Methanesulfonate and non-sea-salt sulfate concentrations in aerosols at Syowa, Antarctica

Aerosol samples were collected at Syowa, Antarctica (69 degrees 00'S, 39 de grees 35'E), from February 13, 1993 to January 29, 1994. All samples were a nalyzed by ion-chromatography to examine the mass concentrations of sodium (Na+), sulfate (SO42-), and methanesulfonate (MSA or CH3SO3-). The concentr ations of MSA ranged from a mean value of 1.4 ng m(-3) during the winter (f rom June to August 1993) to 32 ng m(-3) during the summer (from February to March 1993, and from December 1993 to January 1994). The mean concentratio n of non-sea-salt sulfate (nss-SO42-) was 34 ng m(-3) during the winter, wh ereas during the summer it was 147 ng m(-3). The mean molar ratio of MSA to nss-SO42- was 0.25 during the summer, but values during the winter decreas ed to 0.04. This resulted from the difference in amplitudes between the sea sonal variations of MSA and nss-SO42- concentrations. A similar variation w as also found at other sampling sites over a broad area of the southern oce ans. Since the interaction between the atmospheric boundary layer and the f ree troposphere seems to regionally vary, it is difficult to explain the se asonal variation of the MSA/nss-SO42- 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.