SEASONAL-CHANGES IN THE DISTRIBUTION OF DICARBOXYLIC-ACIDS IN THE URBAN ATMOSPHERE

Low molecular weight dicarboxylic acids have been studied in the urban aerosol samples collected from Tokyo atmosphere in 1988-1989, by using a capillary GC and GC-MS method employing a dibutyl ester derivatization technique. A homologous series of C2-C-10 dicarboxylic acids were detected in the aerosols, including straight-chain saturated, unsaturated, branched-chain, and hydroxylated species. Molecular distributions of the diacids demonstrated that oxalic (C2) acid was the most abundant throughout the four seasons, followed by C3 and C4 diacids: the C2 diacid comprised 37-69 % of the total diacid concentrations. The diacids with more carbon numbers were less abundant, although C6 and C9 diacids were relatively abundant. Total concentrations of the diacids ranged from 90 to 1370 ng m-3, which correspond to 0.06-1.1 % of the total aerosol mass. Their concentrations relative to aerosol mass showed a seasonal trend with a maximum in August. The C2-C4 diacid carbon normalized by aerosol total carbon also showed a strong seasonal change with a maximum in the summer and indicated a positive correlation with oxidant concentrations. Interestingly, lower diacids showed higher values for correlation coefficient (e.g., r = 0.80 for oxalic acid), suggesting a preferential production of low molecular weight dicarboxylic acids, especially, C2 diacid. Possible reaction mechanisms are discussed in relation to the preferential accumulation of lower diacids in the atmosphere.