Asian dust storm (ADS) not only increase the coarse particle concentrations, but also bring the fine and ultrafine particles to Taiwan. In this study, A PCA model was applied to identify the potential source categories, obtained through measuring ambient 10–500 nm particle number concentrations, size distributions and composition data, during an ADS and non-dust periods. The three factors estimated with rotational components during an ADS were vehicular emissions (52%), dust storm (24%), and primarily gasoline vehicles (12%). During non-dust periods, the three factors were vehicular emissions, secondary sulfate and nitrate (40%), combustion processes and traffic-related emissions (29%), and road dust (25%). In addition, vehicular emissions and road dust were the main sources (78%) during particulate matter episodes. The results showed that, along with wind direction and wind speed, PM composition and size distribution can be used to determine the locally dominant source categories, and to identify ADS episodes.