Abstract
Abstract. 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 (C2) followed by malonic (C3) and/or succinic (C4) 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 α-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 α-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 C2 was found in two samples in which C4 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 C2 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 (δ13C) of bulk aerosol carbon and individual diacids. The δ13C of bulk aerosols showed −26.5‰ (range: −29.7 to −24.7‰, suggesting that marine aerosol carbon is derived from both terrestrial and marine organic materials. In contrast, oxalic acid showed much larger δ13C values (average: −20.9‰, range: −24.7‰ to −17.0‰) than those of bulk aerosol carbon. Interestingly, δ13C values of oxalic acid were higher than C3 (av. −26.6‰) and C4 (−25.8‰) diacids, suggesting that oxalic acid is enriched with 13C due to its photochemical processing (aging) in the marine atmosphere.
Highlights
In the Arctic Ocean summer aerosols, we detected a series of water-soluble dicarboxylic acids, ketocarboxylic acids and α-dicarbonyls
This study suggests the Arctic marine organic aerosols are influenced by sea-to-air emissions of marine organic materials and long-range transport of continental aerosols and their precursors, followed by photochemical processing in the atmosphere
We found a depletion of oxalic acid in the marine aerosols under foggy and cloudy conditions, which is possibly interpreted by selective degradation of oxalate-Fe complex in aqueous phase
Summary
Low molecular weight dicarboxylic acids are one of the most abundant organic compound classes in atmospheric aerosols They were reported in the urban (Kawamura and Ikushima, 1993; Sempéré and Kawamura, 1994; Rohrl and Lammel, 2001; Wang et al, 2002; Yao et al, 2002; Rompp et al., 2006; Kitanovski et al, 2011), mountainous (Legrand et al., 2007), marine (Kawamura and Sakaguchi, 1999; Mochida et al, 2003a, b), and Arctic and Antarctic atmospheres (Kawamura et al, 1996a, b, 2005; Narukawa et al, 2002, 2003). We report for the first time the molecular compositions of dicarboxylic acids and related compounds and their stable carbon isotopic compositions in the Arctic Ocean aerosols and discuss their sources and formation processes in the High Arctic marine atmosphere. TC and TN contents reported here were corrected for the field blank. δ 13 C and δ 15 N values were corrected to the field blank using isotopic mass balance equation
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