VARIATIONS IN THE METHANESULFONATE TO SULFATE MOLAR RATIO IN SUBMICROMETER MARINE AEROSOL-PARTICLES OVER THE SOUTH-PACIFIC OCEAN

Seawater concentrations of dimethylsulfide (DMS) and atmospheric concentrations of DMS, sulfur dioxide, methanesulfonate (MSA), and non-sea-salt (nss) sulfate were measured over the eastern Pacific Ocean between 105-degrees and 110-degrees-W from 20-degrees-N to 60-degrees-S during February and March 1989. Although the samples collected in the southern hemisphere appear to be of marine origin, no significant correlation was found between the latitudinal distributions of DMS, SO2, MSA, and nss SO4=. However, an inverse correlation (r2 = 0.87) was found between atmospheric temperature and the MSA to nss SO4= molar ratio in submicrometer aerosol particles with a decrease in temperature corresponding to an increase in the molar ratio. Although this trend is consistent with laboratory results indicating the favored production of MSA at lower temperatures, it is contrary to southern hemisphere baseline station data. This suggests either a decrease in the supply of DMS relative to nonmarine sources of nss SO4= at the baseline stations in winter or additional mechanisms that affect the relative production of MSA and nss SO4=.