Kawamura K., Ono K., Tachibana E., Charriere B., Sempéré Richard. (2012). Distributions of low molecular weight dicarboxylic acids, ketoacids and alpha-dicarbonyls in the marine aerosols collected over the Arctic Ocean during late summer. Biogeosciences, 9 (11), p. 4725-4737. ISSN 1726-4170.
Titre du document
Distributions of low molecular weight dicarboxylic acids, ketoacids and alpha-dicarbonyls in the marine aerosols collected over the Arctic Ocean during late summer
Kawamura K., Ono K., Tachibana E., Charriere B., Sempéré Richard
Source
Biogeosciences, 2012,
9 (11), p. 4725-4737 ISSN 1726-4170
Oxalic and other small dicarboxylic acids have been reported as important water-soluble organic constituents of atmospheric aerosols from different environments. Their molecular distributions are generally characterized by the predominance of oxalic acid (C-2) followed by malonic (C-3) and/or succinic (C-4) acids. In this study, we collected marine aerosols from the Arctic Ocean during late summer in 2009 when sea ice was retreating. The marine aerosols were analyzed for the molecular distributions of dicarboxylic acids as well as ketocarboxylic acids and alpha-dicarbonyls to better understand the source of water-soluble organics and their photochemical processes in the high Arctic marine atmosphere. We found that diacids are more abundant than ketoacids and alpha-dicarbonyls, but their concentrations are generally low (< 30 ng m(-3)), except for one sample (up to 70 ng m(-3)) that was collected near the mouth of Mackenzie River during clear sky condition. Although the molecular compositions of diacids are in general characterized by the predominance of oxalic acid, a depletion of C-2 was found in two samples in which C-4 became the most abundant. Similar depletion of oxalic acid has previously been reported in the Arctic aerosols collected at Alert after polar sunrise and in the summer aerosols from the coast of Antarctica. Because the marine aerosols that showed a depletion of C-2 were collected under the overcast and/or foggy conditions, we suggest that a photochemical decomposition of oxalic acid may have occurred in aqueous phase of aerosols over the Arctic Ocean via the photo dissociation of oxalate-Fe (III) complex. We also determined stable carbon isotopic compositions (delta C-13) of bulk aerosol carbon and individual diacids. The delta C-13 of bulk aerosols showed -26.5 parts per thousand (range: -29.7 to -24.7 parts per thousand), suggesting that marine aerosol carbon is derived from both terrestrial and marine organic materials. In contrast, oxalic acid showed much larger delta C-13 values (average: -20.9 parts per thousand, range: -24.7 parts per thousand to -17.0 parts per thousand) than those of bulk aerosol carbon. Interestingly, delta C-13 values of oxalic acid were higher than C-3 (av. -26.6 parts per thousand) and C-4 (-25.8 parts per thousand) diacids, suggesting that oxalic acid is enriched with C-13 due to its photochemical processing (aging) in the marine atmosphere.
