IASTA-2010

F–O–1

Seasonal and Diurnal Variation in Black Carbon Concentrations over Darjeeling

A. Adak, A. Chatterjee* S. K. Ghosh, S. Raha and A.K. Singh

Bose Institute,Kolkata (* Presently at National Atmospheric Research Laboratory, Gadanki)

Introduction

The increasing consumptions of fossil fuels and bio-fuels, i.e., the conventional energy sources, increase the emissions of carbonaceous aerosols, which affect the air quality and regional climate (Parashar et al., 2005). They directly reduce the incoming shortwave solar radiation, leading to the heating of atmosphere. Whereas, at surface they give cooling effect, thus changing possibly the temperature structure in the troposphere which in turn affects the cloud micro physical properties and thereby rainfall mechanism (Menon et al., 2002).

In the present study, seasonal and diurnal variations of BC during Jan-Dec have been discussed in relation to changing meteorological conditions and changes in the local boundary layer through day and night throughout the year along with the variation in several anthropogenic activities.

Methodology

The data of black carbon concentrations were collected using an Aethelometer (Model AE-21, Magee scientific, USA) during Jan-Dec’2008. The measurements were based on the attenuation of light through the quartz filter tape onto which the aerosol particles are made to impinge. The attenuation is proportional to the surface concentration of black carbon.

Results

The monthly variation of BC shows the higher concentration during winter followed by summer, postmonsoon and premonsoon with the minimum during monsoon. The winter shows ~1.5 times higher in concentration than premonsoon and postmonsoon while it was ~10 times higher than monsoon. The diurnal variation of BC in different seasons during the entire study period is shown in Fig 1. It is observed that, the concentrations of BC peaked up during morning (0900 hrs LT) hours and remained higher till early afternoon (1300 hrs LT).

During evening (1700 hrs LT) it shows another peak in the dry season. The evening peaks during summer and postmonsoon were found to be dominant compared to morning peaks due to massive influx of tourists during evening. In winter, BC shows much higher concentrations during late evening (1900 hrs LT) to night (2100 hrs). Monsoon shows much lower concentrations compared to dry seasons.

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Figure 1. Mean diurnal variations in BC concentrations (ng m-3) in different seasons.

The monthly variation of ratio of day-time to night-time BC concentration is shown in Fig 2. The ratio was found to be higher than the annual mean ratio in all the months except winter. This could be due to massive burning activities to get warmth against cold during night in winter months whereas in rest of the months, the more prevalence of sources (vehicular, domestic, industrial activities etc) enhanced the ratio value.

Figure 2. The monthly variation in ratio of Day-time to night-time BC concentrations

However, other than the anthropogenic activities (vehicular, domestic and industrial), the accumulation of sub micron BC particles within the nocturnal boundary layer during night and its breaking up with the advancement of the day also governed the diurnal variaon of BC.

References

Menon, S., Hansen, J., Nazaren, Ko, L. and Leo, Y (2002), Climate effects of BC aerosols in China and India. Science, 297, 2250–2253.

Parashar D.C., R. Gadi, T.K. Mandal and A.P. Mitra (2005), Carbonaceous aerosol emissions from India, Atm. Environ., 39, 7861–7871.

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F–O–2

Carbon Profile of PM2.5 Aerosol in Mumbai City

Abba Elizabeth Joseph#, Seema Unnikrishnan# and Rakesh Kumar*

# National Institute of Industrial Engineering, Vihar Lake, Mumbai -400087 Email : abba1@rediffmail.com, seemaunnikrishnan@gmail.com

* National Environmental Engineering Research Institute, 89/B, Dr. A.B. Road, Mumbai -400018 Email : rakeshmee@rediffmail.com

Introduction

Air quality management in the India is being studied with more rigor than before. Country has also progressed much in understanding criteria (TSP, PM10, SO2, NO2, NH3, Pb, CO) pollutants in outdoor environment with nation wide network of National ambient air quality monitoring stations. Ambient air quality standard are also in place for the above pollutants. Over the years worldwide, focus on TSP has shifted to PM10 and then to fine particles (PM2.5) in urban areas because they are a major health and environmental concern. “The epidemiological, physiological, and toxicological evidence suggests that fine particles (indicated by PM2.5) play a substantial role in affecting human health. These fine particles can be breathed deeply into the lungs, penetrate into indoor environments, remain suspended in the air for long periods of time, and are transported over long distances, resulting in relatively ubiquitous exposures” (Pope and Dockery, 2006). Fine particles are largely generated, directly or indirectly, by combustion processes and are relatively complex mixtures (Pope and Dockery, 2006). The sources of fine, combustion-derived pollutants are less well understood for India. Elemental Carbon (EC) has primary source of emissions and is often used as a tracer for diesel exhaust particles (Götschi et al., 2002), whereas Organic Carbon (OC) can be emitted from primary emission sources and generated from chemical reactions among primary gaseous organic carbon species in the atmosphere (Kim et al., 2000) TERI, 2001 has pointed out that in India very few studies have analyzed carbon fraction, limiting the ability to understand combustion sources.

Study Objective

z To study spatial variance of PM2.5 concentration outdoor environment of Mumbai city.

zTo quantify and characterize eight carbonaceous fraction (OC1 ,OC2, OC3, OC4, EC1 EC2, EC3, OP, in PM2.5 )

zTo estimate secondary organic carbon formation.

The present study attempts to monitor outdoor fine particles at four sites control(C), kerb(K), residential(R) and industrial(I) in Mumbai city, India during summer, post - monsoon and winter season for 15 days in each season during year 2007-2008. PM2.5

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along with various fraction of Elemental carbon (EC1, EC2, EC3), Organic (OC1, OC2, OC3, OC4, OP) and Total Carbon were analyzed for all four sites. These parameters provide an insight into the types of combustion products and possible sources.

Sample Collection and analysis

The fine particles were simultaneously measured using MiniVol PM2.5 Sampler (Make : Air Metrics) at the rate of 5 liters per minute for 24 hours on Whatman PTFE, PP Ring Supported: Teflon Filters (46.2 mm and 2.0 μm Pore Size) and Pallflex Tissue Quartz filters, 47 mm. In the particulate matter-sampling mode, air is drawn through a particle size separator and then through a filter medium. Particle size separation is achieved by impaction. The Teflon filters were equilibrated at 20oC and 40% RH in a temperature and humidity controlled clean room chamber for 24 hours before and after sampling. The particulate mass on Teflon filter was determined by weighing on an electronic microbalance (Make: Sartorious, Model ME5) with 1 g sensitivity. Each filter was weighed in duplicate before and after sampling and average weight was considered. Microbalance was daily tested with NIST calibrated weights of 100 and 200 mg to check the performance. The quartz filters were preheated at 900oC for 3 hours before monitoring to remove any background organics in the filter. The filters were kept and heated in silica crucibles covered on top with another silica crucible. After air sampling loaded filters were stored in a freezer at –20oC to prevent the evaporation of volatile compounds until analysis. The DRI thermal optical analyzer was used for measuring Organic carbon (OC) and Elemental carbon (EC). This method is based on preferential oxidation of organic carbon and elemental carbon compounds at different temperatures. The principal function of the optical component of the analyzer is correction for pyrolysis of organic carbon. The eight fractions OC1, OC2, OC3, OC4, EC1, EC2, EC3 and OPC (Pyrolyzed Organic Carbon) are reported. The IMPROVE protocol defines OC as OC1+OC2+OC3+OC4+OPC and EC as EC1+EC2+EC3-OPC. A filter punch is submitted to volatilization at temperatures of 120, 250, 450, and 550 degree C in a 100% helium atmosphere, then to combustion at temperatures of 550, 700, and 800 degree C in 2% oxygen and 98% helium atmosphere (DRI, 2000). A 0.526 cm2 ample aliquot of the filter was subjected to carbon analysis. The analyzer was calibrated with known quantities of carbon dioxide. Replicate analyses were performed at the rate of 1 per 10 samples. The precision was within 5 percent for Total carbon.

Results and Discussion

Outdoor concentration of PM2.5 mass and carbon content at four sites, season wise is presented in the Table 1. The average concentration of fine particles at control, kerbsite, residential and industrial area was 74±13.91, 86±27.12, 88±36.97, 95±25.85 μg/m3 . The ambient PM2.5 concentrations exceeded USEPA 24 hourly standard of 35 μg/m3 and 60 μg/m3-proposed standards for India at all sites indicating unhealthy air quality. The average concentration of OC at C, K, R and I sites in was 19.9±6.11, 28.1±14.17, 31.2±14.48 and 29.2±15.12 μg/m3 while the corresponding EC concentration was 5.2±2.12, 8.9±3.08, 7.8±4.33 μg/m3 , and 7.0±3.19 respectively. Possible sources around ambient sites include vehicles, industries, sea spray, biomass burning, road dust, bakeries, open eat out etc. The average annual OC contributions in PM2.5 at C, K, R and I sites outdoors were 27%, 32%, 35% and 29%. On the other hand, for the same sites outdoor EC contributions were 7%,

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10%, 8% and 7% respectively. The OC contribution was highest at R, possible sources include vehicles include vehicles, bakeries, biomass burning etc whereas EC concentration was high at K due to heavy duty vehicles and intercity buses plying on arterial road.

Eight Carbon Fraction in PM2.5

The carbon fraction abundances in a source category may be useful for source discrimination Chow et al., 2004. The temperature resolved fractional carbon data can be utilized to enhance source apportionment study, especially with respect to the separation of diesel emissions from gasoline vehicles.The average percentage of OC and EC in TC was 80% and 20%, except kerbsite were OC and EC was 76% and 24%. The eight fractions are in the order of increasing volatility (the OC fractions), as the method only differentiates by volatility (EC being nonvolatile). OC1 compounds are more likely to be VOCs that are adsorbed by the filter matrix while OC2 and OC3 are semi-volatile compounds of increasing molecular weights. The percentage abundance of different OC and EC fraction in TC was in the order of EC1>OC2>OC3>OP>OC4>OC1>EC2>EC3 except for OC2 fraction greater than EC1 at residential area.Highest percentage of OC in TC was observed at Industrial site, where EC percentage in TC was estimated high at Kerbsite.

EC1 percentage in TC was highest at kerbsite outdoor.EC1 is the soot commonly seen in urban atmosphere, it includes both automotive and some diesel soot. Difference in the carbon composition of source profiles for diesel and gasoline powered vehicles studied by Watson et al., 1994 indicated that EC1 in the gasoline-fueled sample is larger, whereas EC2 is most abundant in exhaust of diesel fuel vehicles, as compared to gasoline fuel vehicles. Fuel emission survey has indicated that in Mumbai the percentage of vehicles on petrol are 59% and 41% on diesel respectively (NEERI, 2009). EC2 was 2 -2.5% in TC at all sites sites. In general EC2 and EC3 are much smaller than EC1. There was very little high temperature EC3 and this could be due to carbonates present in the road dust.

As per IMPROVE protocol Organic carbon evolved from the filter punch in a He only atmosphere at 120oC is defined as VOC. The percentage of OC1 in TC was 3-4% in TC outdoor. High percentage of VOCs at kerbsite is due to vehicles. Percentage of OC2 fraction in TC was 25-32%, OC3 in TC was 20-22%. Cao et al., 2004; 2006 indicated that high OC2 and OC3 is associated with presence of gasoline and LPG emissions and secondary organic carbon. The Pyrolyzed Organic Carbon (OP) in TC was 12-16 %. OP is associated with water soluble organic carbon (Cao et al., 2004).

