Dicarboxylic acids, ketocarboxylic acids, and dicarbonyls in the urban atmosphere of China

PM_2.5 samples from 14 Chinese cities during winter and summer of 2003 were analyzed for 29 water-soluble organic species including diacids, ketoacids and dicarbonyls using a capillary GC, and GC/MS. Homologous series of α,Ω-dicarboxylic acids (C₂-C₁₂) and Ω-oxocarboxylic acids (C₂-C₉) were detected as well as aromatic (phthalic) acid, α-ketoacid (pyruvic acid) and α-dicarbonyls (C₂-C₃). Molecular distributions of diacids demonstrated that oxalic (C₂) acid was the most abundant species followed by C₃ or C₄ diacids. Higher carbon number diacids were less abundant. C₂ diacid constituted 42-74% of total diacids (211-2162 ng m^-3), corresponding to 0.15-2.83% of PM_2.5 mass. In winter, the highest concentrations were observed in the southern city of Guangzhou (1886 ng m^-3), while the lowest concentrations were observed in the northwest city of Jinchang (388 ng m^-3). In summer, the highest concentrations were found in the northern city of Beijing (1598 ng m^-3), whereas the lowest concentrations were found in Jinchang (223 ng m^-3). Spatial variations of water-soluble diacids were characterized by higher concentrations in the south and lower concentrations in the north during winter whereas highest concentrations were observed in the north and midwest during summer. These spatial and seasonal distributions are consistent with photochemical production and the subsequent accumulation under different meteorological conditions.