A box model of DMS oxidation in the clean, low-NO, marine atmospheric boundary layer has been used to predict the latitude dependence of the aerosol methanesulfonate to non sea-salt sulfate ratio. The observed latitude dependence of this ratio in the Southern Hemisphere can be reproduced reasonably well if the full suite of reactions proposed by Yin ct al. (1990a) is employed, and a strong temperature dependence is specified in the rates of decomposition of CH3SO2 and CH3SO3 radicals.