Atmospheric pollutants over northwest Pacific Rim region (the East China Sea, the Yellow Sea, and the Sea of Japan) were observed from an airplane from October 5 to October 11, 1991, as one of the first intensive field studies of the International Global Atmospheric Chemistry/East Asian North Pacific Regional Experiment (IGAC/APARE). Ozone, NOx, Aerosols, SO2, hydrocarbons, CO, and aldehydes were measured. In this paper, the results of this experiment for ozone, NOx and SO2 measurements are described. Ozone and NOx were negatively correlated, which is contrary to the normal correlation observed in background areas. We believe that this is due to the large contribution of the upper atmosphere in most cases. The vertical distribution of SO2 concentrations indicates the impact of the Asian continental air mass. ¿ American Geophysical Union 1995