Atmospheric aerosol particles resulting from the oxidation of dimethylsulfide (DMS) may have an impact on global climate if they result in an enhancement in the cloud condensation nuclei (CCN) number concentration and shortwave cloud albedo. To characterize and quantify relationships within the DMS/CCN/climate system, simultaneous measurements were made over the northeastern Pacific Ocean in April and May 1991 of particulate non-sea-salt sulfate, methanesulfonate, and ammonium mass size distributions, number size distributions of particles having diameters between 0.02 and 9.6 μm, CCN concentrations at 0.3% supersaturation, relative humidity, and temperature. Comparisons between particle mass and surface area indicate that non-sea-salt sulfate, methanesulfonate, and ammonium were not involved in new particle production on the 12- to 24-hour time scale of the measurements. Instead, high levels of available particulate surface area resulted in the condensation of the gas phase precursors onto existing aerosol. A doubling of non-sea-salt sulfate, methanesulfonate, and ammonium mass correspond to a 40 to 50% increase in number in the accumulation mode size range. Likewise, a doubling of the non-sea-salt sulfate mass corresponded to a 40% increase in the CCN number concentration. As methanesulfonate made up a very small fraction of the soluble particulate mass, no correlations were found between methanesulfonate mass and CCN number. In a separate experiment, measurements were made of particulate non-sea-salt sulfate, methanesulfonate, and ammonium mass size distributions over the central Pacific Ocean during February 1991. The percent of methanesulfonate in the supermicrometer particle size fraction was greater in these samples than in those collected over coastal waters of the northeastern Pacific. In both regions the non-sea-salt sulfate mass size distributions were bimodal, while ammonium was found to be concentrated in larger accumulation mode particles. ¿ American Geophysical Union 1993