Chemical Characteristics of Aerosols from Distinct Environments over the Indian Region: Heterogeneity in Distribution and Sources of Carbonaceous Aerosols

A comprehensive picture of the chemical characteristics of near-surface aerosols (PM10) from distinct geographic environments over the Indian region is presented with emphasis on carbonaceous aerosols. The regions of study were coastal, inland, coastal industrial, semiarid, coastal oceanic, and deep oceanic. Among the measured chemical species, the characteristics of carbonaceous species (organic carbon (OC) and elemental carbon (EC)) in terms of the seasonal variations in their mass concentration in accordance with the changing air-mass patterns, ambient meteorological conditions, and source characteristics were examined in detail. The carbonaceous components exhibited the highest concentration during the winter period over all of the study regions irrespective of the geographic distinctiveness and varied regional meteorology. The chemical composition of aerosols during the winter period revealed SO42- and OC as the major chemical species with SO42- dominating over southern peninsular India and oceanic regions, while OC dominated over northern India. Decrease in the mass fraction of OC and increase in SO42- were observed in the aerosol chemical composition for air-mass originating from hotspot regions such as the Indo Gangetic Plain and undergoing long-range transport to background downwind sites and oceanic environments. Progressive conversion of SO2 to SO42- under favorable ambient conditions during long-range transport resulted in a higher SO42- mass fraction over background sites. The highly water-soluble nature of OC (>70%) was observed as a result of oxidative aging of organics during long-range transport over oceanic regions directly influenced by continental outflow.