Source and reaction pathways of dicarboxylic acids, ketoacids and dicarbonyls in arctic aerosols: One year of observations

Normal saturated (C2---C11) and unsaturated (C4---C5, C8) dicarboxylic acids were measured in arctic aerosol samples collected weekly at Alert, Canada in 1987–1988. In all seasons, oxalic (C2) acid was usually the dominant diacid species (1.8−70 ng m−3, av. 14 ± 12 ng m−3) followed by malonic (C3; 0.05−19 ng m−3, av. 2.5 ± 3.3 ng m−3) and succinic (C4; 0.51−18 ng m−3, av. 3.8 ± 3.5 ng m−3) acids. The total concentrations of dicarboxylic acids showed a seasonal variation (4.3−97 ng m−3, av. 25 ± 20 ng m−3),with two maxima in September to October and in March to April. The autumn peak is characterized by high concentrations of oxalic acid and azelaic (C9) acids, which were probably caused by enhanced contributions from anthropogenic and biogenic sources, respectively, followed by photochemical reactions. This is consistent with higher concentrations of n-alkanes from terrestrial plant waxes and of soil-derived aluminum in the autumn aerosol samples. On the other hand, during “Arctic Sunrise” in March to April, oxalic, malonic and succinic acids as well as some other (C5---C6) diacids were 5 to 20 times more abundant than in the preceding dark winter months, suggesting that diacids are produced in situ by secondary photochemical oxidation of organic pollutants carried to the Arctic. ω-Oxocarboxylic acids (C2---C5, C9), pyruvic acid and α-dicarbonyls (methylglyoxal and glyoxal) were also detected in the arctic aerosols. Their concentration also showed spring maxima; however, they were observed a few weeks earlier than the spring peak of diacids. The ω-oxoacids are likely intermediates to the production of α,ω-dicarboxylic acids at the polar sunrise.