Dicarboxylic acids, ketocarboxylic acids and dicarbonyls in the urban roadside area of Hong Kong

Homologous dicarboxylic acids (C2–C12), ketocarboxylic acids (ωC2–ωC9, pyruvic acid) and dicarbonyls (glyoxal and methylglyoxal) have been studied in the urban aerosol samples (PM2.5) collected from the Hong Kong roadside atmosphere during winter and summer of 2003 using a capillary GC and GC-MS method. The concentrations of total dicarboxylic acids, ketocarboxylic acids, and α-dicarbonyls were higher in winter than in summer (except for some species like phthalic acid, Ph). Oxalic (C2) acid was found as the most abundant species in summer, followed by Ph. Oxalic (C2) acid was also found as the most abundant species in winter, but followed by malonic (C3) acid. The C2 diacid comprised 28–66% of the total diacid concentrations. The diacids with higher carbon numbers were less abundant, although C9 diacid was relatively abundant (2%). Glyoxylic acid (ωC2) and methylglyoxal were found as the most abundant ketocarboxylic acid and dicarbonyl in both seasons, respectively. The concentrations of the total diacids, total ketoacids and total dicarbonyls ranged from 224 to 1381 ng m−3, 10 to 89 ng m−3 and 5 to 21 ng m−3, respectively. Their relative abundances in PM2.5 mass were 1.18%, 0.06% and 0.02%, respectively. High concentrations of toluene (winter: 33.8 μg m−3; summer: 41.3 μg m−3) and naphthalenes (winter: 1.2 μg m−3; summer: 1.9 μg m−3) observed were one possible source for the abundant phthalic and also methylmaleic acids detected.