Summertime High Abundances of Succinic, Citric, and Glyoxylic Acids in Antarctic Aerosols: Implications to Secondary Organic Aerosol Formation

Observations of organic compounds associated with natural sources are scarce in Antarctica, which limits our understanding of their sources and formation processes over the pristine region. Summertime Antarctic PM10 samples collected from Bharati station were studied for a homologous series of dicarboxylic acids (C-2-C-12), omega-oxoacids (C-2-C-9), alpha-dicarbonyls (C-2-C-3) as well as citric and pyruvic acids by employing a water-extraction followed by dibutyl ester derivatization technique and analyzed using capillary gas chromatography (GC). Results show that succinic (C-4) and citric acids are the foremost abundant among the measured organic acids followed by glyoxylic (omega C-2), azelaic (C-9), and adipic (C-6) acids. Such a typical molecular distribution of organic acids suggests the dominance of natural sources over the Antarctic. Two distinct air masses arrived from different altitudes, high and low altitude-troposphere (HTAs and LTAs), showed a significant difference in mass concentrations of organic acids with higher values in LTAs. Total diacids-C accounted for similar to 9% of total carbon in HTAs, which is linked to chemical aging during long-range transport. The higher abundance of C-4 and citric acids are likely produced through secondary photooxidation of marine-derived organic precursors, such as unsaturated fatty acids, phenolic, and biogenic isoprene compounds enriched in sea-surface microlayer, via sea-to-air emission as confirmed by the significant (p < 0.05) correlations among the organic tracer compounds. Minor concentrations of oxalic and malonic (C-2 and C-3) acids were attributed to photo iron-complex reactions in the aqueous-phase atmosphere. These findings may help in reducing model uncertainties and present new insights into the secondary formation of organic aerosols in the polar environment.