Secondary Organic Carbon

Since secondary organic aerosol cannot be detected directly, particulate OC to EC ratios exceeding 2.0 have been used to identify Secondary Organic Carbon (SOC) formation (Chow et al., 1996). Lowest OC/EC ratios contain exclusively primary carbonaceous compounds (Na et al., 2004). Turpin and Huntzicker, 1995; used the following equation to estimate Secondary Organic Carbon:

SOC= OCtot – EC (OC/EC)min

SOC= Secondary Organic Carbon, OCtot= Total organic carbon in the sample EC= Elemental carbon, (OC/EC)min= min ratio observed in all sample

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The OC/EC ratio in outdoor environment at all the sites was greater than 2 with average ratio of 3.83, 3.16, 3.99, and 4.16 at Control, Kerbsite, Residential and Industrial respectively). The ratio >2 implies that SOC is formed in Mumbai city besides primary carbon emission sources.

The average SOC concentration at C, K, R and I outdoor was 9.0±3.82, 12±10.82, 16±5.34, and 10±5.28 μg/m3 accounting for 48%, 37%, 54% and 33%. Correlation coefficient was estimated between EC and SOC concentration. Good correlation R2=0.54 was observed at kerbsite indicating primary organic formation due to presence of fresh emission from vehicles. More research is needed on OC/EC ratio and SOC for Indian cities to better understand their formation mechanism.

Table 1. Carbon concentration in PM2.5 at Mumbai city during 2007-2008, units: μg/m3

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Conclusions

An attempt was made to assess the status of ambient PM2.5 levels along with their composition with regard to Elemental Carbon and Organic Carbon for four different land use pattern in Mumbai City. The ambient PM2.5 concentrations exceeded USEPA 24 hourly standard of 35 μg/m3 and 60 μg/m3-proposed standards for India at all sites indicating unhealthy air quality.

The average percentage of OC and EC in TC was 80% and 20%, except kerbsite were OC and EC was 75% and 25% at outdoors The ratio >2 implies that SOC is formed in Mumbai city indicating that contribution to carbonaceous fraction besides primary emission sources. More research is needed on OC/EC ratio and SOC for Indian cities to better understand their formation mechanism.

References

1.Pope, C. A. and Dockery, D. W. (2006) Health Effects of Fine Particulate Air Pollution: Lines that Connect”, J. Air Waste Manage. Assoc., 56, 709-688

2.Götschi, T., Oglesby, L., Mathys, P., Monn, C., Manalis, N., Koistinen, K.,, Jantunen, M., Hänninen, O.,

Polanska, L. and Künzli, N. (2002) Comparison of Black Smoke and PM2.5 Levels in Indoor and Outdoor Environments of Four European Cities, Environ. Sci. Technol., 36, 1191–1197

3.Kim, Y.P., Moon, K.C., Lee, J.H. and Baik, N.J. (2000) Organic and Elemental Carbon in Fine Particles at Kosan, Korea, Atmos. Environ., 34, 3309-3317

4.The Energy and Resources Institute (2001) Resource Review of Past and On-Going Work on Urban Air Quality in India, The World Bank

5.Chow, J.C., Watson, J.G., Kuhns, H., Etyemezian, V., Lowenthal, D.H., Crow, D., Kohl, S. D., Engelbrecht, J. P., Green, M. C. (2004) Source Profiles for Industrial, Mobile, and Area Sources in the Big Bend Regional Aerosol Visibility and Observational Study, Chemosphere, 54, 185-208

6.Watson, J.G., Chow, J.C., Lowenthal, D.H., Pritchett, L.C., Frazier, C.A., Neuroth, G.R. and Robbins, R. (1994) Differences in the Carbon Composition of Source Profiles for Diesel- and Gasoline Powered Vehicles. Atmos. Environ., 28, 15:2493-2505

7.NEERI (2009) Report on Air Quality Assessment, Emissions Inventory & Source Apportionment Studies: Mumbai

8.Cao, J.J., Lee, S.C., Ho, K.F., Zou, S.C., Fung, K., Li, Y., Watson, J. G. and Chow, J C. (2004) Spatial and Seasonal Variations of Atmospheric Organic Carbon and Elemental Carbon in Pearl River Delta Region, China, Atmos. Environ., 38, 4447-4456

9.Cao, J.J., Lee, S.C., Ho, K.F., Fung, K., Chow, J. C., Watson, J G. (2006) Characterization of Roadside Fine Particulate Carbon and its Eight Fractions in Hong Kong, Aerosol and Air Quality Research, 6, , 106-122

10.Chow, J.C., Watson, J.G., Lu, Z., Lowenthal, D.H., Frazier, C.A., Solomon, P.A., Thuillier, R.H. and

Magliano, K. (1996) Descriptive Analysis of PM2.5 and PM10 Regionally Representative Locations During SJVAQS /AUSPEX, Atmos. Environ., 30:2079 –2112

11.Na, K., Sawant, A.A., Song, C., Cocker D.R. (2004) Primary and Secondary Carbonaceous Species in the Atmosphere of Western Riverside County, California, Atmos. Environ., 38, 1345-1355

12.Turpin, B.J., Huntzicker, J.J., Larson, S.M., Cass, G.R. (1991) Los Angeles Summer Midday Particulate Carbon; Primary and Secondary Aerosol. Environ. Sci. Technol., 25, 1788-1793

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F–O–3

Water Soluble Carbonaceous Species in Particulate Matter

(PM10) of Mumbai

Abhaysinh Salunkhe#+ , Sugandha Shetye+, Rakesh Kumar# , Indrani Gupta#, Abba Elizabeth#*, Seema Unnikrishnan* and Sagar Marathe*

# National Environmental Engineering Research Institute, Mumbai Zonal Laboratory,Worli, Mumbai-18.

+ K.J.Somaiya College of Science & Commerce, Vidhyavihar, Mumbai-77. *National Institute of Industrial Engineering, Vihar Lake, Mumbai-87

abhay.salunkhe@rediffmail.com,rakeshmee@rediffmail.com,indranig1@rediffmail.com, abba1@rediffmail.com

Introduction

Mumbai, the commercial and industrial capital of India with a population of 12.1 million has been under stress due to increasing urbanization. Though industries are declining, in the city still 40 air polluting small and large scale industries are operating. On the other hand, large increase in vehicle numbers in last few years has not only added city traffic problems but also higher emission. Other than biomass burning, poor road conditions, commercial and domestic cooking are some of the major contributory sources for particulate emission in city.

In Particulate Matter, species such as PAHs, Organic Carbon (OC), Elemental or Black Carbon (EC or BC) have been identified as tracers of anthropogenic sources. It has been found that Organic species are good tracers of emission sources. Water-soluble organic compounds (WSOC) potentially play an important role in aerosol–cloud interaction, and are contributors to cloud condensation nuclei (CCN). The ability of water-soluble organic particles to act as CCN has been explained on the basis of both the hygroscopic and surface-active properties of water-soluble organic compounds, which in turn depend on their chemical composition (Decesari et al., 2005). WSOC include dicarboxylic acids, Ketocarboxylic acids, dicarbonyls, carbohydrates, amino acids, aliphatic amines, urea, and some miscellaneous multifunctional compounds containing multiple hydroxyl, carboxyl, and carbonyl groups (Bao, et al., 2009). As oxidized species, WSOC aerosols may derive from direct emissions (e.g., automobile exhaust, fossil fuel combustion, biomass burning) or from photochemical oxidation of organic precursors of both anthropogenic and biogenic origin (Kawamura and Yasui et al., 2005; Hsieh et al., 2007). In present study, an attempt has been made to quantify Water Soluble total Carbon (WSTC) in terms of Water Soluble Organic Carbon (WSOC) and Water Soluble Inorganic Carbon (WSIC) in PM10 mass in Mumbai.

Sampling Locations and Experimental Methodology

PM10 was measured at four different locations, which were categorized as Control site

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(Colaba), Kerb cum Commercial site (Dadar), Residential site (Khar) and Industrial site (Mahul) during different season viz. summer, Post Monsoon and winter of 2007-2008. PM10 was collected on a glass fiber filter (8X10"pall life science GF/A) using Envirotech Respirable dust Sampler (Model APM460NL). The collected mass was first analyzed gravimetrically and later for the water-soluble carbon. Known area of exposed filter paper was subjected to extraction using ultra pure distilled water with low dissolved carbon in ultrasonic bath for 60 minutes. The extract was filtered using the Teflon syringe filters and final volume was made up to 50ml by ultra pure water. Extracted samples were preserved at 40C to avoid any volatilization loss and microbial contamination. Samples were subjected to analyze for Total carbon (TC) and Inorganic carbon (IC) in terms of soluble Carbonate (-CO3-2) and Bicarbonate (-HCO3-1) using TOC Analyzer (Model-TOC-V CSH/CSN, Shimadzu, Japan). Purified Air (O2: 20 +1%) was used as carrier gas. It is the Thermal Catalytic Oxidation Method where samples are subjected to heating and converted into CO2 gas that is finally detected by NDIR detector (Karthikeyan et al., 2005).

Results

Figure 1 gives the average concentration of PM10, SO2, NOX and Carbonaceous Species at four sites of Mumbai. Mass concentration of PM10 was found to be very high at all sites during the winter season. Among all the four, values of mass PM10 during Winter period was higher at Khar (250μg/m3) followed by Mahul (225 μg/m3) Dadar (199μg/m3) and lower site at Colaba (170μg/m3).Except Mahul, concentration at all other three sites were within the CPCB standard of 100 μg/m3 for rural residential and mix use area during the Summer season.

PM10

std 100

g/m3

for 24

SO2

and Nox

Std. 80

g/m3

for 24

Figure 1. Seasonal Variation of Avg. Water soluble carbonaceous species with PM10, SO2 and NOX conc

During post monsoon, PM10 values were found to be highest at Mahul (203μg/m3) and in winter Khar (250 μg/m3) showed the highest values. Being the control site, Colaba shows low values of PM10 in all three seasons. SO2 was within the CPCB standard (80μg/

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m3) at all sites in all the three seasons. NOX concentrations were also within the CPCB standard of 80μg/m3 except at Dadar and Mahul during winter season. Carbonaceous species are together considered as water soluble total carbon (WSTC) which is sum of WSOC and WSIC. From the seasonal analysis of WSOC and WSIC, there is similar variation in their concentration as observed for the PM10. WSOC values increases from summer to winter. In summer season, a maximum value was observed at Colaba (2.264μg/m3) whereas during Post Monsoon and winter maximum was at Khar (9.224μg/m3), (10.326μg/m3) respectively. Formations of secondary organic aerosols (SOA) are the major contributory sources for WSOC, as SOA formation leads to increase in polarity of these groups of compound towards water. Along with this, WSOC particle is part of OC fractions that are directly emitted from sources such as fossil fuel combustion, biomass burning, industrial emissions, along with the natural source such as soil. Soil is enriched with organic matter (OM) in the form of various biological molecules and some complex carbon compounds such as Humic Acid and Fulvic acids. They are also termed as HULIS i.e.Humic Like Substances (Graber.E and Rudich Y et al., 2006). Whereas WSIC i.e. water soluble inorganic carbon is considered as soluble carbonate and bicarbonate which are basically originated from soil. Usually they exist in soil with some inorganic ionic species such as Ca+2 and Mg+2 to form their respective carbonate and bicarbonate molecules. At all sites, concentrations of WSOC were significantly higher than WSIC as their emission sources are unequally distributed in the study area.

Pearson correlation matrix

Pearson correlation matrix between the monitored PM10 and WSOC-WSIC was obtained as given in Table1.It shows some significant correlation between PM10 and Carbon content at all four sites.

Table 1. Correlation matrix for four locations.

Note: *Correlation is significant at the 0.05 level (2-tailed). **Correlation is significant at the 0.01 level (2- tailed).

As evident from Table 1, high correlation of WSOC vs.PM10 indicate that WSOC may be directly emitted from the primary sources such as biomass burning and in the form of

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Secondary Organic Aerosol. In the atmospheric reaction, organic compounds emitted from various sources undergo photoxidation reactions with other existing organic and inorganic pollutants, resulting into the formation of polar organic molecules that are categorized as SOA. It commonly includes water-soluble organic compounds/carbon. Major contributing sources for organic carbon emission in PM10 fraction are based on combustion origin which includes vehicular exhaust, biomass combustion, residual oil burning, commercial and domestic cooking activity, coal burning and industrial emissions. WSOC also originates from resuspended soil.

