Photochemical production and loss of organic acids in high Arctic aerosols during long range transport and polar sunrise ozone depletion events
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Unique daily measurements of water-soluble organics in fine (< 2 μm) and coarse (>2 μm) aerosols were conducted at Alert in the Canadian Arctic in winter to spring of 1992.They yield insight into photochemical production and loss of organics during long-rangetransport and ozone depletion events following polar sunrise. Comprehensive analyses ofa,w-dicarboxylic acids (C2-C12), w-oxocarboxylic acids (C2-C9) and a-dicarbonyls (C2, C3) aswell as pyruvic acid and aromatic (phthalic) diacid were conducted using GC and GC/MStechniques. Oxalic (C2) acid was generally the dominant diacid species in both fine and coarsefractions, followed by malonic (C3) and succinic (C4) acids. Concentrations of total diacids inthe fine aerosol fraction (0.2-64 ngm-3) were 5-60 times higher than those in the coarsefraction (0.01-3 ngm-3). After polar sunrise in early March, the total concentration of fineaerosol diacids increased by a factor of 3 to 5 while the coarse mode did not changesignificantly. From dark winter to sunlit spring, temporal changes in correlations and ratios ofthese water-soluble organics to vanadium and sulfate measured simultaneously suggest thatatmospheric diacids and related organic compounds are largely controlled by long-rangeatmospheric transport of polluted air during winter, but they are significantly affected byphotochemical production. The latter can occur in sunlight either during transport to theArctic or during photochemical events associated with surface ozone depletion and brominechemistry near Alert in spring. Conversion of gaseous precursors to particulate matter viaphotochemical oxidation was intensified at polar sunrise, resulting in a peak in the ratio oftotal diacids to V. During ozone depletion events, complex patterns are indicated inphotochemical production and loss depending on the diacid compound. Unsaturated (maleicand phthalic) diacids were inversely correlated with particulate Br whereas saturated diacids(C2-C4) positively correlated with particulate Br. These results suggest that Br chemistryassociated with ozone depletion leads to degradation of unsaturated diacids and to theproduction of smaller saturated diacids.
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