Abstract. Organic molecular composition of PM 10 samples, collected at Chennai in tropical India, was studied using capillary gas chromatography/mass spectrometry. Fourteen organic compound classes were detected in the aerosols, including aliphatic lipids, sugar compounds, lignin products, terpenoid biomarkers, sterols, aromatic acids, hydroxy-/polyacids, phthalate esters, hopanes, Polycyclic Aromatic Hydrocarbons (PAHs), and photooxidation products from biogenic Volatile Organic Compounds (VOCs). At daytime, phthalate esters were found to be the most abundant compound class; however, at nighttime, fatty acids were the dominant one. Di-(2-ethylhexyl) phthalate, C 16 fatty acid, and levoglucosan were identified as the most abundant single compounds. The nighttime maxima of most organics in the aerosols indicate a land/sea breeze effect in tropical India, although some other factors such as local emissions and long-range transport may also influence the composition of organic aerosols. However, biogenic VOC oxidation products (e.g., 2-methyltetrols, pinic acid, 3-hydroxyglutaric acid and β-caryophyllinic acid) showed diurnal patterns with daytime maxima. Interestingly, terephthalic acid was maximized at nighttime, which is different from those of phthalic and isophthalic acids. A positive relation was found between 1,3,5-triphenylbenzene (a tracer for plastic burning) and terephthalic acid, suggesting that the field burning Correspondence to:K. Kawamura (kawamura@lowtem.hokudai.ac.jp) of municipal solid wastes including plastics is a significant source of terephthalic acid. Organic compounds were further categorized into several groups to clarify their sources. Fossil fuel combustion (24-43%) was recognized as the most significant source for the total identified compounds, followed by plastic emission (16-33%), secondary oxidation (8.6-23%), and microbial/marine sources (7.2-17%). In contrast, the contributions of terrestrial plant waxes (5.9-11%) and biomass burning (4.2-6.4%) were relatively small. This study demonstrates that, in addition to fossil fuel combustion and biomass burning, the open-burning of plastics in urban area also contributes to the organic aerosols in South Asia.

[1] Tropical aerosol (PM 10 ) samples (n = 49) collected from southeast coast of India were studied for water-soluble dicarboxylic acids (C 2 -C 12 ), ketocarboxylic acids (C 2 -C 9 ), and a-dicarbonyls (glyoxal and methylglyoxal), together with analyses of total carbon (TC) and water-soluble organic carbon (WSOC). Their distributions were characterized by a predominance of oxalic acid followed by terephthalic (t-Ph), malonic, and succinic acids. Total concentrations of diacids (227-1030 ng m −3 ), ketoacids (16-105 ng m −3 ), and dicarbonyls (4-23 ng m −3 ) are comparative to those from other Asian megacities such as Tokyo and Hong Kong. t-Ph acid was found as the second most abundant diacid in the Chennai aerosols. This feature has not been reported previously in atmospheric aerosols. t-Ph acid is most likely derived from the field burning of plastics. Water-soluble diacids were found to contribute 0.4%-3% of TC and 4%-11% of WSOC. Based on molecular distributions and backward air mass trajectories, we found that diacids and related compounds in coastal South Indian aerosols are influenced by South Asian and Indian Ocean monsoons. Organic aerosols are also suggested to be significantly transported long distances from North India and the Middle East in early winter and from Southeast Asia in late winter, but some originate from photochemical reactions over the Bay of Bengal. In contrast, the Arabian Sea, Indian Ocean, and South Indian continent are suggested as major source regions in summer. We also found daytime maxima of most diacids, except for C 9 and t-Ph acids, which showed nighttime maxima in summer. Emissions from marine and terrestrial plants, combined with land/sea breezes and in situ photochemical oxidation, are suggested especially in summer as an important factor that controls the composition of water-soluble organic aerosols over the southeast coast of India. Regional emissions from anthropogenic sources are also important in megacity Chennai, but their influence is weakened due to the dispersion caused by dynamic land/sea breeze on the coast.Citation: Pavuluri, C. M., K. Kawamura, and T. Swaminathan (2010), Water-soluble organic carbon, dicarboxylic acids, ketoacids, and a-dicarbonyls in the tropical Indian aerosols,

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17To better understand the origins of aerosol nitrogen, we measured concentrations of total 18 nitrogen (TN) and its isotopic ratios (δ 15 N) in tropical Indian aerosols (PM 10 and for the particles emitted from point sources (including a laboratory study), as well as the 24 δ 15 N ratios of cow-dung samples (this study), we found that the atmospheric aerosol N in 25Chennai has two major sources; animal excreta and bio-fuel/biomass burning from South and 26Southeast Asia. We demonstrate that a gas-to-particle conversion of NH 3 to NH 4 HSO 4 and 27 (NH 4 ) 2 SO 4 and the subsequent exchange reaction between NH 3 and NH 4 + are responsible for 28 the isotopic enrichment of 15 N in aerosol nitrogen. 29 30

Abstract. To better characterize the tropical aerosols in Indian region, PM 10 samples collected from Chennai, India (13.04 • N; 80.17 • E) were analyzed for carbonaceous and water-soluble ionic components. Concentration ranges of elemental carbon (EC) and organic carbon (OC) were 2.4-14 µg m −3 (ave. 6.5 µg m −3 ) and 3.2-15.6 µg m −3 (ave. 9.1 µg m −3 ) in winter samples whereas they were 1.1-2.5 µg m −3 (ave. 1.6 µg m −3 ) and 4.1-17.6 µg m −3 (ave. 9.7 µg m −3 ) in summer samples, respectively. Concentration of secondary organic carbon (SOC) retrieved from EC-tracer method was 4.6±2.8 µg m −3 in winter and 4.3±2.8 µg m −3 in summer. OC accounted for 38.5±14 % (n = 49) of combined concentrations of carbonaceous and ionic components in PM 10 . We also found that OC concentrations are generally higher than those of SO 2− 4 (8.8±2.5 µg m −3 and 4.1±2.7 µg m −3 in winter and summer, respectively), which was the most abundant ionic species (57 %) followed by NH + 4 (15 %) >NO − 3 >Cl − >K + >Na + >Ca 2+ >MSA − >Mg 2+ . The mass fractions of EC, organic matter (OM) and ionic species varied seasonally, following the air mass trajectories and corresponding source strength. Based on mass concentration ratios of selected components and relations of EC and OC to marker species, we found that biofuel/biomass burning is a major source of atmospheric aerosols in South and Southeast Asia. The high concentrations of SOC and WSOC/OC ratios (ave. 0.45; n = 49) as well as good correlations between SOC and WSOC suggest that the secondary production of organic Correspondence to: K. Kawamura (kawamura@lowtem.hokudai.ac.jp) aerosols during long-range atmospheric transport is also significant in this region. This study provides the baseline data of carbonaceous aerosols for southern part of the Indian subcontinent.

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