Abstract
High volume aerosol samples were collected continuously at Mawson, Antarctica (67°36'S, 62°30'E), from February 1987 through October 1989. All samples were analyzed for Na+, Cl-, SO4 =, NO3 -, methanesulfonate (MSA), NH4 +,7Be, and210Pb. The annual mean concentrations of many of the species are very low, substantially lower than even those over the relatively pristine regions of the tropical and subtropical South Pacific. The concentrations at Mawson are comparable both in magnitude and in seasonality to those which have been measured in long term studies at the South Pole and at the coastal German Antarctic research station, Georg von Neumayer (GvN). This comparability suggests that the aerosol composition may be relatively uniform over a broad sector of the Antarctic. The concentrations of most of the species exhibit very strong and sharply-defined seasonal cycles. MSA, non-sea-salt (nss) SO4 = and NH4 + all exhibit similar cycles, with maxima during the austral summer (December through February) being more than an order of magnitude higher than the winter minima. The limited7Be data appears to exhibit a similar cycle. Although nitrate and210Pb also exhibit relatively high concentrations during the austral summer, their cycles are far more complex than those of the previous species with indications of multiple peaks. As expected, the concentration of sea-salt (as indicated by Na+ and Cl-) peaks during the winter. The results from multiple variable regression analyses indicate that the dominant source of nss SO4 = is the oxidation of dimethylsulfide (DMS) which produces MSA and nss SO4 = in a ratio of about 0.31 (about five times higher than that over the tropical and subtropical oceans). However, a very significant fraction (about 25%) of the nss SO4 = is associated with NO3 -, The seasonal cycle of NO3 - is similar to that of210Pb and distinctly different from that of7Be and MSA. These results indicate that the major source of NO3 - over Antarctica is probably continental as opposed to stratospheric or marine biogenic.
Highlights
Despite the importance of nitrogen and sulfur species to numerous areas of the atmospheric sciences, many aspects of the atmospheric sulfur and nitrogen cycles are still poorly understood
Our results when combined with previously published data indicate that the aerosol composition is very uniform over a broad sector of Antarctica and the southern oceans
The biogenic sulfur component appears to be uniform over a region of the southern ocean that covers perhaps as much as 25-30% of the earth's surface
Summary
Despite the importance of nitrogen and sulfur species to numerous areas of the atmospheric sciences, many aspects of the atmospheric sulfur and nitrogen cycles are still poorly understood. We have been collecting bulk aerosol samples at Mawson, Antarctica, since February 1987 These samples are analyzed to determine the atmospheric concentrations of: 1) sodium from which the sea-salt concentrations are calculated; 2) non-sea-salt (nss) SOn = which is produced from the oxidation of SO2 that is derived primarily from anthropogenic combustion sources, from volcanoes and from the oxidation of reduced organic sulfur gases emitted from the ocean; 3) MSA (methanesulfonate), an atmospheric oxidation product of DMS (dimethyl sulfide) which is produced by biological sources in the ocean; 4) NO3-, derived from the oxidation of NO and related species that are produced by anthropogenic combustion sources (including biomass burning) and from natural sources - principally soil emissions, lightning, and stratospheric processes; 5) NH4 +, derived from continental and oceanic sources; 6) 7Be, (half-life = 53.6 d) a tracer for transport from the stratosphere and upper troposphere where it is produced from the spallation of nitrogen by cosmic rays; 7) 21°pb, a tracer for air masses that have recently been in convective contact with continental land masses since it is a decay product of 222Rn (half-life = 3.8 d) for which the overwhelmingly dominant source is emission from soils
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