Dicarboxylic acids, ketocarboxylic acids and glyoxal in the marine aerosols collected during a round-the-world cruise

摘要

This study investigated spatial distributions of water-soluble dicarboxylic acids and related compounds in the marine aerosols collected at low- to mid-latitudes in the Northern Hemisphere for a better understanding of the photochemical aging of organic aerosols during long-range transport. Their molecular distributions were characterized by the predominance of oxalic acid (C_2) followed by malonic (C_3) and succinic (C_4) acids, except for one sample (QFF114, C_2 > C_4> C_3) that was collected in the western North Pacific with a heavy influence of biomass burning. Concentration ranges of diacids, ketoacids (including glyoxylic acid and pyruvic acid), and glyoxal were 17-718 ng m~(-3) (average 218 ng m~(-3)), 0.40-72 ng m~(-3) (23 ng m~(-3)), and 0.16-19 ng m~(-3) (3.3 ng m~(-3)), which account for 3.6-23% (14%), 0.09-2.3% (1.3%), and 0.04-0.45% (0.19%) of organic carbon (OC) in the marine aerosols, respectively. Positive correlations were observed between OC and diacids/ketoacids. Positive correlations were also found between biogenic secondary organic aerosol (SOA) tracers (e.g., 2-methylglyceric acid) and diacids/ketoacids, suggesting a significant contribution of biogenic secondary source. The spatial distributions of diacids exhibited higher loadings over the coastal/tropical regions than the open oceans, which are similar to those of the concentration ratios of malonic/succinic (C3/C4) and adipic/azelaic (C_6/C_9), indicating a more significant influence of anthropogenic sources over the coastal regions than the remote oceans. However, the concentration ratios of oxalic acid to levoglucosan, a biomass-burning tracer, and to C_(29) n-alkane, a tracer for terrestrial biogenic emission showed higher values over the open oceans than the coastal regions, suggesting a continuous production of oxalic acid during long-range atmospheric transport. This study indicates that the long-range transport of primary and secondary aerosols of continental origin and photo-oxidation/aerosol aging are important factors controlling the organic chemical composition of aerosol particles in the marine atmosphere.