Soil contributes in WSOC in the form of HULIS. From high correlation of WSOC vs. PM10, at Khar, Dadar and Colaba it can be concluded that, primary emission sources such as biomass burning along with the mechanism of SOA formation could be major contributors of WSOC in PM10. In case of industrial site, Mahul has high emissions in the form of particulate and hydrocarbons the later come from petroleum refineries, along with above mentioned sources which are scattered at all locations. Significant correlation of PM10 vs. SO2 at all sites shows biomass combustion in terms of wood and coal as the dominant sources of PM10 emission. In case of WSOC vs. NOX, significant correlation was observed at Khar, Mahul, Dadar and Colaba, which implies that vehicular traffic is one of the dominant sources of NOX emission. HC emission from diesel and CNG vehicles at all sites can also be considered indirectly responsible for WSOC formation. These emitted organic pollutants which undergo various photo oxidation reactions could result in SOA formation, which again contribute to WSOC. Apart from this, very weak correlation of WSOC vs. WSIC at all sites show that WSOC and WSIC may not be released from single dominant primary sources and there may be formation of secondary organic aerosol.

Conclusions

To understand the most probable emission sources of PM10, it is very vital to measure the OC, EC and water soluble carbons. From the correlation matrix of WSOC, PM10, SO2, NOX and WSIC, we observed that contribution of WSOC in PM10 is significant. In case of Mumbai city, contribution of WSOC in PM10 is because of two major possible sources. One of the most possible sources of emission could be the biomass burning and the second one could be the Secondary Organic aerosol (SOA) formation. Biomass combustion in the form of wood and coal in various area sources such as hotels, bakeries, crematoria and cooking fuel in lower income is one of the contributory sources of PM10 in the study area. In case of Mahul, dominant sources are industrial and thermal power plant emissions which emits large amount of PM10, SO2 and NOX along with the VOC.For better understanding the sources and precursors of SOA in terms of WSOC there is need for further characterization of water soluble compound for the group of compounds such as Mono and Di-carboxylic Acids, Humic Substances along with the EC, OC in PM10 and also in lesser fractions such as PM2.5 and PM1.0

Acknowledgment

The authors wish to thank National Institute of Industrial Engineering (NITIE) for providing instrumental facilities and thanks are due to NEERI staff at Mumbai Zonal Laboratory.

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References

1.Decesari, S., Facchini, M.C., Fuzzi, S., McFiggans, G.B., Coe H.and Bower and K.N., (2005). The Water- Soluble Organic Component of Size-Segregated Aerosol, Cloud Water and Wet Depositions from Jeju Island during ACE-Asia. Atmos.Environ. 39: 211-222.

2.Bao L., Sekiguchi K., Wang Q. and Sakamoto K.,( 2009).Comparison of Water-Soluble Organic Components in Size-Segregated Particles between a Roadside and a Suburban Site in Saitama, Japan

Aerosol and Air Quality Research, 9: 412-420, 2009

3.Kawamura, K. and Yasui, O. (2005). Diurnal Changes in the Distribution of Dicarboxylic Acids, Ketocarboxylic Acids and Dicarbonyls in the Urban Tokyo Atmosphere. Atmos. Environ.39: 1945-1960.

4.Hsieh, L.Y., Kuo, S.C., Chen, C.L and Tsai, Y.I. (2007). Origin of Low-Molecular-Weight Dicarboxylic Acids and Their Concentration and Size Distribution Variation in Suburban Aerosol. Atmos. Environ. 41: 6648-6661.

5.Karthikeyan S. and Balasubramanian R., (2005). Rapid Extraction of Water Soluble Organic Compound from Airborne Particulate Matter J.of Analytical Sciences, vol.21.

6.Graber, E. and Rudich, Y., (2006). Atmospheric HULIS: How humic-like are they? A comprehensive and critical review.Atmos. Chem. Phys., 6, 729–753.

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F–O–4

Black Carbon Aerosols over Mohal during Pre-monsoon and Monsoon Period in the Kullu Valley of the Northwestern Himalaya, India

Ajay K. Thakur and Jagdish C. Kuniyal*

G.B. Pant Institute of Himalayan Environment and Development, Himachal Unit,

Mohal-Kullu, (H.P.), India

*Corresponding author : E-mails: jckuniyal@rediffmail.com / jckuniyaljc@gmail.com

Introduction

Black Carbon (BC) emitted by incomplete combustion of carbonaceous fuel is a matter of great concern among scientific community due to its optically absorbing property. BC absorbs solar radiations in the visible and near infrared wavelengths where most of the solar radiations are distributed. BC has the ample potential to alter the Earth’s radiation budget (Haywood and Ramaswamy, 1998). BC data are essential for the prediction of change in radiative forcing that it causes. BC is an important constituent of ambient particulates matter. While BC remains inert in the atmosphere, it provides a surface that catalytically promotes certain reactions in the atmosphere, predominantly in presence of water. Absorbing aerosols heat the air, alter regional atmospheric stability, vertical motions and affect a large-scale circulation and hydrologic cycle with significant regional climatic effects (Menon et al., 2002). Enhanced atmospheric absorption due to high BC concentration has shown serious climatic effects (Ramanathan et al., 2001).

Observation Site and Instrumentation

The present observation site is at Mohal (31.9°N, 77.12°E, 1154 m amsl) which is situated in the Kullu valley of the Indian Himalayan region. It is a semi-urban location. The first time observation of BC at Mohal has been started since July, 2009. Earlier Kuniyal et al. (2009) studied Aerosol Optical Depth (AOD) for high altitude station at Mohal during ICARB in the year 2006. The present paper provides general status of BC and its relation with AOD during pre-monsoon and monsoon period (July 2009 to October 2009).

Regular and real time measurement of the mass concentration of the atmospheric BC was carried out using a seven beam Aethalometer (model AE-31, Magee scientific Inc., USA). The Aethalometer is fully automatic instrument that uses a continuous filtration of ambient aerosols and optical transmission measurement technique to estimate the mass concentration of BC. The Aethalometer was configured for air flow of 3 litre min-1 and measurement cycle (time base) was set to 5 min. This instrument this way provides BC mass concentration in ng m-3 in every 5 min.

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Results and Discussion

Based on hourly mean values for the four months, the peak concentration of BC was observed above 4000 ng m-3 between 0600 hr to 0900 hr IST while the other peak was observed above 3000 ng m-3 between 1800 hr to 2200 hr IST (Fig.1). Based on daily mean measurements, BC was maximum 6134±136 ng m-3 on September 26, 2009 and minimum 2741±16 ng m-3 on August 07, 2009 (Fig.2). It is also significant to reveal that BC concentrations simultaneously rise and fall with the values of Aerosol Optical Depth (AOD) monitored with the help of Multi-wavelength Radiometer (MWR).

2000

1000

Hours

Figure 1. Hourly mean values of BC at Mohal-Kullu in Himachal Pradesh.

During the observation period, MWR was operated for 18 full clear sky days. The segmented BC data corresponding to MWR data have shown the highest AOD with 0.51 and BC with 4201 ng m-3 on September 29, 2009. While the lowest AOD was 0.12 and BC

Days

Figure 2. Daily mean values of BC at Mohal-Kullu in Himachal Pradesh.

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2579 ng m-3 on October 10, 2009 (Fig. 3). The upward and downward trend of AOD with respect to BC shows significant thrust by BC on AOD. According to the observation for four months, mass concentration of BC was significantly high in the month of September 2009 (3680±20 ng m-3) and lowest in the month of August 2009 (2741±16 ng m-3). The main sources of BC in the present region were vehicular emissions and bio-mass burning.

Days

Figure 3. A comparative view of BC and AOD at Mohal-Kullu in Himachal Pradesh.

Acknowledgement

The authors are thankful to the Director, G.B. Pant Institute of Himalayan Environment and Development, Kosi-Katarmal, Almora, Uttarakhand for providing facilities in Himachal Unit of the Institute which could make the present study possible. The financial assistance to carry out the present work from ISRO, Bangalore is highly acknowledged.

References

Haywood, J.M. and Ramaswamy, V. (1998) Global sensitivity studies of the direct radiative forcing due to anthropogenic sulphate and black carbon aerosols, J. Geophys. Res., 103(D6): 6043–6058.

Kuniyal, J.C., Thakur, A., Thakur, H.K., Sharma, S., Pant, P., Rawat, P.S. and Moorthy, K.K., (2009) Aerosol optical depths at Mohal-Kullu in the northwestern Indian Himalayan high altitude station during ICARB, J. of Earth System Science 118(1): 41-48.

Menon, S., Hansen, J., Nazarenko, L. and Leo, Y. (2002) Climate effects of BC aerosols in China and India, Science, 297 (5590): 2250-2253.

Ramanathan, V., Crutzen, P. J., Lelieveld, J., Mitra, A. P., Althausen, D., Anderson, J. and Andreae, M. O. et al. (2001) Indian Ocean Experiment: An integrated analysis of the climate forcing and effects of the great Indo-Asian haze, J. Geophys. Res., 106(D22), 28: 371–398.

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F–O–5

Impact of Carbonaceous Aerosols over Indian Region

Hashmi Fatima, H. C. Updhyaya and O. P. Sharma

Centre for Atmospheric Sciences, Indian Institute of Technology Delhi,India

Asia is the region of the great source of global carbon emission and this trend is expected to increase in the near future. They are of two kind organic matter (OM) and black carbon (BC) aerosols. Black carbon stands after only carbon dioxide (CO2) in the list of climate change contributors. BC can directly absorb solar radiation or mix with other aerosols to form atmospheric brown clouds which absorb incoming solar radiation and prevent it from reaching the surface, warming the atmosphere. Thus, in this study, the Laboratoire de Meteorologie Dynamique model (LMD, version 3.3) is used to investigate the possible effect of carbonaceous aerosols over India for the monsoon periods on the atmospheric radiation transfer and over the precipitation. LMDZ.3.3 is integrated for different years for the Indian southwest monsoon periods over the globe for the resolution 96x72x19 (approx. 300 km). For analysing the radiative impact of carbonaceous aerosols, the experiment has been done for 2 years and the results presented here are the annual average of last year only. The simulation results show that BC aerosol induces a positive radiative forcing, while organic matter show negative radiative forcing at the top of the atmosphere and a negative radiative forcing at the surface in this region. However, the impact of BC and OM over rainfall is different and complex for different places. The sensitivity studies for carbonaceous aerosols have been done for 21 years (1987-2007) for the monsoon period, and the rainfall is compared with GPCP (Global Precipitation Climatology Project) with the help of Principal component analysis.

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Mean Monthly Rainfall Over India

Year

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References

1.Cookee, W. F., C. Liousse, H. Cachier, and J. Feichter, [1999], Construction of a 1x1 fossil fuel emission data set for carbonaceous aerosol and implementation and radiative impact in the ECHAM4 model, J. Geophys. Res., 104, 22137-22162.

2.Cookee, W. F., V. Ramaswamy, and P. Kashibhatla, [2002], A general circulation model study of the global carbonaceous aerosol distribution, J. Geophys. Res., 107, doi:10.1029/2001JD001274

3.Penner, J. E., R. E. Dickinson, and C. A. O’Neil [1992], Effects of aerosol from biomass burning on the global radiation budget, Science, 256, 1432-1433.

4.Reddy, M. S. And O. Boucher [2004], A study of the global cycle of carbonaceous aerosols in the LMDZT general circulation model, J. Geophys. Res., 109, D14202, doi:10.1029/2003JD004048

5.Menon, S., J. Hansen, L. Nazarenko, Y. Luo [2002], Climate effects of black carbon aerosols in china and India, Science, 297, 2250-2253

6.Ramanathen, V. [2007], Role of black carbon in global and regional climate change, Washington DC.

