) data set on the chemical composition of ambient aerosols collected from an urban location (Kanpur) in the Indo-Gangetic Plain (IGP) and suggests that the varying strength of the regional emission sources, boundary layer dynamics, and formation of secondary aerosols all contribute significantly to the temporal variability in the mass concentrations of elemental carbon (EC), organic carbon (OC), and water-soluble OC (WSOC). On average, carbonaceous aerosols contribute nearly one third of the PM 10 mass during winter, whereas their fractional mass is only ∼10% during summer. A three-to four-fold increase in the OC and K + concentrations during winter and a significant linear relation between them suggest biomass burning (wood fuel and agricultural waste) emission as a dominant source. The relatively high OC/EC ratio (average: 7.4 ± 3.5 for n = 66) also supports that emissions from biomass burning are overwhelming for the particulate OC in the IGP. The WSOC/OC ratios vary from 0.21 to 0.70 over the annual seasonal cycle with relatively high ratios in the summer, suggesting the significance of secondary organic aerosols. The long-range transport of mineral aerosols from Iran, Afghanistan, and the Thar Desert (western India) is pronounced during summer months. The temporal variability in the concentrations of selected inorganic constituents and neutralization of acidic species (SO 4 2− and NO 3 − ) by NH 4 + (dominant during winter) and Ca 2+ (in summer) reflect conspicuous changes in the source strength of anthropogenic emissions.Citation: Ram, K., M. M. Sarin, and S. N. Tripathi (2010), A 1 year record of carbonaceous aerosols from an urban site in the Indo-Gangetic Plain: Characterization, sources, and temporal variability,

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Abstract.A long-term study, conducted from February 2005 to July 2008, involving chemical composition and optical properties of ambient aerosols from a high-altitude site (Manora Peak: 29.4 • N, 79.5 • E, ∼1950 m a.s.l.) in the central Himalaya is reported here. The total suspended particulate (TSP) mass concentration varied from 13 to 272 µg m −3 over a span of 42 months. Aerosol optical depth (AOD) and TSP increase significantly during the summer (AprilJune) due to increase in the concentration of mineral dust associated with the long-range transport from desert regions (from the middle-East and Thar Desert in western India). The seasonal variability in the carbonaceous species (EC, OC) is also significantly pronounced, with lower concentrations during the summer and monsoon (July-August) and relatively high during the post-monsoon (September-November) and winter (December-March). On average, total carbonaceous aerosols (TCA) and water-soluble inorganic species (WSIS) contribute nearly 25 and 10% of the TSP mass, respectively. The WSOC/OC ratios range from 0.36 to 0.83 (average: 0.55 ± 0.15), compared to lower ratios in the IndoGangetic Plain (range: 0.35-0.40), and provide evidence for the enhanced contribution from secondary organic aerosols. The mass fraction of absorbing EC ranged from less than a percent (during the summer) to as high as 7.6% (during the winter) and absorption coefficient (b abs , at 678 nm) varied between 0.9 to 33.9 Mm −1 (1 Mm −1 =10 −6 m −1 ). A significant linear relationship between b abs and EC (µgC m −3 ) yields a slope of 12.2 (± 2.3) m 2 g −1 , which is used as a measure of the mass absorption efficiency (σ abs ) of EC.