigated at roadside in India during winter season of 2011-12. Average concentration of PM2.5 was 183 ± 114 µg m-3 varied from 29-612 ìg m-3 which is 3-4 times higher than National Ambient Air Quality Standards given by Central Pollution Control Board, India and 7-8 times higher than World health Organization standards. Carbonaceous analysis results showed that the average concentration of OC varied from 39 to 96 ìg m-3 for 24-h, 71 to 89 ìg m-3 for day and 64 to 91 ìg m-3 for night while EC varied from 3.4-9.3, 9-17, 12-18 ìg m-3 for 24-h, day and night respectively. The OC/EC ratios were observed between 4.9 and 47 which suggested the presence of SOA, SOA was higher during day time than night and 24-h samples. Mean level of SOA was 46 µg m-3 for 24-h, 27 µg m-3 for day and 35 µg m-3 for night, accounting for 73, 34 and 46% for 24-h, day and night samples of total OC. Carbonaceous aerosol account for 43% of the PM2.5 mass in which the emission of OC is 38% with EC 5%. The relative abundance of OC and EC components was higher during day time. The higher concentration of PM2.5 and associated carbonaceous aerosol species at this site is due to vehicular activities, biomass and fossil fuel combustion. There is high correlation of OC-EC with PM2.5 (r: 0.68-0.97) and OC with EC (r: 0.71-0.83) for 24-h samples. This indicates the sources of organic carbon from primary emissions as well as secondary emissions in this region. The variations in OC and EC concentration are observed during different time periods due to local meteorological conditions and transported sources. .

ACKNOWLEDGEMENTS We are thankful to University Grant Commission (RGNF-2011-12) New Delhi for financial support for this work. We are also thankful to Indian Institute Tropical Meteorology (IITM) laboratory New Delhi for analyzing the carbonaceous aerosols. . REFERENCES 1. Nel, A., Air pollution-related illness: Effects of particles. Science, 308(5723), 804-806 (2005). . 2. Ramanathan, V., P.J. Crutzen, J.T. Kiehl and D. Rosenfeld, Atmosphere - Aerosols, climate, and the hydrological cycle. Science, 294(5549), 2119. 2124 (2001). 3. Künzli, N., R. Kaiser, S. Medina, M. Studnicka, O. Chanel, P. Filliger, M. Herry, F. Horak, V. Puybonnieux-Texier, P. Quenel, J. Schneider, R. Seethaler, J.C. Vergnaud and H. Sommer, Publichealth impact of outdoor and traffic-related air pollution: A European assessment. Lancet, . 356(9232), 795-801 (2000). 4. Hong, G.B., C.M. Ma, S.Y. Liou and C.T. Chang, PM10 particulate emissions from stack flue gas in Taiwan. Sustain. Environ. Res., 22(3), 173-176 . (2012). 5. Chou, M.S. and Y.Y. Lo, Surface characteristics of particulate matter collected from industrial sources. Sustain. Environ. Res., 22(4), 225-236 . (2012). 6. Matsui, H., M. Koike, N. Takegawa, Y. Kondo, R.J. Griffin, Y. Miyazaki, Y. Yokouchi and T. Ohara, Secondary organic aerosol formation in urban air: Temporal variations and possible contributions from unidentified hydrocarbons. J. . Geophys. Res. Atmos., 114(D4), 1-22 (2009). 7. Gundel, L.A., N.S. Guyot-Sionnest and T. Novakov, A study of the interaction of NO2 with carbon particles. Aerosol Sci. Tech., 10(2), 343. 351 (1989). 8. Rogge, W.F., L.M. Hildemann, M.A. Mazurek, G.R. Cass and B.R.T. Simoneit, Sources of fine organic aerosol. 3. Road dust, tire debris and organometallic brake lining dust: Roads as sources

Table 4. Values of correlation coefficients (r) between OC, EC and other parameters PM2.5

OC 24-h

OC day

OC night

EC 24-h

EC day

EC night

OC 24-h

0.75

-

-

-

0.83

-

0.20

OC day

0.29

-

-

0.15

-

0.71

0.20

OC night

0.71

0.15

-

-

-

0.28

0.28

EC 24-h

0.84

-

-

-

-

-

-

EC day

0.68

-

-

0.25

-

-

0.25

EC night

0.07

-

-

-

-

-

-

Pipal et al., Sustain. Environ. Res., 24(2), 107-116 (2014)

9.

10.

11.

12.

13.

14.

15.

16.

17.

18.

19.

20.

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Discussions of this paper may appear in the discussion section of a future issue. All discussions should be submitted to the Editor-in-Chief within six months of publication. . Manuscript Received: February 20, 2013 Revision Received: May 27, 2013 and Accepted: June 10, 2013