Molecular distributions of water soluble dicarboxylic acids in marine aerosols over the Pacific Ocean including tropics

Remote marine aerosols collected over the western North to equatorial Pacific (34 degrees N-14 degrees S, 140 degrees E-150 degrees W) were studied far low molecular weight dicarboxylic acids using a capillary gas chromatography (CC) and GC/mass spectrometer, and for total carbon and nitrogen contents. Homologous series of dicarboxylic acids (C2-C10) including keto- and hydroxy-dicarboxylic acids were detected in the samples with a concentration range of 10-250 ng m(-3) (average 63 ng m(-3) and median 44 ng m(-3)). Their molecular distributions showed a predominance of oxalic acid (C2), followed by malonic acid (C3) The smallest diacid (C2, 6.5-161 ng m(-3) with average 40 ng m(-3) and median 17 ng m(-3))composed 45-75% (average 65%) of the total diacids. The diacids showed higher concentrations in the western Pacific rim near Japanese islands and showed lower concentrations in the central and tropical Pacific. However, relative abundances of the diacid-carbon in the total aerosol carbon (1.1-15.8%) were found to be higher in the equatorial central Pacific. These diacids are probably in situ produced in the Pacific atmosphere by photochemical oxidation of gaseous and particulate precursors. Results of principal component analysis of individual diacid, coupled with an information on photochemical reactions, further support that C2 and C3 diacids are likely produced by the oxidation of C4 and longer-chain diacids, whereas longer-chain (C5-C10) diacids are produced through the oxidation of semivolatile fatty acids which are also oxidation products of unsaturated fatty acids. Concentrations of total C (0.069-5.27 mu g m(-3) with average 0.39 mu g m(-3) and median 0.15 mu g m(-3)) and total N (0.026-1.44 mu g m(-3) with average 0.12 mu g m(-3) and median 0.077 mu g m(-3)) were generally higher over the western Pacific.