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F–O–6

Variations in CO, O3 and Black Carbon Aerosol Mass Concentrations Associated with Planetary Boundary Height (PBL) Dynamics: A Study over Tropical Urban Region of Hyderabad

K. V. S. Badarinath1*, D. V. Mahalakshmi, Anu Rani Sharma1, Shailesh Kumar Kharol1 and V. Krishna Prasad2

1Atmospheric Science Section, National Remote Sensing Centre,

Dept. of Space-Govt. of India, Balanagar, Hyderabad-500 625, India

2Department of Geography, University of Maryland, USA

* badrinath_kvs@nrsc.gov.in

Introduction

Rapid population growth together with industrialization and exponential growth in vehicular fleet are contributing to deteriorating air quality in several urban regions of India. Hyderabad (17o47’N and 78o50’ E) is the fifth largest city in India with a population according to 2001 census is 5,751,780. In particular, during the pre-monsoon season, due to frequent dust storms and dry spells of weather, the air masses carry dry dust particles from the western Thar Desert to the study region (Badarinath et al., 2007c). Also, the other pollutant sources include combustion processes and other non-combustion industrial processes. Most importantly, biomass burning from slash and burn agriculture crop practices, locally called “Jhum cultivation” are one of the major causes of increased pollutant levels during pre-monsoon season over the region. In the present study we have analyzed variation in CO, O3 and BC mass concentration during January-December, 2008 in the study area and influence of nighttime planetary boundary layer height and local meteorology on those variations.

Datasets and Methodology

The ground based measurements of CO, O3 and black carbon in addition to nocturnal planetary boundary layer (PBL) measurements from LIDAR were carried out in the premises of the National Remote Sensing Centre (NRSC) campus at Balanagar located within the Hyderabad urban center. DMSP-OLS night-time satellite data were analyzed to quantify forest fires over the region and their influence on the pollutant levels over urban region of Hyderabad. National Center for Environmental Prediction (NCEP) winds and local weather station data were analyzed to address the long range transport of pollutants over the region.

Results and Discussion

Figure–1 (a–d) shows the Julian day variation of daily averaged nighttime BC, O3, CO

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during winter (January–February) corresponded with low nighttime temperature. Also, boundary layer height increased during pre-monsoon period (March–May) and coincided with increase in nighttime temperature. In order to understand the increased loadings of BC and CO during night time, daily nighttime forest fire data derived from DMSP-OLS satellite over the Indian region was analyzed for January–May, 2008. Monthly composites of DMSP-OLS nighttime forest fire locations over Indian region during January-May, 2008 are shown in Figure - 2. Satellite data revealed fire intensity to be high during March- April, 2008. Also, fire counts were relatively higher in states like Andhra Pradesh, Chattisgarh, Orissa, Maharashtra and Madhya Pradesh, which are spatially closer to the measurement site.

Figure 2. DMSP-OLS derived nighttime forest fires over Indian region during January – May, 2008.

Conclusions

In the present study, variations of O3, CO and BC mass concentration were analyzed in relation to Planetary Boundary Layer height (PBL) and other meteorological conditions during January–December, 2008 in tropical urban area of Hyderabad, India. Results of the study suggested that –

zHigher values of BC and CO on certain Julian days during winter, pre-monsoon and post-monsoon season have been attributed to long-range transport of anthropogenic emissions due to forest fires and agriculture crop residue burning

practices over Indian region. The observed changes in nighttime O3 values are probably due to different amount and reactivity of O3 depletion components such as NO, VOC, secondary organic aerosol (SOA) in different environmental and meteorological conditions.

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Acknowledgements

The authors thank the Director of NRSC & Dy. Director (RS&GIS-AA), NRSC for necessary support and facilities.

References

Badarinath K. V. S., Kharol, S. K, Kaskaoutis D. G. and Kambezidis, H. D. 2007. Case study of dust storm over Hyderabad area, India: Its impact on solar radiation using satellite data and ground measurements. Science of the Total Environment, 384, 316–332.

Kharol, S. K. and Badarinath, K. V. S. 2006. Impact of biomass burning on aerosol properties over tropical urban region of Hyderabad, India. Geophysical Research Letters, 33, L20801, doi: 10.1029/2006GL026759.

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F–O–7

Vertical Profiles of Black Carbon Aerosols and BC Induced Heating Rates over Bangalore and Hyderabad

P. D. Safai, M. P. Raju, G. Pandithurai, A. Panicker, M. Konwar, P. S. P. Rao, P. C. S. Devara, R. Maheskumar and J. R. Kulkarni

Indian Institute of Tropical Meteorology, Pune-411 008

E-mail : pdsafai@tropmet.res.in

Introduction

Black carbon (BC) aerosols, the graphitic form of carbonaceous aerosol, is a primary aerosol emitted into the atmosphere as a by-product of all combustion processes. The large atmospheric absorption of solar radiation by BC and its consequent potential to alter the radiation budget of the earth’s atmosphere is well recognised. The global mean clear sky radiative forcing due to BC is estimated between +0.4 to +0.8 W m2 (IPCC, 2001). This large uncertainty arises from the uncertainties in the BC estimates. Being a combustion by-product, BC aerosols are generally in the fine and accumulation size range, and are hydrophobic or very weakly hydrophilic as they mix with other species. As such, they have long atmospheric life times and can be transported vertically to higher regions of the atmosphere, particularly in the tropics where the thermal convections are strong. Elevated BC layer over landmass with high reflectance or over scattering aerosol layer will enhance the atmospheric forcing and can even reverse the “white house effect” (Satheesh 2002). Radiative forcing due to BC crucially depends on the vertical profile of BC (Haywood and Ramaswamy 1998). Thus, the study of vertical distribution of BC has immense relevance in aerosol characterization and aerosol-cloud interaction. Studies on the effects of BC aerosols at surface have been reported earlier. However, the presence of BC aerosols is also observed and reported in upper troposphere and lower stratosphere (Pueschel et al., 1992; Blake and Kato 1995; Strawa et al 1999). The available information on vertical distribution of BC is limited even globally and especially over India except for a few recent efforts (Moorthy et al 2004; Tripathi et al 2005, 2007; Babu et al 2008).

Experimental Details

One of the major objectives of the CAIPEEX (Cloud Aerosol Interaction and Precipitation Enhancement Experiment) programme undertaken by IITM during June to September 2009 was to study and understand the interactions between aerosols and clouds that lead to the precipitation mechanism. Aircraft BC observations were carried out using an Aethalometer (Magee Sci. Inc., USA, AE-42) that was placed in an unpressurised part of the twin engine Piper Cheyenne N361 JC pressurized aircraft. Atmospheric air was pumped through an isokinetic inlet, at the flow rate of 6LPM and the time base for observations was set at 1 min interval. Details of the instrument and its operation have been discussed elsewhere (Hansen et al., 1984). In general, all the airborne measurements during CAIPEEX

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were carried out during the period 12.00 to 16.00 LT when the boundary layer was fully developed and strong convective motions might have set in by the time profiling was started.

Results and Discussions

Altitude distribution of BC aerosols

The altitude distribution of BC mass concentration (after the correction for temperature and pressure as reported by Moorthy et al., 2004) from the aircraft measurement made over Hyderabad (HYD) and Bangalore (BLR) is shown in Fig. 1. The profiling was done over the region at different levels to get a good height resolution. At each level, the aircraft flew steadily for about 5 min, and the data obtained during this period were averaged to obtain the mean value representing that altitude. The altitude distribution of BC mass concentration over Hyderabad on 11 June 2009 depicts that at the surface level, average BC mass concentration was ~1720 ± 845 ng/ m3. Then, there was a sharp decrease in BC concentration from surface to about 0.5 km and then a gradual vertical decrease with in between peaks at 1 km (815.4 ng /m3), 2.5 km (825.5 ng/ m3), 4 km (388 ng /m3) and 5.5 km (525.4 ng /m3). The lowest concentration (221.6 ng/m3) was observed at about 6 km height. Similarly for Bangalore on 3 June 2009, the vertical distribution of BC mass concentration showed gradual decrease with height from surface to about 7 km. The average surface BC concentration was 1245 ± 652 ng /m3 which decreased to 207.4 ng /m3 at 6.8 km. However, there was a significant peak at 4 km (711.6 ± 965 ng /m3) and small peaks at 5 km (450.5 ng /m3) and 6.5 km (258.6 ng /m3). Thus, the BC mass concentrations observed at the heights of about 7 km at HYD & BLR are low compared to those observed at the surface. However, the presence of about 200 ng /m3 BC at those heights as well as its peak concentrations observed at different heights can have important implications to the radiative forcing.

Figure 1. Vertical profiles of BC mass concentration at Bangalore and Hyderabad during CAIPEEX-2009

Air mass Trajectory Analyses

Vertical advection from surface sources and/or transport from other potential sources could be the reasons for the presence of BC aerosols at higher altitudes. To assess the role of long range transport, 7-day air mass back trajectories using NOAA Hysplit model

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(Draxler and Rolph, 2003) were computed for the different heights at which the peaks in BC concentrations were observed for HYD & BLR (Fig. 2) It was observed that at HYD on 11 June 2009, at 1 km and 2.5 km, the air masses were arriving far away from West Asian region (550 E) and at 5.5 km, they were from nearby Central Indian region. Similarly at BLR, air masses at 4 km were from Central India then through SE Indian region and finally over Arabian Sea before reaching the study area. Whereas, at 5 km they were from Eastern coast of South Africa and crossing across Arabian Sea and at 6.5 km, they were from west Asian and Gulf region, again crossing over the Arabian Sea before reaching the area under observation. This shows possible contribution of BC aerosols through advection from West Asian/ East African regions as well as that from the Central and Eastern Indian regions to the observational sites; apart from the local anthropogenic activities at the surface.

Figure 2. Air mass back trajectories at Bangalore and Hyderabad during CAIPEEX-2009

BC Induced Radiative Forcing and Vertical Heating Rates

BC induced surface radiative forcing and heating rates were estimated over Hyderabad (Fig. 3). Observed BC concentrations were converted in to BC number density as explained by Hess et al. (1998). The derived BC number density at the surface was used in the Optical Properties of aerosols and Clouds (OPAC) model (Hess et al. 1998) to derive BC aerosol optical properties such as aerosol optical depth (AOD), Single Scattering albedo (SSA), and Asymmetry parameter (ASP). These parameters were incorporated in Santa Barbara Discrete ordinate Radiative Transfer model (SBDART) (Richiazzi et al., 1998) to derive short wave fluxes (0.3- 3 μm) at the surface. Also aircraft measured vertical profiles of BC, temperature and relative humidity up to 7 km were used in the model. In addition, MODIS derived columnar water vapour and OMI derived column ozone values were also used in SBDART. The fluxes were derived for no BC aerosol condition also and the

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forcing over Hyderabad was -19.5 and 9.5 Wm-2

over surface and TOA respectively. BC induced Atmospheric heating rates were found to follow the same pattern as that of the vertical BC profile for that period. The heating rates were 0.77, 0.53, 0.64 and 0.58 K/day respectively at surface, 1 km, 2.5 km and 5.5 km. Tripathi et al (2007) have reported vertical profiles of heating rates at Kanpur up to 1.5 km during summer season (June) of 2005. They have reported that the heating rate profile during forenoon showed highest value (2.1 K/day) at 300 m whereas that during afternoon showed highest value at 1200 m (1.82 K/day).

References

Intergovernmental Panel on Climate Change (IPCC), 2001. In: Houghton, J.T., et al. (Eds.), Climate Change 2001: The Scientific basis: Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, New York, 881pp.

Satheesh, S. K., 2002. Aerosol radiative forcing over land: effect of surface and cloud reflection; Ann. Geophys. 20 1–5.

Haywood, J.M. and Ramaswamy, V., 1998. Global sensitivity studies of the direct forcing due to anthropogenic sulfate and black carbon aerosols. Journal of Geophysical Research 103, 6043–6058.

