Methanesulfonate and Non-Sea-Salt Sulfate Concentrations in Aerosols at Syowa, Antarctica

Abstract

Aerosol samples were collected at Syowa, Antarctica (69°00'S, 39°35'E), from February 13, 1993 to January 29, 1994. All samples were analyzed by ion-chromatography to examine the mass concentrations of sodium (Na⁺), sulfate (SO₄^2-), and methanesulfonate (MSA or CH₃SO₃^-). The concentrations of MSA ranged from a mean value of 1.4ng m^-3 during the winter (from June to August 1993) to 32ng m^-3 during the summer (from February to March 1993, and from December 1993 to January 1994). The mean concentration of non-sea-salt sulfate (nss-SO₄^2-) was 34ng m^-3 during the winter, whereas during the summer it was 147ng m^-3. The mean molar ratio of MSA to nss-SO₄^2- was 0.25 during the summer, but values during the winter decreased to 0.04. This resulted from the difference in amplitudes between the seasonal variations of MSA and nss-SO₄^2- concentrations. A similar variation was also found at other sampling sites over a broad area of the southern oceans. Since the interaction between the atmospheric boundary layer and the free troposphere seems to regionally vary, it is difficult to explain the seasonal variation of the MSA/nss-SO₄^2- molar ratio by only the transport of air parcels from the free atmosphere. The seasonal variation of MSA/nss-SO₄^2- molar ratio appears to be mainly the result of the seasonal variation of the dimethylsulfide (DMS of CH₃SCH₃) oxidation process.