ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-12-6645-2012 Seasonal variations of water-soluble organic carbon, dicarboxylic acids, ketocarboxylic acids, and α-dicarbonyls in Central Himalayan aerosols Hegde P. 1 2 Kawamura K. 1 Institute of Low Temperature Science, Hokkaido University, Sapporo, Japan Space Physics Laboratory, Vikram Sarabhai Space Centre, Trivandrum, India 26 07 2012 12 14 6645 6665 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/12/6645/2012/acp-12-6645-2012.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/12/6645/2012/acp-12-6645-2012.pdf

Aerosol samples were collected from a high elevation mountain site (Nainital, India; 1958 m a.s.l.) in the central Himalayas, a location that provides 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 (C<sub>2</sub>-C<sub>12</sub>) 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 were significantly smaller during summer. Molecular distributions of diacids revealed that oxalic (C<sub>2</sub>) acid was the most abundant species followed by succinic (C<sub>4</sub>) and malonic (C<sub>3</sub>) acids. The average concentrations of total diacids (433±108 ng m<sup>−3</sup>), ketoacids (48±23 ng m<sup>−3</sup>), and α-dicarbonyls (9±4 ng m<sup>−3</sup>) were similar to those from large Asian cities such as Tokyo, Beijing and Hong Kong. During summer 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 before in atmospheric aerosols. Based on molecular distributions and air mass backward trajectories, we conclude that dicarboxylic acids and related compounds in Himalayan aerosols are derived from anthropogenic activities in the highly populated Indo-Gangetic plain areas.

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