107

Day and night variability of atmospheric organic and elemental carbon during winter of 2011-12 in Agra, India

1 1 2 2Atar Singh Pipal, Rohi Jan, Deewan Singh Bisht, Atul Kumar Srivastava, Suresh 2 1,Tiwari and Ajay Taneja *

1Department of ChemistryDr. B. R. Ambedkar University

Agra 282002, India2Indian Institute of Tropical Meteorology

New Delhi 110060, India

Key Words: PM , carbonaceous aerosols, secondary organic aerosol, black carbon, India 2.5

*Corresponding authorEmail: ataneja5@hotmail.com

ABSTRACT

INTRODUCTION

The mass concentrations of organic carbon and elemental carbon (OC and EC) associated with PM were investigated at a traffic influenced site (roadside) Kandhari, U.P. India during winter of 2.5

2011-12 by semi-continuous carbon analyzer. Individual samples of PM were collected for different 2.5

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 PM was 183 ± 114 µg 2.5

-3 -3m and varied from 29 to 612 µg m . Carbonaceous analysis results showed that the average concen--3 -3 -3tration of OC varied from 39 to 96 µg m for 24-h, 71 to 89 µg m for day and 64-91 µg m for night

-3while EC varied from 3.4-9.3, 8.9-16.8, 12.4-18.2 µg m for 24-h, day and night samples respec-tively. 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 PM mass in which the 38% OC 2.5

and 5% EC contributed to total PM concentration. Day and night variation of carbonaceous aerosol 2.5

was also studied and was found that the relative abundance of OC and EC was higher during day time. The high concentration of PM and its associated carbonaceous aerosol species at this site may 2.5

be due to vehicular activities, biomass and fossil fuel combustion. Strong correlation between OC, EC and PM (r = 0.83-0.97) was observed for 24-h samples. Average level of secondary organic 2.5

-3 -3 -3carbon was 46 µg m for 24-h, 27 µg m for day and 35 µg m 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. .

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 ambi-ent 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

particulate pollutants in Austria, France and Switzer-land were found to cause 40,000 premature deaths, 25,000 new cases of chronic bronchitis and many chronic bronchitis episodes and asthma attacks. More-over, 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 com-pounds that can be classified into aliphatic, aromatic compounds, acids, etc and is formed from various

.

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

108

sources (e.g., combustion, industrial, and natural sources) and complex atmospheric processes (direct emission, homogenous gas-phase oxidation, gas-aerosol 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 un-known 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 en-hancing catalytic processes. EC may involve in some important chemical reactions involving atmospheric sulfur dioxide (SO ), nitrogen oxides (NOx), ozone 2

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 proc-esses (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 atmos-phere [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 roadsidewhich 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 anthropo-genic 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 consider-ing 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 PM in terms of carbonaceous 2.5

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 inhab-itants and the population density is about 21,150

-2persons km with 386,635 vehicles registered and 32,030 generator sets. In Agra, 60% pollution is mainly due to vehicular emissions from three national high-ways (NH-2, NH-3 and NH-11) cross the city. Pipal et al. [11] have reported a high density of vehicular

5 -1traffic (10 vehicles d ) on these three highways.

2. Sampling Site

PM samples were collected from a roadside i.e., 2.5

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.

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3. Sampling and Analysis

3.1. Sampling

Aerosol samples of PM were collected on the 2.5

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,

-1Envirotech, New Delhi) at flow rate: 16.6 L min . 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 PM and its carbonaceous aerosols 2.5

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

109

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

viz. OC and EC. There is more chance in varying the PM mass and its carbonaceous species in winter due 2.5

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 -1rate of 16.7 ± 0.8 L min . 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 GR-202, Japan). Before weighing, the samples were

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.

desiccated at 20-30 °C and relative humidity (RH) of 30-40% in humidity controlled room for 24 h. The aerosol mass concentration of PM was ascertained 2.5

gravimetrically by weighing the full filters before and after the sampling.

3.4. OC/EC analysis

Exposed filter papers of PM were analyzed for 2.5

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,

2an aliquot of sample filter (2.1 cm ) 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 oxi-dizing atmosphere (90% He, 10% O ), during each 2

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.

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

110

Fig. 2.

