[1] Day-and nighttime aerosol samples were collected at an urban site in New Delhi, India, in winter 2006-2007. They were studied for low molecular weight dicarboxylic acids and related compounds, as well as total water-soluble organic carbon (TWSOC). High concentrations of diacids (up to 6.03 mg m À3 ), TWSOC, and OC were obtained, which are substantially higher than those previously observed at other urban sites in Asia. Daytime TWSOC/OC ratio (37%) was on average higher than that in nighttime (25%). In particular, more water-soluble OC (M-WSOC) to TWSOC ratio in daytime (50%) was twice higher than in nighttime (27%), suggesting that aerosols in New Delhi are photochemically more processed in daytime to result in more water-soluble organic compounds. Oxalic acid (C 2 ) was found as the most abundant dicarboxylic acid, followed by succinic (C 4 ) and malonic (C 3 ) acids. Contributions of C 2 to M-WSOC were greater (av. 8%) in nighttime than daytime (av. 3%). Positive correlations of C 2 with malic acid (hC 4 ), glyoxylic acid (wC 2 ), and relative humidity suggest that secondary production of C 2 probably in aqueous phase is important in nighttime via the oxidation of both longer-chain diacids and wC 2 . C 2 also showed a positive correlation with potassium (K + ) in nighttime, suggesting that the enhanced C 2 concentrations are associated with biomass/biofuel burning. More tight, positive correlation between less water-soluble OC (L-WSOC) and K + was found in both day-and nighttime, suggesting that L-WSOC, characterized by longer chain and/or higher molecular weight compounds, is significantly influenced by primary emissions from biomass/biofuel burning.

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Emission from field burning of agricultural crop residue is a common environmental hazard observed in northern India. It has a significant potential health risk for the rural population due to respirable suspended particulate matter (RSPM). A study on eight stage size segregated mass distribution of RSPM was done for 2 wheat and 3 rice crop seasons. The study was undertaken at rural and agricultural sites of Patiala (India) where the RSPM levels remained close to the National Ambient Air quality standards (NAAQS). Fine particulate matter (PM 2.5 ) contributed almost 55% to 64% of the RSPM, showing that, in general, the smaller particles dominated during the whole study period with more contribution during the rice crop as compared to that of wheat crop residue burning. Fine particulate matter content in the total RSPM increased with decrease in temperature. Concentration levels of PM 10 and PM 2.5 were higher during the winter months as compared to that in the summer months. Background concentration levels of PM 10 , PM 2.5 and PM 10À2.5 were found to be around 97AE21, 57AE15 and 40AE6 mg m À3, respectively. The levels increased up to 66, 78 and 71% during rice season and 51, 43 and 61% during wheat crop residue burning, respectively. Extensive statistical analysis of the data was done by using pair t-test. Overall results show that the concentration levels of different size particulate matter are greatly affected by agricultural crop residue burning but the total distribution of the particulate matter remains almost constant.