Organic and inorganic compositions of marine aerosols from East Asia: Seasonal variations of water-soluble dicarboxylic acids, major ions, total carbon and nitrogen, and stable C and N isotopic composition

摘要

Atmospheric particles were collected for one year (2001-2002) at a site Gosan on Jeju Island, South Korea. The samples were analyzed for water-soluble dicarboxylic acids and related compounds using a capillary GC and GC/MS. Total carbon and nitrogen contents, as well as their stable isotopic ratios, were also determined using elemental analyzer (EA) and EA/IR/MS, respectively. Elemental and isotopic analyses were also performed after the HCl vapor treatment of aerosol samples. The results demonstrate that calcium carbonate of dust origin was not a significant component, except for a few dust event samples. Carbonates most likely reacted with acidic species (such as H2SO4, HNO3 and organic acids) in the atmosphere during a long-range transport, and did not contribute to the total aerosol carbon, except for few strong dust episodes that occurred in spring. This study also demonstrates that nitrate and ammonium largely contribute to aerosol nitrogen and organic nitrogen is minor component in the Asian aerosols. Acidic aerosols enriched with sulfate likely adsorb NH3 gas that is emittedfrom soils in Asia whereas mineral dust particles containing carbonate may adsorb HNO3 and volatile organic acids.Homologous series of dicarboxylic acids (C2-C12) including unsaturated structures as well as ketocarboxylic acids (C2-C9) were detected in the aerosol samples with oxalic (C2) acid being the most abundant species followed by malonic (C3) or succinic (C4) acids. Total concentrations of diacids (130-2070 ng m-3) are one or two orders of magnitude greater thanthose reported for remote marine aerosols in the North Pacific, but are equivalent to those reported for urban aerosols. Very high concentrations of dusts (up to 880 mg m-3) and watersoluble dicarboxylic acids were often observed in early spring. However, their correlation (r=0.27) is not strong throughout the campaign. Although both mineral dusts and diacids are derived from the Asian continent, they originate from different sources and source regions. Diacids are probably emitted from urban sources in East Asia and produced by secondary photochemical oxidation of their precursors, whereas dusts are derived from the arid interior regions. This study provides evidence for photochemical production of water-soluble organic acids in East Asia and the western North Pacific rim.