Fast time resolution (>1 Hz) sulfur dioxide (SO2) measurements were obtained using an atmospheric pressure ionization mass spectrometer with isotopically labeled internal standard on the NASA Wallops P-3B during the NASA Transport and Chemical Evolution Over the Pacific (TRACE-P) field experiment. The high time resolution for SO2 allowed a view into the dynamics of SO2 transport, including the effects of clouds. Two missions along 124.5¿E from the vicinity of Taiwan to the northern Yellow Sea near the Korean peninsula were flown on consecutive days with quite different weather conditions. Although the winds on both flights were westerly to northwesterly, the SO2 concentrations were markedly different in vertical and horizontal distributions. Together with turbulence measurements and other high rate data on the P-3B, we have assessed how cloud processing and atmospheric dynamics may have caused the differences in the SO2 distributions. Below 2 km, SO2 layers of a few hundred meters depth were often isolated from the mixed layer. The relatively slow process of entrainment limited loss of SO2 to the marine mixed layer. When compared to 3-D model results of SO2 along the flight track, the in situ SO2 data showed that the model poorly represented the SO2 distribution along the flight track for the cloudy day, while the model gave a reasonably good representation of the in situ data during the clear air flight. On the clear air flight day, the model achieved a closer representation of the SO2 distribution, but it overestimated the SO2 concentrations just above the well-mixed boundary layer. The deviations between the observations and the model appear to be related the treatment of the boundary layer dynamics.