Pueschel, R F., Blake, D. F., Snetsinge, K . G. Hansen, A.D.A., Verma, S. and Kato, K., 1992. Black carbon (soot) aerosol in the lower stratosphere and upper troposphere; Geophys. Res.Lett. 19(16), 1659–1662.

Strawa, A W., et al., 1999. Carbonaceous aerosol (soot) measured in the lower stratosphere during POLARIS and its role in stratospheric photochemistry; J. Geophys. Res.104(D21) 26,753– 26,766.

Blake, D. F. and Kato, K., 1995. Latitudinal distribution of black carbon soot in the upper troposphere and lower stratosphere; J. Geophys. Res. 100 7195–7202.

Moorthy, K.K., Suresh Babu, S., Sunilkumar, S.V., Gupta, P.K. and Gera, B.S., 2004. Altitude profile of aerosol BC, derived from aircraft measurements over an inland urban location in India. Geophysical Research Letters 31, 22103.

Tripathi, S.N., Dey, S., Satheesh, S.K., Lal, S. and Venkataramani, S., 2005. Enhanced layer of black carbon in a north Indian industrial Indian city, Geophysical Research Letters 32, L12802.

Tripathi, S.N., Atul K. Srivastava, Sagnik Dey, S.K. Satheesh and K. Krishnamoorthy, 2007. The vertical profile of atmospheric heating rate of black carbon aerosols at Kanpur in northern India,

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Atmospheric Environment 41, 6909–6915.

Babu, S.S.,S K Satheesh, K Krishna Moorthy, C B S Dutt,Vijayakumar S Nair, Denny P Alappattu and P K Kunhikrishnan, 2008. Aircraft measurements of aerosol black carbon from a coastal location in the north-east part of peninsular India during ICARB.

J. Earth Syst. Sci. 117, S1, 263–271.

Hansen, A.D.A., Rosen, H. and Novakov, T., 1984. The aethalometer: An instrument for the real time measurements of optical absorption by aerosol particles. Science of Total Environment, 36, 191-196.

Draxler, R.R. and Rolph, G.D., 2003. HYSPLIT (Hybrid Single-Particle Lagrangian Integrated Trajectory) Model , NOAA Air Resources Laboratory, Silver Spring, MD. NOAA ARL READY (Website http:// www.arl.noaa.gov/ready/hysplit4.html).

Hess, M., P. Koepke, and I. Schult, 1998. Optical properties of aerosols and clouds: The software package OPAC, Bull. Amer. Meteorol. Soc., 79, 831-844.

Ricchiazzi, P., S. Yang, C. Gautier and D. Sowle, 1998. SBDART: A research and teaching software tool for plane parallel radiative transfer in the Earth’s atmosphere, Bull. Amer. Meteorol. Soc., 79, 2101-2114.

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F–O–8

Seasonal and Diurnal Variations of Black Carbon Aerosols over Tropical Urban Site Hyderabad India

U. C. Dumka, P. R. Sinha, R. K. Manchanda and S. Sreenivasan

Tata Institute of Fundamental Research, National Balloon Facility, Hyderabad 500 062, India

E-mail: ucdumka@gmail.com

Introduction

The aerosol black carbon (BC) or soot is a byproduct of all incomplete combustion processes (fossil fuel and biomass) and as such most of the atmospheric BC is of anthropogenic origin and is generally in the fine (< 2 μm) size range. It has a long atmospheric life time (days to weeks) making it amenable for easy transport both horizontally and vertically to higher regions of the atmosphere. Because of its strong absorption over a wide range of wavelengths, BC contributes significantly to atmospheric warming and its forcing potential strongly depends on the vertical profiles. The study of BC aerosol is become very important because of its strong absorbing potential and contribution to the greenhouse warming. Though, it contributes only a few percent to the total aerosol mass, its radiative effects are significant [Jacobson, 2001; Babu et al., 2004]. In the present study, the extensive measurements of the mass concentration of BC were carried out, during the period December 2008 to November 2009 over the tropical urban site Hyderabad.

Experimental Details and Data Base

With its ~ 5.5 million inhabitants, the study area Hyderabad (17.5o N, 78.6o E, 551 m above the mean sea level) is the fifth largest city in India and is also considered as one of the most polluted [Beggum et al., 2009], which is due to the direct results of the growth in population and associated activities that have been observed during the last decades. The measurements have been carried out in the premises of National Balloon Facility (NBF); Tata Institute of Fundamental Research (TIFR) Hyderabad located ~ 3 km away from the main city. Regular and near-real-time measurements of the mass concentration (MB) of BC were carried out, using an Aethalometer (model AE42 of Magee Scientific). The Aethalometer has been operated at a time base of 5 minutes, round the clock, at a flow rate of 5 liter per minute. More details regarding the instrument, principle of observations and data analysis are given elsewhere [Babu et al., 2004; Dumka et al., 2009].

Results and Discussion

Figure 1 shows the monthly/seasonal variation of black carbon mass concentration aerosols mass concentration over the study area. The daily mean BC mass concentration varied from about 1 to 16 μg m-3. However, monthly variation of BC mass concentration shows decreasing trend from December to July and then its start increasing and attains a peak value during December.

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A large value of BC mass concentration is also reported by Beegum et al [2009] for Hyderabad. The BC value were highest during winter (December to February), ~8.22 ± 0.25 μg m-3, and lowest during summer (June to August), ~ 2.77 ± 0.09 μg m-3 shows large seasonal variations (See Figure 1(a)). In addition to large seasonal variation in BC mass concentration also exhibits strong well defined diurnal variations (See Figure 1(b)), with a morning peak and minimum at afternoon.

The diurnal variations are characterized by nocturnal peak, early morning decrease, followed by a fumigation peak and steady decrease as the day advance to reach the lowest values in the afternoon, when the convection is deepest, peaks with lower levels during daytime. The diurnal variations of BC mass concentration are prominent during winter months. This diurnal variation is seasonal dependent and closely associated with the variation of local atmospheric boundary layer evolutions.

Figure 1. (a) The geographical location of the study area over the Indian subcontinent. Color code in the figure shows the altitudes in meters above the mean sea level. (b) The monthly mean diurnal variation of black carbon aerosol during January to December 2005 and 2006

Conclusions

The main conclusions of our studies are as follows:

1.The monthly/seasonal variation of BC mass concentration showed high concentration during the dry winter (December to January) and low concentration during summer (June to August) seasons.

2.The monthly mean BC mass concentration shows well defined diurnal variations with a morning peak and minimum at afternoon. This diurnal variation is closely associated with the variation of local atmospheric boundary layer evolutions.

Acknowledgements

This work was carried out as a part of Indian Space Research Organization, Geosphere Biosphere Program (ISRO-GBP).

References

Babu et al., Geophys. Res. Lett, Vol 31, L06104, doi: 10.1029/2003GL018716, 2004.

Beegum et al., Atmos. Envi., 43, 1071-1078, 2009.

Dumka et al., Atmos. Res., Accepted. 2009.

Jacobson, Nature, 409, 695-697, 2001.

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F–P–1

Atmospheric Black Carbon Removal with Efficient Rainfall Scavenging over Darjeeling during SW Monsoon

A. Chatterjee*, A. Adak, S. K. Ghosh, S. Raha, A. K. Singh and Y. Yadav

Bose Institute, Kolkata

* Presently at National Atmospheric Research Laboratory, Gadanki, India – 517 112

Introduction

Atmospheric black carbon (BC) particles are one of the crucial factors in the global climate change phenomena. Black carbon is emitted into the atmosphere as a by- product of all combustion processes and enriched mainly as sub-micron aerosol particles. These aerosol particles are removed from the atmosphere through the wet deposition process by irreversible captured by the hydrometeors being an exponential decay process (Pandey et al., 2002).

A plenty of studies were done on the scavenging of several aerosol components on a global scale but a few studies are there on the scavenging of black carbon by rainfall. This study is thus an attempt to estimate the wet scavenging coefficient of black carbon in a high altitude observation site, Darjeeling at the north-eastern Himalayas.

Methodology

The data of black carbon concentrations were collected using an Aethelometer (Model AE-21, Magee scientific, USA) during Jan-Dec’2008. The measurements were based on the attenuation of light through the quartz filter tape onto which the aerosol particles are made to impinge. The attenuation is proportional to the surface concentration of black carbon. The rain samples were collected using a 21 cm funnel fitted onto 2 lit capacity polythene bottle and rainfall intensity was calculated by the volume

of rain, surface area of the collector and the duration of the rain. The rainfall information were also obtained from the Indian Meteorological Department.

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It was observed that, the BC concentration decreased gradually with the increase in rainfall rate. The variation in

BC concentrations with the rainfall rate during the entire study period is shown in Fig 2 showing the inverse relationship.

The wet scavenging coefficient of black carbon (sec-1), the function of particle size and rainfall intensity, was determined using the following relation (Latha et al 2005):

Where Ws(BC) is the wet scavenging coefficient of black carbon, P is the rainfall rate and “a” and “b” are the parameters obtained from the regression relation between BC and rainfall intensity. Thus the average wet scavenging coefficient for black carbon in Darjeeling during the entire study period was estimated to be 2.25 10-4 sec-1 showing a significant scavenging.

References

Latha K. M, K. V. S. Badarinath, P. M Reddy (2005), Scavenging efficiency of rainfall on black carbon aerosols over an urban environment Atmos. Sci. Let., 6, 148–151

Pandey J S, Khan S, Joseph V, Kumar K (2002), Aerosol scavenging: model application and sensitivity analysis in the Indian context. Environ. Monito and Assess, 74: 105–116.

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F–P–2

Properties of near Surface Black Carbon Aerosols in a Rural Tropical Location

Gayatry Kalita, Binita Pathak, P.K. Bhuyan and K. Bhuyan

Centre for Atmospheric Studies,Dibrugarh University, Dibrugarh 786004, India

Introduction

Atmospheric Black carbon resulting from incomplete combustion of fossil fuels, biomass burning etc plays a major role in the dimming of the surface and in the atmospheric heating process. BC absorbs the solar radiation reflected by the earth’s surface and clouds, which would have otherwise escaped to space and thereby warms the atmosphere. By changing the latent and sensible heat fluxes due to land-use modifications, atmospheric Black Carbon can change the vertical distribution of heating in the atmosphere and hence relates the TOA radiative forcing directly to the surface temperature (Ramanathan, 2007). Black carbon in soot particles is potentially the second major contributor to the observed twentieth century global warming. Regular monitoring of BC aerosols across various parts of India is imperative to assess their radiative impacts on regional as well as global scale.

In the present study, near surface atmospheric black carbon properties are reported for a rural tropical site Dibrugarh (27.27°N, 94.54° E, 82 m amsl), in the North- eastern part of India for the period October, 2008 to September, 2009.

Methodology

A seven channel Aethalometer (Magee Scientific; Model AE31-ER) is used to estimate the near surface BC mass concentration from the attenuation of light transmitted at seven wavelengths viz. 370, 470, 520,590, 660, 880 and 950nm. The spectral absorption of BC from fossil fuel sources peaks at 830 nm wavelengths and hence the 880 nm channel is considered as the standard channel for BC measurement. From the raw radiance data recorded by Aethalometer, aerosol absorption coefficient values at seven wavelengths are derived by using the formula

Where I1 and I2 are the ratios of the intensities recorded by the detector for sensing beam to the references beam before and after each sampling interval of time t. Q is the volume of air sampled through the filter during interval t and A is the area of the spot where aerosols are collected. C ( ) is the wavelength dependent value obtained from the work of Bodhaine (1995) and R is an instrumental empirical correction factor which is taken as unity. The Angstrom absorption co-efficient a is a measure of spectral dependence aerosol absorption which is determined by using a power law relationship: ,

where is the BC spectral absorption co-efficient, is wavelength of the channels.

