Diurnal changes in the distribution of dicarboxylic acids, ketocarboxylic acids and dicarbonyls in the urban Tokyo atmosphere

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Secondary organic aerosol in the urban atmosphere is an important issue from aviewpoint of not only air pollution but also regional and global atmospheric environment. Tobetter understand the production of water-soluble organic aerosols, we analyzed atmosphericparticles collected in time-series in Tokyo for dicarboxylic acids (C2-C10), ketocarboxylic acids(C2-C4) and a-dicarbonyls (C2-C3) using a GC and GC/MS. Here, we report, for the first time,diurnal distributions of dicarboxylic acids, ketoacids and dicarbonys in the urban atmosphere.Oxalic acid was found as the most abundant species, followed by malonic, succinic, pyruvicand glyoxylic acids. Total diacids showed a concentration maximum in daytime (11-14 h) witha dynamic change in their molecular composition especially in summer samples. Relativeabundances of unsaturated (maleic, methylmaleic and phthalic) and some saturated(methylsuccinic and adipic) species increased in the morning (8-11 h) whereas those of oxalicacid decreased down to 35 % in 8-11 h but increased up to 58 % toward 17-20 h. The diurnalvariations are interpreted by photochemical production of diacids, where unsaturated and somesaturated species are preferentially generated early in the morning via photo-oxidation ofaromatic hydrocarbons and cyclic olefins and further oxidized to oxalic acid in the afternoon.
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