Determination of malic acid and other C-4 dicarboxylic acids in atmospheric aerosol samples

An ion chromatographic method was developed which is able to separate five unsubstituted and hydroxy C-4 dicarboxylic acids, succinic, malic, tartaric, maleic and fumaric acid, besides the other unsubstituted C-2-C-5 dicarboxylic acids, oxalic, malonic and glutaric acids, as well as inorganic ions in samples extracted from atmospheric particulate matter. By the application of this method it was found for both rural and urban sites and for various types of air masses that in the summer-time malic acid is the most prominent C-4 diacid (64 ng m(-3) by average), exceeding succinic acid concentration (28 ng m(-1) by average) considerably. In winter-time considerably less, a factor of 4-15, C-4 acids occurred and succinic acid was more concentrated than malic acid. Tartaric, fumaric and maleic acids were less concentrated (5.1, 5.0 and 4.5 ng m(-1) by average, respectively). Tartaric acid was observed for the first time in ambient air. The results indicate that in particular anthropogenic sources are important for the precursors of succinic, maleic and fumaric acids. Biogenic sources seem to influence the occurrence of malic acid significantly. (C) 2002 Elsevier Science Ltd. All rights reserved.