The NASA Pacific Exploratory Mission-West experiment in 1991 and 1994 covered large portions of the western Pacific Ocean troposphere and transects of the troposphere of the equatorial and subtropical North Pacific Ocean. Sulfur dioxide and dimethyl sulfide were concurrently measured from the surface to 12 km. In 1991, sulfur dioxide had significant anthropogenic and volcanic sources. In 1994, sulfur dioxide aloft was significantly lower than in 1991. During both periods, deep convection was responsible for the distribution of sulfur dioxide and dimethyl sulfide. An assessment is made of the proportion of sulfur dioxide that could be made from dimethyl sulfide convected to high altitude. The subsequent formation of new aerosol particles from sulfur dioxide at high altitude is evaluated. ¿ 1997 American Geophysical Union