Size distributions and chemical characterization of water-soluble organic aerosols over the western North Pacific in summer

Abstract

Size-segregated aerosol samples were collected over the western North Pacific in summer 2008 to investigate marine biological contribution to organic aerosols. The samples were analyzed for organic carbon (OC), water-soluble organic carbon (WSOC), and water-soluble organic compounds including diacids (C 2 -C 9), ω-oxocarboxylic acids, and α-dicarbonyls as well as methanesulfonic acid (MSA). The average concentrations of OC and oxalic acid (C 2) were approximately two to three times larger in marine biologically more influenced aerosols, defined by the concentrations of MSA and azelaic acid (C 9), than in less influenced aerosols. WSOC, which showed a statistically significant correlation with MSA, accounted for 15-21% of total mass of the components determined in the submicrometer range of biologically more influenced aerosols. These values are comparable to those of water-insoluble organic carbon (WIOC) (∼14-23%), suggesting that organic aerosols in this region are enriched in secondary organic aerosols (SOA) linked to oceanic biological activity. In these aerosols, substantial fractions of C 2 -C 4 diacids were found in the submicrometer size range. Positive correlations of oxalic acid with C 3 -C 5 diacids and glyoxylic acid suggest that secondary production of oxalic acid occurs possibly in the aqueous aerosol phase via the oxidation of longer-chain diacids and glyoxylic acid in the oceanic region with higher biological productivity. We found similar concentration levels and size distributions of methylglyoxal between the two types of aerosols, suggesting that formation of oxalic acid via the oxidation of methylglyoxal from marine isoprene is insignificant in the study region. Copyright 2010 by the American Geophysical Union.