TRANSPORT OF SULFUR-DIOXIDE FROM THE ASIAN-PACIFIC RIM TO THE NORTH PACIFIC TROPOSPHERE

The NASA Pacific Exploratory Mission over the Western Pacific Ocean (P EM-West B) field experiment provided an opportunity to study sulfur di oxide (SO2) in the troposphere over the western Pacific Ocean from the tropics to 60 degrees N during February-March 1993. The large suite o f chemical and physical measurements yielded a complex matrix in which to understand the distribution of sulfur dioxide over the western Pac ific region, In contrast to the late summer period of Pacific Explorat ory Mission-West A (PEM-West A) (1991) over this same area SO, showed little increase with altitude, and concentrations were much lower in t he free troposphere than during the PEM-West B period. Volcanic impact s on the upper troposphere were again found as a result of deep convec tion in the tropics. Extensive emission of SO, from the Pacific Rim la nd masses were primarily observed in the lower well-mixed part of the boundary layer but also in the upper part of the boundary layer. Analy ses of the SO, data with aerosol sulfate, beryllium-7, and lead-210 in dicated that SO2 contributed to half or more of the observed total oxi dized sulfur (SO, plus aerosol sulfate) in free tropospheric air, The combined data set suggests that SO2 above 8.5 km is transported from t he surface but with aerosol sulfate being removed more effectively tha n SO2. Cloud processing and rain appeared to be responsible for lower SO, levels between 3 and 8.5 km than above or below this region.