Measurements of the ambient concentrations of O3, NOx (NO+NO2), and PAN (peroxyacetyl nitrate) were collected at Kenting, a rural site near the southern end of Taiwan, during the autumn of 1991 as part of the Pacific Exploratory Mission-West A (PEM-West A) experiment. Two principal component analyses (PCAs) were performed on the data. The results of the PCA indicated that at least three different air mass types were observed at the site, including marine boundary layer, urban plume, and continental outflow (from the Asian mainland). The average concentrations determined for PAN and O3 in the marine boundary layer are 0.03¿0.02 and 13¿5 parts per billion by volume (ppbv), respectively. In the continental outflow type air masses the average concenrations of PAN and O3 were 0.33¿0.41 and 46¿7 ppbv, respectively. The data collected indicate that a minimum of 100--150 parts per trillion by volume (pptv) PAN is required in order to affect the production of ozone in the marine boundary layer. ¿ American Geophysical Union 1996