Low Molecular-Weight Dicarboxylic and Fatty Acids Over the Northwestern Pacific and the Sea off East Asia During the ACE-Asia Campaign

Sampling of dicarboxylic and fatty acids was conducted from March 15 to April 20, 2001 on R/V NOAA Ronald H. Brown over the Northwestern Pacific, East China Sea and the Sea of Japan, as part of the ACE-Asia campaign. During the cruise, aerosol particles were collected on pre-combusted quartz fiber filters using a high volume air sampler, and organic acids in gas and particles were collected separately using an annular denuder with a backup quartz filter. In addition, MOUDI impactor was used for size-segregated aerosols. The collected samples were analyzed for water and ethyl-acetate extractable organic compounds such as low molecular-weight dicarboxylic acids and fatty acids using capillary GC and GC/MS. Throughout the cruise, oxalic acid, followed by malonic and succinic acids, was found to be the most dominant species. For oxalic acid, concentrations as high as 1 μ g m^-3 was observed occasionally at sea off East Asia. Chemical transport model calculations predicted high sulfate concentrations in the regions where oxalic acid concentrations were high, suggesting that oxalic acid should have been strongly influenced by anthropogenic emissions from the Asian continent. This is consistent with our hypothesis that the main source of oxalic and some other dicarboxylic acids are anthropogenic in the East Asia region. The relative abundances of dicarboxylic acids and fatty acids between gas and particles were obtained by analyses of denuder samples. For oxalic acid, 65-90 % were present in particles, whereas some fatty acids were detected only in particles. Molecular compositions, gas to particle ratios, and size distributions of the organic aerosol particles obtained by this study would provide information of sources, chemical processes and transport, which will be discussed in this presentation.