Nitrogen and sulfur species in acrosols at Mawson,Antarctica, and their relationship to natural radionuclides

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.