||Latitudinal distributions of atmospheric dicarboxylic acids, oxocarboxylic acids, and α-dicarbonyls over the western North Pacific : Sources and formation pathways
Bikkina, Srinivas Kawamura, Kimitaka ,
Journal of geophysical research-atmospheres
5035 , 2015-05-28 , American Geophysical Union
The present study aims to assess the molecular distributions of water-soluble dicarboxylic acids (diacids: C-2-C-12), oxocarboxylic acids (C-2-C-9), and -dicarbonyls (glyoxal and methylglyoxal) in aerosols collected over the western North Pacific (WNP) during a summer cruise (August to September 2008). The measured water-soluble organics show pronounced latitudinal distributions with higher concentrations in the region of 30 degrees N-45 degrees N (average 63ngm(-3)) than 10 degrees N-30 degrees N (18ngm(-3)). Mass fraction of oxalic acid (C-2) in total aliphatic diacids (sigma C-2-C-12) showed higher values (7210%) in lower latitude (10 degrees N-30 degrees N) than that (5616%) in higher latitude (30 degrees N-45 degrees N), suggesting a photochemical production of C-2 due to an increased insolation over the tropical WNP. A similar trend was found in other diagnostic ratios such as oxalic to succinic (C-2/C-4) and oxalic to glyoxylic acid (C-2/C-2), which further corroborate an enhanced photochemical aging over the WNP. In addition, relative abundances of oxalic acid in total diacids showed a marked increase as a function of ambient temperature, supporting their photochemical production. Constantly low concentration ratios of adipic and phthalic acids relative to azelaic acid suggest a small contribution of anthropogenic sources and an importance of oceanic sources during the study period. Significant production of C-2 through oxidation of biogenic volatile organic compounds emitted from the sea surface is also noteworthy, as inferred from the strong linear correlations among water-soluble organic carbon, methanesulphonic acid, and oxalic acid. Sea-to-air emission of unsaturated fatty acids also contributes to formation of diacids over the WNP.