RESULTS AND DISCUSSION

1. Meteorological Parameters

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

-1WS was 2.5 ± 0.4 m s , WD 174 ± 28 degree, air tem-perature 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

-11.34-5.32 m s during the sampling periods. Higher -1WS (5.32 m s ) 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 PM 2.5

The average mass concentration of PM over 2.5-3study period was 183 ± 144 µg m varying from 29 to

-3612 µg m 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

-3PM were in the month of December (313 µg m ) and 2.5-3lower in the month of February (102 µg m ). In the

-1month of Feb. 2012, the WS was higher (3.02 m s ) 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 PM at this site may be mainly due 2.5

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 PM concentrations could be due to the 2.5

thermodynamic conditions in the planetary boundary layer, which either favors or adversely affects pollu-tants dispersion. Ambient atmospheric conditions, such as air temperature, RH and short wave radiation, could also influence the chemical reactions leading to

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.

.

secondary aerosol formation. Stable atmospheric conditions with low mixing height may result in sig-nificantly 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 concen-trations 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

-3 -3concentration of OC was 58 µg m for 24-h, 76 µg m -3 for day and 72 µg m for night while EC was 5.2, 13

-3 and 15 µg m for 24-h, day and night, respectively. -3Concentration of OC varied from 39-96 µg m for

-3 -3 24-h, 71-89 µg m for day and 64-91 µg m for night

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

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. .

WD

, RH

-1 WD Degree RH % WS m s AT °C

Sampling period

AT

, WS

a

b

c

d

X

111

Table 1. Average monthly concentration in terms of full day, during day and night separately of carbonaceous species in PM 2.5

-3 while EC between 3.4-9.3, 9-17, 12-18 µg m for 24-h, day and night, respectively (Fig. 3). The mass concen-tration of PM and its carbonaceous species viz. OC 2.5

and EC are different between 24-h samples and aggregate of day and night. These differences are observed as separate samples of PM were collected 2.5

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 con-centration of carbonaceous aerosol species was ob-served 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].

1.3. OC/EC ratios

Concentrations of carbonaceous species and theirratios 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

.

.

and EC done in Agra in 2010 by Satsangi et al. [33] in TSP were found to be almost similar to our study for PM . Carbonaceous aerosol represents a mixture of 2.5

various emission sources (EC and primary OC) and secondary OC formed by atmospheric reaction proc-esses, 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

SD = Standard deviation

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

Nov

Dec

Jan

Feb

Ave

SD

24 h

162

313

179

102

189

89

Day

75

239

90

136

135

74

Night

97

245

120

102

141

70

24 h

45

96

54

39

58

26

Day

71

89

72

72

76

8.7

Night

66

91

64

64

72

13

24-h

3.4

9.3

3.7

4.2

5.2

2.8

Day

14

17

8.9

13

13

3.2

Night

18

15

13

12

15

2.6

24-h

13

10

15

9.3

12

2.5

Day

5.2

5.3

8.0

5.7

6.1

1.3

Night

3.6

5.9

4.8

5.2

4.9

1.0

-3PM (ìg m )2.5

-3 OC (ìg m ) -3EC (ìg m ) OC/EC

Fig. 3. Concentration of carbonaceous species for different time periods.

C

once

ntra

tion

24

h

Con

cent

rati

on d

ay

Con

cent

rati

on n

ight

-3 OC ìg m -3EC ìg m

EC

a

b

c

OC

Samples

112

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 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 in-dicate 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.

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 PM if the ratio of 2.5

(OC/EC) for each source and the contribution of primary

different sources at the measurement site are known [23]. The concentration of SOA in the PM can be 2.5

calculated as:

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

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

City

Agra

Ahemdabad

Mumbai

Hisar

Dhaka

Lahore

Taiwan

Shanghai

Hong Kong

Italy

Beijing

Agra

Delhi

Seattle, USA

Nanjing

Amsterdam, Netherland

Height (m)

25

40

10

5

3

12

5

18

-

-

-

-

-

-

-

-

Site

Roadside

Urban

Urban

Urban

-

Urban

Urban

Road

-

-

Suburban

Urban

Urban

Hill

-

Urban

Period

24-h

Day

Night

-

-

-

-

-

-

-

-

-

24

24

-

-

-

24

OC

58

76

72

13

25

33

46

110

15

15

12

9.6

8.2

61

69

5.7

13

5.3

EC

5.2

13

15

2.1

13

3.8

22

18

6.1

6.8

3.4

1.4

4.9

7.5

39

0.9

3.7

1.8

OC/EC

11.7

6.1

4.9

8.3

2.0

8.5

2.1

5.6

2.4

2.3

3.5

6.9

8.1

2.2

6.1

3.6

2.9

Size

PM2.5

TSP

PM10

TSP

-

PM2.5

PM , PM2.5 10

PM2.5

PM2.5

PM2.5

TSP

PM10

PM2.5

PM2.5

PM2.5

Reference

Present study

[22]