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Results

BC mass concentration exhibits almost identical day-to-day variability as seen from the seasonally averaged hourly plots [Figure 1]. BC mass concentration shows a primary peak around 2000-2200 hrs and a less prominent secondary maximum in the morning hours between 0600-0800 hrs. Highest value of BC mass concentration of about 40μg m-3 is observed in winter. The diurnal peak slightly shifts with season. Minimum BC was observed in the daytime between 1000-1600 hrs. Identical diurnal variation in all seasons suggests that diurnal variation of BC is mainly governed by the diurnal evolution of atmospheric boundary layer (ABL), which remain low during morning hours, then gradually increases and reaches a high value in noon time and starts decreasing in the evening [Krishnan and Kunhikrishan, 2004]. Later in the evening and throughout the night, on the other hand, the radiative cooling of the ground surface results in the suppression or weakening of turbulent mixing and consequently in the shrinking of the ABL depth. This results in the confinement of aerosols and a consequent increase in its concentration during early night period. After reaching a peak level, BC concentration decreases gradually due to reduction in anthropogenic activities. Seasonal variations in BC mass concentration mainly occurs because of differences in the extent of contraction and expansion of the atmospheric boundary layer as a result of differential solar heating of the earth’s surface as well as differences in sources and strengths of production in different seasons. Gradual increase in BC concentrations from around 1600 hrs is due to increased production of BC aerosols and gradual formation of a surface based inversion opposing vertical mixing in the atmosphere. Another reason of evening time increase in BC is open burning of solid wastes such as dry leaves and other garbage materials, particularly during dry and post- monsoon seasons. In addition to waste burning, wood and shrubs are also burnt at night by several people to keep themselves warm during cold winter months. Due to the same reason a small secondary peak in winter is observed at around 0700 hrs. Removal of particles from the atmosphere by gravitational settling process results in minimum BC concentration during early morning hours.

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The measurement of spectral dependence

of absorption (a) is determined by linear regression ln ( )abs and ln ( ). The values of a are found to be 0.404, 0.363, 0.372 and 0.367 for retreating monsoon, winter, premonsoon

and monsoon respectively exhibiting weak wavelength dependence of black carbon aerosols. This also indicates that black carbon aerosols are not the dominant component in the total fine mode aerosol over this location.

References

Babu, S. S., and K. K. Moorthy (2002), Aerosol black carbon over a tropical coastal station in India, Geophys. Res. Lett., 29 (23), 2098, doi: 10.1029/2002GL015662.

Bodhaine, B.A. (1995), Aerosol absorption measurements at Barrow, Mauna Loa and the South Pole, J. Geophys. Res., 100, 8967-8975.

Krishan, P. and P. K. Kunhikrishan (2004), Temporal variations of ventilation coefficient at a tropical Indian station using UHF wind profiler, Curr. Sci., 86(3), 447-451.

Ramanathan, V. (2007), Role of Black Carbon in Regional Climate Changes, a report presented to the House Committee on Oversight and Government Reform Chair :The Honourable Henry A Waxman.

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Black Carbon Aerosol Mass Concentrations Observed over Anantapur, a Tropical Semi-arid Station in Southern India

K. Raghavendra Kumar*, G. Balakrishnaiah, B. Suresh Kumar Reddy, K. Rama Gopal, R.R.Reddy and K. Narasimhulu

Aerosol and Atmospheric Research Laboratory,Department of Physics,

Sri Krishnadevaraya University,Anantapur-515055, India.

*Email: kanike.kumar@gmail.com

Introduction

The aerosol Black Carbon (BC) is a byproduct of all incomplete combustion processes (fossil fuel and biomass) and as such most of the atmospheric BC is of anthropogenic origin. BC is the optically absorbing part of carbonaceous aerosols, primarily emitted from combustion (Beegum et al., 2009). It is a major anthropogenic component of atmospheric aerosols, which has significantly different optical and radiative properties as compared to the other normal constituents. BC acts as an indicator of airmass affected by anthropogenic pollution. Absorption by BC lowers the aerosol single scattering albedo (SSA), increasing the amount of radiation absorbed in the atmosphere (Haywood and Shine, 1997).

Being present mostly in the sub-micron size range, it is easily inhaled and can be a health hazard (Horvath, 1993). Recently, BC has also been used as an indicator of exposure to diesel soot (Fruin et al., 2004). The two most important sources for atmospheric BC are fossil fuel combustion (for example automobile exhaust, industrial and power plant exhausts, aircraft emissions, etc) and biomass burning (burning of agricultural wastes, forest fires). While biomass burning may be the dominant BC source over tropical regions and most of the southern hemisphere, the role of fossil fuel combustion is usually more important in cities, especially over the northern hemisphere. Due to its environmental and climatic significances, as well as anthropogenic nature of its origin, characterization of BC has attracted considerable interest in the recent years (Hansen et al., 1984).

Instrumentation, Methodology and Uncertainties

Black Carbon aerosol mass concentration measurements began in Anantapur from August 2006 using a dual wavelength Aethalometer (AE-21 of Magee Scientific, USA). AE-21 measures BC mass concentrations at two wavelengths 370 and 880 nm. The measurements are made from terrace of the building at an altitude of about 15 m above the ground using its inlet tube and pump. The BC mass concentrations ([BC]) are estimated using the optical method of measurement of the attenuation of a beam of light transmitted through the sample collected on a filter, which is proportional to the amount of BC mass loading in the filter deposit (Hansen et al., 1982, 1984). This is a filter based technique that measures the light attenuation due to particles deposited onto a filter. The yielded attenuation absorption coefficient is then converted into BC mass concentration. The conversion of attenuation absorption coefficient into BC mass concentration is done using

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appropriate absorption efficiency values. The absorption efficiency varies as a function of wavelength.

The limitations and uncertainties of aethalometer in BC measurements and corrections needed are well documented in the recent literature (Weingartner et al., 2003;). The effective specific absorption cross-section accounts for the amplification of the absorption due to multiple scattering in the filter fiber matrix (the so called ‘C’ factor, Weingartner et al., 2003) and also the ‘shadowing’ effect (‘R’ factor) to certain extent (Beegum et al., 2009). Taking into account all these effects, the overall uncertainty in the reported BC mass concentrations is estimated to be about a maximum of 10%.

Aethalometer was operated at the flow rate of 3 l min-1, for 24 hours a day at a time resolution of 5 min. The BC measured at 880 nm wavelength is considered to represent a true measure of BC in the atmosphere as at this wavelength BC is the principal absorber of light while the other aerosol components have negligible absorption at this wavelength. The measurement location is a semi-arid region and is dominant by local sources, mainly anthropogenic. As at 880 nm the major absorbing species is BC, in this work, BC mass concentrations measured at 880 nm from August 2006 to October 2009 in Sri Krishnadevaraya University (SKU), Anantapur are analyzed and reported.

Monthly and seasonal variations in BC mass concentrations

BC aerosol mass concentrations measured for 24 hours a day in a particular month are averaged and the monthly mean BC mass concentrations are obtained. In Figure 1 the monthly mean BC aerosol mass concentrations measured over Anantapur from August

Figure 1. Monthly mean black carbon aerosol mass concentrations at Anantapur during the period August 2006 – October 2009. The vertical lines passing through the points represent ± 1s deviations and the horizontal line shows average background values of BC

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2006 to October 2009 are plotted. Vertical bars indicate ±1s deviation from the mean value of measured BC mass concentrations and indicate the variability in the BC mass measured during that particular month. The horizontal line parallel to abscissa represents the mean BC mass concentration for entire study period. The annual average BC mass concentration at Anantapur during August 2006-October 2009 was 2.47±0.22 μg m-3. Seasonal variations suggest large concentrations of BC (~3.84±0.59 μg m-3) during winter (December, January, February), followed by those in the post-monsoon (October and November) and summer (March, April and May) and low BC concentrations (<~1.21±0.35 μg m-3) during the monsoon months (June, July, August, September). In fact, average BC concentrations in winter (3.81±0.61 μg m-3), postmonsoon (2.84±0.51 μg m-3) and summer (2.55±0.35 μg m-3) was double than that in monsoon (1.24±0.47 μg m-3).

The average BC concentrations were about 60% higher in winter than in summer and postmonsoon (about 40%). As the measurement location is not highly industrialized and the seasonal and diurnal variations in BC mass concentrations can mainly be attributed to the synoptic meteorology, biomass burning and transport from the surrounding regions, while the contribution from vehicular emissions could be minimal throughout the year. During dry months (December – May) large BC concentrations are associated with large diurnal oscillations in ambient temperature and scanty rainfall. Low BC concentrations occur during the monsoon months (June – November) when the station experiences high rainfall, low temperature and the indicative of the effect of washout of aerosols. This is mainly due to high convective activity and also responsible for the dispersal of aerosols (especially those in fine size).

High BC values during summer months of March and April has been attributed to the transport of airmass from continental regions in addition to the increase in fossil fuel consumption (diesel and petrol) for road transportation. During the monsoon period, the atmosphere is generally wet with periodic cleansing of the atmosphere and hence the mean BC concentrations are low and the boundary layer dynamics are minimum during this season resulting in insignificant diurnal variation.

Diurnal and temporal variations in BC mass concentrations

The average diurnal variations in BC aerosol mass concentrations measured over Anantapur during August 2006 – October 2009 are plotted for different seasons. The monthly mean concentrations as a function of time are plotted in Fig. 2. The monthly average sunrise and sunset times corresponding to seasons over Anantapur are plotted as vertical arrow marks in the figure. At the outset, the BC mass concentrations are found to show distinctly different diurnal variations in the four seasons. The diurnal mean BC mass concentration was around 4.89±0.24 μg m-3 in winter, 3.32±0.22 μg m-3 in summer, 3.53±0.12 μg m-3 in post monsoon and 1.24±0.11 μg m-3 during the monsoon season. The prominence of this type of diurnal variation as well the magnitude of BC mass concentration decreases during the summer months with morning peak value of 4.93±0.29 μg m-3, noon value of 2.43±0.13 μg m-3 and nocturnal peak value of 3.23±0.24 μg m-3.

The BC mass concentrations are constant from midnight to 0600 hours. The building up of BC mass concentrations starts after 0600 hours. The peak BC concentrations in the morning hours occur at around 0700 hours and then the values decrease. The BC mass concentrations are constant and at background levels from 1000 to 1700 hours when there is much less vehicular movement in the location. As Anantapur is a suburban, semi-

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arid location surrounded by a number of stone crushing industries, brick making units etc., the diurnal and seasonal variations in BC mass concentrations can mainly be attributed to the vehicular emissions and transport from the surrounding regions, while the contribution from biomass consumption could be minimal throughout the year. The BC mass concentrations are found to be less in the afternoon hours when there is much less anthropogenic sources of BC. The peak BC concentrations are found in the evening hours at around 2100 hours after which the BC concentrations decrease. Similar features in diurnal variations in BC mass concentrations have observed at a coastal station in Trivandrum (Babu and Moorthy, 2002). The absolute BC mass concentrations are higher in winter due to the shallow boundary layer which results in trapping of pollutants. The local sources in arid location, mainly vehicular traffic, contributes to the diurnal peaks in BC concentration and the effect gets enhanced during winter due to boundary layer dynamics.

Aerosol concentration is affected by the stability of boundary layer, which is active during the daytime due to surface temperature increase and stable at night (Stull, 1988). It has been shown that the nocturnal boundary layer is shallower than its daytime counterpart by a factor of about 3 (Kunikrishnan et al., 1993). Also, as the wind speeds, in general, are lower during night the ventilation coefficient rapidly reduces, resulting in the confinement

Figure 2. Average diurnal variations of BC mass concentrations for different seasons during August 2006 – October 2009 with ±1s deviations for the mean. The vertical arrow marks on the abscissa represents the local sunrise (SR) and sunset (SS). The fumigation peak shows more dominant than the nocturnal peak in all seasons except in the monsoon season.

