Latitudinal distributions of atmospheric MSA and MSA/nss-SO ₄^2- ratios in summer over the high latitude regions of the Southern and Northern Hemispheres

To characterize the spatial distributions of methane-sulfonic acid (MSA) as represented by measured aerosol methane sulfonate (MS) and its relationships with non-sea-salt (nss) sulfate (SO₄^2-) in the marine atmospheric boundary layer over high-latitude regions, bulk aerosol samples were collected during eight cruises during the Chinese National Antarctic and Arctic Research Expeditions from 1998 to 2008. The concentrations of MSA (an indicator of marine biogenic sulfur production), sulfate, sodium and chloride in samples were analyzed using ion chromatography. Increases in the aerosol MSA concentrations and MSA/nss-SO₄^2- ratios were observed as functions of latitudes in the Pacific Ocean, more abruptly near high southern latitudes as compared to those in high northern latitudes. The MSA concentrations increased from 0.011 g m^-3 near the equator to 0.26 g m^-3 at 63S, 23W and from 0.0013 g m^-3 at northern midlatitudes to 0.19 g m^-3 at 58N, 175E. However, MSA decreased in the latitudes north of 58N in the Pacific, where air temperature was lower. MSA/nss-SO₄^2- ratios increased from 0.024 near the equator to 0.93 at 62S, 4E and from 0.0031 around northern midlatitudes to 0.39 at 68N, 169W. The MSA concentrations were more correlated with MSA/nss-SO ₄^2- (R² = 0.43, n = 60) in Southern Hemisphere than Northern Hemisphere (R² = 0.091, n = 40). No significant correlation was found between MSA/nss-SO₄^2- and air temperature at high latitudes, indicating latitudinal temperature variations were not a main factor responsible for the MSA/nss-SO₄^2- variation in those regions. Substantial increases in the concentrations of MSA in coastal Antarctica may indicate additional sources of biogenic S besides the emissions of dimethylsulfide from the sea.