Abstract Compound‐specific stable carbon isotope ratios (δ 13 C) were measured for low molecular weight aliphatic (C 2 –C 6 ) dicarboxylic acids, phthalic acid, glyoxylic acid and glyoxal in Arctic aerosols collected at Alert (82.5°N) in late winter to early summer. Between dark winter in late February/early March to completely sunlit conditions in May the δ 13 C of many organic acids increased: (a) oxalic acid (C 2 ) from −23‰ to −5‰, (b) malonic acid (C 3 , a precursor of C 2 ) from −28‰ to −17‰, and (c) glyoxylic acid (ωC 2 , −18‰ to −10‰), also a precursor of C 2 . In contrast, glyoxal, another precursor of oxalic acid and succinic acid, showed a wide variation from dark to light and no clear seasonal trend. Concentrations of C 2 , ωC 2 and C 3 declined when their δ 13 C increased in April to May. The enrichment of 13 C occurred during the preferential breaking of 12 C– 12 C over 12 C– 13 C bond in oxalic and other acids as solar radiation increased during polar sunrise. Photochemically driven variations in the isotopic enrichment of 13 C of C 2 and related compounds that are a minor fraction of aerosol total carbon (TC), nevertheless they are the main source of variation in the δ 13 C values of TC during polar sunrise in the Arctic because the weakness of 12 C– 12 C bond compared to 12 C– 13 C bond is more pronounced for carboxylic acids than other species contributing to TC. This study on 13 C signature of these species allows to gain information on their poorly known atmospheric budget in spite of the fact that they are ubiquitous in the atmosphere.
Kawamura et al. (Sat,) studied this question.