Abstract
The aerosol samples were analyzed for water-soluble dicarboxylic acids (C2–C12) and related compounds (ketocarboxylic acids and α-dicarbonyls), as well as organic carbon, elemental carbon and water soluble organic carbon. The contributions of total diacids to total aerosol carbon content during wintertime were 1.7 % and 1.8%, for day and night, respectively; whereas during summer the contributions were significantly reduced. Molecular distributions of diacids demonstrated that oxalic (C2) acid was the most abundant species followed by C4 and C3 diacids. The annual average concentrations of total diacids (433 ± 108 ng m-3), ketoacids (48 ± 23 ng m-3), and α-dicarbonyls (9 ± 4 ng m-3) were comparable to those from other Asian megacities such as Tokyo, Beijing and Hong Kong. During summer season most of the organic species were several times more abundant than in winter. Phthalic acid, which originates from oxidation of polycyclic aeromatic hydrocarbons such as naphthalene was found to be 7 times higher in summer. This feature has not been reported previously in atmospheric aerosols. Glyoxal and glyoxylic acid are intermediates in the formation of oxalic acid for winter months. In contrast, during summer months, succinic acid was found to be decomposed to malonic acid and then to oxalic acid following the oxidative degradation of biogenic unsaturated fatty acids. Based on molecular distributions and backward air mass trajectories, we found that diacids and related compounds in Himalayan aerosols were influenced by the anthropogenic activities from highly populated Indo-Gangetic plain areas.