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of aerosols during nighttime. This results in an increase in the BC mass concentration during early nighttime (Babu and Moorthy, 2002). The BC mass concentration reduces as the night advances due to reduction in anthropogenic activities and loss in particles closer to the surface by sedimentation. The gradual buildup of the BC mass concentration from the morning hours and the occurrence of peak between 0700 and 0900 hours about an hour after the sunrise during both winter and summer are attributed to the combined effects of fumigation effect of the boundary layer and morning increase in the anthropogenic activities in a semi-arid environment. The fumigation effect in the boundary layer brings in aerosols from the nocturnal residual boundary layer in a short time after the sunrise (Stull, 1988). The increased solar heating as the day advances produces a deeper and more turbulent boundary layer which leads to a faster dispersion resulting in a dilution of BC near the surface (Babu and Moorthy, 2002). The surface aerosol loading in arid areas typically found to be the smallest from late night to early morning (0300-0600 hours local time) and increases to the first maximum in a day at around 1000 hours which drops in the afternoon until the occurrence of the second peak around 2000 hours. The peaks were attributed to the early morning and late afternoon vehicle combustion resulting from the rush hour traffic.

BC mass concentration as function of local wind patterns

The monthly mean wind speeds over Anantapur are plotted as a function of BC concentrations from August 2006 to October 2009 is shown in Fig. 3. The horizontal line in the figure shows the average value of BC concentrations from the normal background measurements over the study area which is found to be ~2484 ng m-3 (shown in Fig. 1). The monthly average BC concentrations found to be ~5 times higher during January (~5390 ng m-3) than July (~865 ng m-3). This increase in BC concentrations during the winter period has been attributed to the emissions transported from northeasterly direction by the action of favorable winds which is in well agreement with the sources originating from northern Indo-Gangetic Plain derived from HYSPLIT (figure not shown). Black carbon aerosol levels came down to back ground levels in the subsequent months immediately.

An attempt has been made to investigate the possible relation of BC to the meteorological parameters although there is a clear “source” effect on BC mass concentrations in the observational site. Although there is a tendency of high BC concentrations associated with high wind speed, this association may be coincidental (as during daytime, both higher wind speed and more traffic density may occur), and moreover, high BC concentrations are not visible during all occurrences of high wind speeds. The monthly mean wind speeds are low and are in the range of 1-2 ms-1 during October-March which increases to about 4 ms-1 during May-July. It is probable that due to higher wind speeds, BC produced from local sources are transported to other locations (Ramachandran and Rajesh, 2007). Hence the large decrease in the BC concentrations from February to March and during August can be very well attributed to the prevailing high wind speeds. Even though very high BC concentrations occurred during the winter months, on several occasions, very low concentrations (<500 ng m-3) were also observed. These can be attributed to the increase in the wind speeds associated with the mistral phenomenon, which was frequently encountered during the study period. Hence, even though there is continuous BC emission in the atmosphere, the high wind speeds associated with the mistral phenomenon effectively disperse the aerosols, thereby causing a decrease in the BC concentration.

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Similarly high shifts of mean wind speed values did not produce significant comparable shifts in BC concentrations. Increased wind speed leads to faster dispersion and hence a dilution of BC nears the surface and vice-versa. Similar observations have been made in other studies in literature (Bhugwant et al., 2000). It was argued that a clear correlation between wind speeds and BC mass concentrations gives an indication of the proximity of BC sources at the measurement site, while a not so significant correlation shows that the BC originates from distant sources. The high BC concentrations during winter can also be correlated with the wind direction. It is observed that during winter season, wind patterns start shifting in direction from northeasterly to southwesterly where possible sources of BC are generated from northern IGP and central India and are concentrated near the measurement site (not transported to the other locations) due to low wind speeds (~1.2 ms-1).

Figure 3. Annual variations of BC mass concentration in dependence of local wind speeds for individual months during August 2006 – October 2009 are averaged

Acknowledgements

This work has been carried out with the financial assistance DST, New Delhi and ISRO-GBP, Bangalore.

References

Babu, S. S., and Moorthy, K. K., 2002. Aerosol black carbon over a tropical coastal station in India. Geophys. Res. Lett., 29(23), 2098, doi: 10.1029/2002GL015662.

Beegum, S.N., Moorthy, K.K., Babu, S.S., Satheesh, S.K., Vinoj, V., Badarinath, K.V.S., Safai, P.D., Devara, P.C.S., Singh, S.N., Vinod, Dumka, U.C. and Pant, P., 2009. Spatial distribution of aerosol black carbon over India during pre-monsoon season. Atmos. Environ. 43, 1071-1078.

Bhugwant, C., Cachier, H., Bessafi, M. and Leveau, J., 2000. Impact of traffic on black carbon aerosol concentration at La Reunion Island (Southern Indian Ocean). Atmos. Environ. 34, 3463-3473.

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Fruin, S. A., Winer, A. M. and Rodes, C. E., 2004. Black carbon concentrations in California vehicles and estimation of invehicle diesel exhaust particulate matter exposures. Atmospheric Environment 38, 4123- 4133.

Hansen, A. D. A., Rosen, H. and Novakov, T., 1982. Real-time measurements of the absorption coefficient of aerosol particles. Applied Optics 21, 3060-3062.

Hansen. A. D. A., Rosen, H. and Novakov, T., 1984. The aethalometer; An instrument for the real-time measurements of optical absorption by aerosol particles. Sci. Total Environ., 36, 191-196.

Haywood, J. M. and Shine, K. P., 1997. Multi-spectral calculations of the radiative forcing of tropospheric sulphate and sort aerosols using a column mode. Q. J. R. Meteorol. Soc., 123, 1907-1930.

Horvath, H., 1997. Experimental calibration for aerosol light absorption measurements using the integrating plate method-summary of the data. Journal of Aerosol Science 28, 1149-1161.

Kunhikrishnan, P.K., Sen Gupta, K., Radhika, R., Prakash, J.W.J., Nair and K. Narayanan, 1993. Study on thermal internal boundary layer structure over Thumba, India. Ann. Geophys. 11, 52–60.

Ramachandran, S., Rajesh, T. A., 2007. Black carbon aerosol mass concentration over Ahmedabad, an urban location in western India: Comparison with urban sites in Asia, Europe, Canada, and the United States. Journal of Geophysical Research 112, D06211, doi:10.1029/2006JD007488.

Stull, 1998. An Introduction to Boundary Layer Meteorology. Kluwer Academic Publishers, Dordrecht.

Wiengartner, E., Saathoff, H., Schnaiter, M., Streit, N., Bitnar, B., and Baltensperger, U., (2003). Absorption of light by soot particles: Determination of the absorption coefficient by means of aethalometers. J. Aerosol Sci., 34, 1445-1463.

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Summertime Characteristics of Black Carbon Aerosols At a High Altitude Station in South West India

M.P.Raju, P.D.Safai, K.B. Budhavant, P.S.P.Rao and P.C.S. Devara

Indian Institute of Tropical Meteorology, Pune – 411 008, India

Introduction

Aerosol Black Carbon (BC), the highly absorbing carbonaceous aerosols, has been the major anthropogenic component of atmospheric aerosol system. The importance of BC in climate change studies have been ascertained by different studies (Ramanathan et al., 2001).Burning of biomass and fossil fuels, automobile exhaust, aircraft emissions and forest fires are the chief sources of Black Carbon (BC) aerosols. Studies on BC aerosols have been scarce from the Indian region, especially from the high altitude locations. Ground-based observations on aerosol particles (PM1.0, PM2.5 and PM10), Black Carbon (BC) aerosols, Aerosol Optical Depth (AOD) and meteorological parameters (temperature and relative humidity) were carried out at a high altitude station, Sinhagad near Pune during the summer season of 2009.

Study Area

The observational station is situated on the historical fort at Sinhagad (180 311 N, 750 451 E), located on a mountain peak in the Western Ghat region on the Western coast of India at about 1400 m above sea level. There is an open view towards W while there is still some 100km to the coast with more mountains in between and the station cannot be regarded as a coastal site, although slightly more exposed to westerly winds from Arabian Sea than Pune. The nearest city, Pune is at about 40Km to the NE. The area is very sparsely populated, with no major human activity. The only source of pollution at this site is occasional wood burning in connection with cocking and some vehicular activity from tourists which is restricted up to the entrance of fort. Observations were carried out at the highest location on this site during 24th Apr to 1st May 2009.

Instrumentation and Sampling Techniques

BC measurements by Aethalometer

Continuous observations on BC aerosols were carried out by using an Aethalometer (AE-42, Magee Scientific, USA). In this method, atmospheric air is pumped through an inlet at the flow rate of about 3 LPM, which impinges on a quartz micro fiber strip. A light beam from a high intensity LED lamp is transmitted through the sample deposit on the filter strip, at 880 nm. The measurement of the attenuation of light beam is linearly proportional to the amount of BC deposited on filter strip. Observations were recorded at the time base of 5 minute interval.

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Size Differentiated Aerosols by GRIMM Aerosol Spectrometer

Data on size separated (PM10, PM2.5 and PM1.0) aerosols were obtained using an Aerosol Size Spectrometer (GRIMM, Model 1.108). This portable instrument gives single particle counts or masses and size classifications in 15 size interval (from 0.30 to > 20 μm size) in real time. This equipment has high speed counters with a resolution of 1 count/liter independent from wind direction with a built-in flow-controlled pump. The sample air goes into the high resolution optical cell in such a way, that one particle after the other can cross the laser illuminated optical volume. Each single particle passing the laser generates a scatter signal, which is collected at 90° scattering angle on a mirror and a photodiode. Observations were recorded for every 1 minute interval.

Aerosol Optical Depths (AOD) by MICROTOPS

The Solar Light microprocessor-controlled total ozone portable spectrometer (MICROTOPS-II) was used to measure the AOD at the wavelengths 380, 440, 500, 675, 870 and 1020nm. The sun-photometer works on the principle of measuring the surface- reaching solar radiation intensity at the specified wavelength bands and converts to optical depth based on the knowledge of the corresponding intensities at the TOA through Bouguer-Lambert-Beer law.

Results and Discussions

Concentrations and Day-night Variations of BC

The mean BC concentration was 1.07 ± 0.60 μg/m3 with maximum value as 3.98 μg/ m3 and minimum as 0.16 μg/m3. This concentration was about 2.7 times less than that observed at Pashan, a semi-urban location in Pune city, during the similar season. Pant et al (2006) have reported mean BC concentration of 1.36 ± 0.99 μg/m3 at Nainital, a high altitude location in North India during winter season. The daytime (06.00 am to 06.00 pm) mean BC concentration was 0.95 ± 0.39 μg/m3 whereas that during nighttime (06.00pm to 06.00am) was 1.08 ± 0.40 μg/m3, indicating more concentrations during nighttime hours (Day/Night ratio was 0.88). Fig. 19(a) shows the hourly variation of BC at Sinhagad compared with that at Pune and Fig.1 (b) shows the difference between BC hourly variation during summer and winter at Sinhagad.

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As seen from Fig.1(a), hourly variation of BC showed bimodal distribution at both Pashan and Sinhagad however, the large difference in magnitudes is the manifestation of impact of anthropogenic activities at Pune. At Sinhagad, BC showed decreasing trend from midnight (12am) to morning with lowest concentration at 9 am (0.32μg/m3). Then after, it started increasing sharply and reached peak at 12 pm (1.66 μg/m3) which then reduced to 0.91 μg/m3 at 2 pm and then again started increasing gradually to reach another peak at 9 pm (1.80 μg/m3), followed by decreasing trend up to midnight and further up to morning hours. The diurnal amplitude of BC concentration (difference between maximum and minimum concentration) was 1.48 μg/m3. This variation of BC is attributed mainly to the local burning activity in the nearby surrounding villages for

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F–P–5

Black Carbon and its Contribution to Aerosol Optical Depth over Kolkata on the Eastern IGP

Shantanu Kumar Pani1 and Shubha Verma1, 2

1Center for Oceans, Rivers, Atmosphere and Land Sciences

2Department of Civil Engineering, Indian Institute of Technology Kharagpur

Kharagpur,West Bengal,721302

Email: shantanukumarpani@gmail.com

ABSTRACT : The effect of black carbon (BC) on climate forcing is potentially important, but its estimates have large uncertainties due to lack of sufficient observational data. Black carbon is a particulate aerosol resulting from the incomplete combustion of fossil fuel, biomass, and biofuel. BC aerosols absorb the solar radiation reflected by the surface-atmosphere-cloud system and thus contribute to a positive forcing at the top-of-atmosphere (TOA), in contrast to non-BC aerosols (e.g. sulphates, nitrates, and organics), which reflect solar radiation, increasing the albedo of the planet and resulting in a negative forcing at TOA. Black carbon is a potent climate forcing agent, estimated to be the second largest contributor to global warming after carbon dioxide (CO2) (Ramanathan and Carmichael, 2008). Recent studies have shown the Indo-Gangetic Plain (IGP) over India as one of the regional hotspots of BC-induced atmospheric heating (Ramanathan et al., 2007) which could modify the regional climate.

