The data used in this work are size‐segregated aerosols collected from three ambient‐source sites with few interferences from nearby activities from fall into winter time in 1992. The analysis of the aerosol species is used to apportion source contributions to the aerosols sampled at Yen‐Ping elementary school situated in the Taipei metropolitan area. Concentration ratios of characteristic species to mass of near‐source aerosols are selected to represent source features. Source apportionment of water‐soluble ions with sea‐origin at Yen‐Ping site is calculated from the “chlorine loss” process. The inference on the compound forms of sulfates shows that (NH4)2SO4prevailing in the sub‐micron mode, whereas the sulfates from sea‐origin are undoubtedly dominant in the coarse mode. Estimate on source contributions for PM10aerosols at Yen‐Ping site shows that around 51% came from transportation activities, 23% from sea‐spray process, 17 to 19% from construction work, and 15% from the secondary chemical reaction. The procedure of this work overestimates source contributions by 6 to 8%.