Seasonal variations of water-soluble organic carbon, dicarboxylic acids, ketoacids, and α-dicarbonyls in the central Himalayan aerosols

Abstract

Abstract. Aerosol samples were collected from a high elevation mountain site (Nainital, India; 1958 m a.s.l.) in the central Himalayas, which provide an isolated platform above the planetary boundary layer to better understand the composition of the remote continental troposphere. The 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 dicarboxylic acids to total aerosol carbon during wintertime were 1.7 and 1.8%, for day and night, respectively whereas they significantly reduced during summer. Molecular distributions of diacids demonstrated that oxalic (C2) acid was the most abundant species followed by C4 and C3 diacids. The 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 similar to those from Asian cities 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 aromatic hydrocarbons such as naphthalene, was found to be 7 times higher in summer than winter. This feature has not been reported in atmospheric aerosols. Based on molecular distributions and air mass backward trajectories, we report that dicarboxylic acids and related compounds in Himalayan aerosols are influenced by the anthropogenic activities from highly populated Indo-Gangetic plain areas.