Black carbon mass concentration has been found to be present in high concentration over Indo-Gangetic Plain (IGP) at Kharagpur (16 μgm-3) and Kanpur (13 μgm-3) during December 2004 (Nair et al., 2007). It is required to understand the seasonal variation of BC aerosols over the eastern IGP, including Kolkata (22.6°N, 88.42°E), which is an urban industrial location on the east coast of India.

In this paper, we present results from our measurements on black carbon aerosols mass concentration, at Kolkata, during post monsoon and winter 2009. Figure 1 represents diurnal variation of BC during days of measurements during November showing the highest surface mass concentration of BC during morning and evening with a lower value during afternoon. The high surface mass concentration of BC during morning is due to anthropogenic activities, including biomass burning for heating and cooking purpose, commencement of industrial activities, and rise in traffic density which leads to increase in emissions of BC. In addition, fumigation effect causes aerosols in the nocturnal residual layer mixed up with those near the surface. Low values of BC during afternoon hours are due to the dispersion of aerosols due to the increase in boundary layer height. Diurnal variations of BC concentrations were found to be in the range of 0.6 μgm-3 to as high as 28 μgm-3 over the study area. The optical depth of BC estimated in the Optical Properties of Aerosols and Clouds (OPAC) model (Hess et al., 1998) using the measured mass concentration showed the values in the range 0.12 to 0.25. The contribution of BC to the measured submicron mass concentration is 5%, while to the AOD is estimated to be as

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high as 30%. The paper will present detailed analysis on measured surface mass concentration of BC during post monsoon and winter season over Kolkata, its contribution to the AOD, and radiative effects.

Figure 2. Black carbon contribution to AOD

References

Hess M., P. Koepke, and I. Schult, Optical properties of aerosols and clouds: The software package OPAC, Bull. Am. Meteorol. Soc., 79, 831–844, 1998.

Nair Vijayakumar S., K. Krishna Moorthy, Denny P. Alappattu, P. K. Kunhikrishnan, Susan George, Prabha R. Nair, S. Suresh Babu, B. Abish, S. K. Satheesh, S. N. Tripathi, K. Niranjan, B. L. Madhavan, V. Srikant, C. B. S. Dutt, K. V. S. Badarinath, and R. Ramakrishna Reddy, Wintertime aerosol characteristics over

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the Indo-Gangetic Plain (IGP): Impacts of local boundary layer processes and long-range transport, J. Geophys. Res., 112, D13205, doi: 10.1029/2006JD008099, 2007.

Ramanathan V., F. Li, M. V. Ramana, P. S. Praveen, D. Kim, C. E. Corrigan, H. Nguyen, Elizabeth A. Stone, James J. Schauer, G. R. Carmichael, Bhupesh Adhikary and S. C. Yoon, Atmospheric brown clouds: Hemispherical and regional variations in long-range transport, absorption and radiative forcing. J. Geophys. Res., 112, doi: 10.1029/2006JD008124, 2007.

Ramanathan V. and G. Carmichael, Global and regional climate changes due to black carbon, nature geoscience, Nature Geoscience, 1, doi: 10.1038/ngeo156, 221 – 227, 2008.

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Diurnal and Seasonal Variation of Black Carbon and Aerosols over Dehradun

Yogesh Kant and V.K Dadhwal

Indian Institute of Remote Sensing (NRSC), ISRO, Dept. of Space,

Govt. of India,4 Kalidas Road, Dehradun

In the recent years, there has been an emphasis on study of direct and indirect influence of aerosols on the climate. Aerosols enhance the back scattering of solar radiation leading to negative radiative forcing while the absorbing black carbon (BC) aerosols leads to the positive effect. Black carbon is emitted into the atmosphere as a by-product of combustion processes such as fossil fuels, vegetation burning, industrial emissions, motor vehicle and aircraft exhausts and are generally in the sub-micron size region and are considered as tracers of anthropogenic impact on environment. The principal contributor in the atmospheric radiative forcing and climate change is black carbon (Chung et al., 2005; Jones et al., 2005). It has been reported that the global mean clear sky radiative forcing at the top of the atmosphere due to BC ranges from + 0.27 to + 0.54 Wm-2 (Jacobson, 2001). There have been many studies over India documenting the seasonal and diurnal variation of BC concentration at different locations (Babu et al., 2002, Latha and Badarinth, 2003; Badarinth, et al., 2007; Tripathi et al., 2005; Safai et al., 2007). These measurements help us in understanding the temporal changes in BC characteristics associated with atmospheric patterns and quantify radiative forcing over the Indian region. In the present study aerosol loading and BC measurements were carried out for 2007 over Dehradun, a valley in the shiwalik hills. The diurnal and seasonal behaviors of BC and AOD were studied and their relation to the meteorological parameters was also examined. Traffic density at nearby places, local boundary layer and the air mass back trajectory for possible transport has also been studied.

It was observed that during summer periods a slight increase in AOD is observed at longer wavelengths suggesting presence of high concentration of coarse mode particles. Mean AOD (at 500 nm) of 0.35 + 0.06 and 0.43 + 0.08 was observed for winter & summer months respectively. The aerosol loading was observed to be high during summer period due to the air mass coming from desert region in the far west direction. The annual average BC concentration observed was found to be 4.3 + 0.62 μgm-3. Diurnal variation of BC shows a gradual build up in the morning hours between 0600 to 0900 local time and in evening from 1900 to 2200 hrs local time while low concentration is observed during day & night time. The seasonal variation of BC reveals that the average concentration during January is maximum (10.5 g m-3) and decreases gradually till August (2.382 g m- 3) and increases thereafter. The variation of the mean monthly BC with total monthly rainfall shows that during the months (particularly monsoon period June to August) of heavy rainfall, the BC concentration decreases and increases during the dry months. The average concentration are found to be maximum (5.0 g m-3) during December, January followed by summer period (4.9 g m-3) (March, April, May) followed by post-monsoon

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period (3.04 g m-3) (September, October, November) and minimum during monsoon period (2.8 g m-3) (June, July, August). The analysis of traffic density measured at nearby places in the city shows that it has direct influence on the BC concentration. BC concentration increases more than three times during morning and evening compared to afternoon and night hours. Seasonal variations of BC shows high concentration during winter dry season associated with the air masses predominantly coming from Indo-Gangetic plain rich in carbonaceous aerosols and minimum during monsoon season due to wash out. The BC concentration is found to have relationship with anthropogenic activities, boundary layer dynamics and biomass burning which has been observed by the MODIS fire data in and around the region. BC concentration were positively correlated with diurnal temperature range and negatively correlated with rainfall and humidity.

Figure 1. Variation of AOD at 500 nm over Dehradun for the year 2007

Figure 2. Mean monthly BC concentration and its relation with total monthly rainfall, mean monthly wind speed, wind director and temperature range

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IASTA-2010

F–P–7

Measurements of Aerosol Black Carbon at an Urban Site in Southern India

Aswathy V Nair1, K. Mohan Kumar2 and S.K. Satheesh1

1Centre for Atmospheric and Oceanic Sciences Indian Institute of Science, Bangalore-560012, India.

2Department of Atmospheric Sciences, Cochin University of Science & Technology, Cochin

Email: aswathy.india06@gmail.com

Aerosols are suspended particulates in the atmosphere and have implications for climate and health through different mechanisms. Several studies have suggested that aerosols may be mitigating global warming by increasing the planetary albedo, although the sign and magnitude of aerosol effects on climate are still uncertain as outlined in the International Panel of Climate Change (IPCC) reports. Among the various aerosol types, black carbon (BC) aerosols assume at most importance due to its high absorption characteristics. In addition to exerting its own radiative impact, black carbon aerosol can substantially contaminate other aerosol species thereby alter the radiaitve properties of entire aerosol system (Babu et al., 2002).

In the present study, changes in the response of near surface aerosol properties and their association with meteorological parameters have been studied during entire 2008 over a tropical urban environment, Bangalore in southern India. It was observed that BC exhibits well defined diurnal (Fig. 1a-c) and seasonal variations (Fig. 2). Diurnal variations of BC showed a gradual build up of BC concentration from morning and a sharp peak occurs between 7:00 and 9:00 local time (almost an hour after the local sunrise) and a nocturnal peak from 20:00 to 23:00 local time. Lowest mass concentration was observed around 1400 hrs. Our investigations show that major factor affecting the aerosol concentration is the temperature of the surface layer and boundary layer dynamics (Babu and Moorthy, 2002). The nocturnal boundary layer is shallower than its daytime counter part by a factor of three and as the wind speeds are lower during night, there is a rapid reduction in the ventilation coefficient (Stull, 1988). This results in confinement of BC aerosol close to Earth’s surface.

May is representative of pre-monsoon season. The dashed line in Fig. 1 represents the monthly average sunrise and sunset times corresponding to May. Diurnal variation observed for monsoon period is shown using July as typical month. Compared with the pre-monsoon period there is an overall reduction in the BC mass concentration over the monsoon period (Fig. 1b). This is mainly because of the wash out due to monsoon rainfall (Vinoj et al., 2004). Even though there is an overall reduction in BC during monsoon months, still there exists a clear diurnal pattern with two peaks, one during the morning and second one during late evening. Compared to the other two seasons the night-time BC concentration is significantly lower during post-monsoon season (Fig. 1c). But the early morning concentration is higher than the monsoon month.

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July was compensated by the excess rainfall during September (IMD report, 2008). Large increase in BC concentration (by as much as factor of 3 to 4) was observed during Diwali period (Fig. 3) as also reported in earlier studies (Babu and Moorthy, 2001).

Correlation analysis shows that monthly averaged BC is negatively correlated with wind speed and temperature. Scatter plot of wind speed and corresponding BC mass concentration yielded high negative correlation with a correlation coefficient of -0.82. Significance is calculated using t-test and was found that correlation is significant at 99.9%. Below a wind speed of 2 m s-1, no correlation was found where as correlation increased substantially after 2 m s-1. Our study demonstrates the role of meteorological parameters on surface BC concentration. In general, our measurements indicate that BC concentration at Bangalore is lower than those reported for other urban sites in India.

References

Babu. S.S, and Krishna Moorthy, K. (2001) Anthropogenic impact on aerosol black carbon mass concentration at a tropical coastal station: A case study, Current Science, 81, No. 9, 10-14.

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Babu, S. S., and Krishna Moorthy, K. (2002) Aerosol black carbon over a tropical coastal station in India, Geophysical Research Letters, 29, NO. 23, 2098, doi:10.1029/2002GL015662.

Babu, S. S., S.K Satheesh and Krishna Moorthy, K. (2002) Aerosol radiative forcing due to enhanced black carbon at an urban site in India, Geophysical Research Letters, 29, NO. 18, 1880, doi:10.1029/ 2002GL015826.

Stull, R. B (1988), An introduction to Boundary Layer Meteorology, Kluwer Academic publishing, New York, 18.

Vinoj, V and Satheesh, S. K (2003), Measurements of aerosol optical depth over Arabian Sea during summer monsoon season, Geophysical Research Letters, 30, NO. 5, 1263, doi:10.1029/2002GL016664.

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