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Saturated (C 2 -C 11 ) and unsaturated (C 4 -C 5 , C 8 ) dicarboxylic acids were measured in arctic aerosol and surface snowpack samples collected during dark winter (February) and light spring (April-May) using a gas chromatography and gas chromatography/mass spectrometry. Their molecular distributions were characterized by a predominance of oxalic acid (C 2 ), except for few spring snowpack samples that showed the predominance of succinic acid (C 4 ). Concentrations of short chain saturated diacids (C 3 -C 5 ) and 4-ketopimelic acid in the aerosol samples increased by a factor of ~5 from winter to spring. In contrast, those of saturated C 6 -C 11 diacids and unsaturated (maleic, methylmaleic and phthalic) acids decreased by a factor of ~4 from winter to spring aerosol samples. Snowpack samples also showed a similar trend. These results of the aerosol samples suggested that the diacids are largely produced in spring by photochemical oxidation of hydrocarbons and other precursors that are transported long distances from the mid-and low-latitudes to the Arctic, but the production of oxalic acid is in part counteracted by photo-induced degradation possibly associated with bromine chemistry.

[1] Atmospheric particles were collected in the high Arctic at Alert during winter (February) and spring (April-May) and were subjected to stable carbon isotopic (d 13 C) measurements to better understand the source of carbonaceous aerosols. The mean d 13 C values of aerosol total carbon (TC) were observed to increase from winter (À25.7 ± 0.7%) to spring (À23.7 ± 0.8%). A strong correlation (r 2 = 0.92, p < 0.001) was found between the d 13 C values and Na + /TC ratios. The increased d 13 C values were most likely explained by an enhanced sea-to-air emission of marine organic matter to the high Arctic and also by a decreased atmospheric transport of anthropogenic carbon from the midlatitudes. The backward trajectory analysis together with inorganic ion analysis indicated that spring aerosols were more affected by the Arctic Ocean than winter aerosols that were mainly derived from the primary pollutants emitted in the midlatitudes. On the basis of the d 13 C values and Na + /TC ratios, contribution of marine organic matter to aerosol TC was estimated to be 45% in late spring. The enhanced sea-to-air emission of marine organic carbon is probably linked with a melting of sea ice, expansion of leads, and increased biological activity in the Arctic Ocean after the polar sunrise in spring.

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