[25]

[26]

[27]

[28]

[29]

[30]

[18]

[31]

[32]

[33]

[34]

[35]

[36]

[37]

OC = (OC/EC) *ECprimary primary

SOA = OC - Octotal primary

Where (OC/EC) is the average primary OC/EC primary

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 atmos-pheric 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

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

Samples

OC

/EC

val

ues

24 Day Night

113

-3 equation. The value of SOA varied from 20-118 µg m-3 -3 for 24-h, 0.1-51 µg m for day and 0.1-35 µg m for

night respectively in the entire study period. The for-mation of SOA in northern Indian region is also re-ported 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 (O , OH, NO , NO ) followed 3 3 2

by nucleation and/or condensation of less volatile products. The gas-phase organic carbon precursors are emitted by both natural (mainly isoprene, monoter-penes 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 com-bustion 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 PM and carbonaceous 2.5

species

OC, EC and PM relationship gives some indica-2.5

tions of origin of carbonaceous aerosols in the study region (Table 4). Pearson correlation for statistical analysis was performed to determine the correlation

.

.

Table 3. Values of secondary organic aerosol (SOA)

Months

November

December

January

February

November

December

January

February

November

December

January

February

Time/Period

24-h

24-h

24-h

24-h

Average

SD

Day

Day

Day

Day

Average

SD

Night

Night

Night

Night

Average

SD

-3Mass (µg m )

162

313

179

102

189

89

75

239

90

136

135

74

97

245

120

102

141

70

-3OC (µg m )

45

96

54

39

58

26

71

89

72

72

76

8.8

66

91

64

64

72

13

OC/EC

13

10

15

9.3

12

2.5

5.2

5.3

8.0

5.7

6.1

1.3

3.6

5.9

4.8

5.2

4.9

1.0

SOA

35

68

42

26

42

18

17

22

36

22

24

8.4

15

49

33

27

31

14

SD = Standard deviation

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

among OC, EC and PM to assess the major sources 2.5

of OC and EC. The correlation between PM and 2.5

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 concen-

-3trations of OC were 76 ± 9 µg m for day and 72 ± 13 -3µg m for night whereas the concentrations of EC were

-313 ± 3 and 15 ± 3 µg m 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

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.

114

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

OC 24-h

OC day

OC night

EC 24-h

EC day

EC night

PM2.5

0.75

0.29

0.71

0.84

0.68

0.07

OC 24-h

-

-

0.15

-

-

-

OC day

-

-

-

-

-

-

OC night

-

0.15

-

-

0.25

-

EC 24-h

0.83

-

-

-

-

-

EC day

-

0.71

0.28

-

-

-

EC night

0.20

0.20

0.28

-

0.25

-

CONCLUSIONS

Characteristics of mass PM and carbonaceous 2.5

aerosol species were investigated at roadside in India during winter season of 2011-12. Average concentra-

-3tion of PM was 183 ± 114 µg m varied from 29-612 2.5 -3ìg m 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

-3 -3 varied from 39 to 96 ìg m for 24-h, 71 to 89 ìg m for -3 day and 64 to 91 ìg m for night while EC varied from

-3 3.4-9.3, 9-17, 12-18 ìg m 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

-3samples. Mean level of SOA was 46 µg m for 24-h, -3 -327 µg m for day and 35 µg m 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 PM mass in which the emission of OC is 38% 2.5

with EC 5%. The relative abundance of OC and EC components was higher during day time. The higher concentration of PM and associated carbonaceous 2.5

aerosol species at this site is due to vehicular activities, biomass and fossil fuel combustion. There is high correlation of OC-EC with PM (r: 0.68-0.97) and OC 2.5

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 meteoro-logical 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. .

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Discussions of this paper may appear in the discus-sion section of a future issue. All discussions shouldbe submitted to the Editor-in-Chief within six monthsof publication. .

Manuscript Received: Revision Received:

and Accepted:

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