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

Normal saturated (C-2-C-11) and unsaturated (C-4-C-5, C-8) dicarboxylic acids were measured in arctic aerosol samples collected weekly at Alert, Canada in 1987-1988. In all seasons, oxalic (C-2) acid was usually the dominant diacid species (1.8-70 ng m(-3), av. 14 +/- 12 ng m(-3)) followed by malonic (C-3; 0.05-19 ng m(-3), av. 2.5 +/- 3.3 ng m(-3)) and succinic (C-4; 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 (C-9) 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 (C-5-C-6) diacids were 5 to 20 times more abundant than in the preceding dark winter months, suggesting that diacids are produced ill situ by secondary photochemical oxidation of organic pollutants carried to the Arctic. omega-Oxocarboxylic acids (C-2-C-5, C-9), pyruvic acid and alpha-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 omega-oxoacids are likely intermediates to the production of alpha,omega-dicarboxylic acids at the polar sunrise.