We analyzed the suspended particle size distribution in the range of 0.5 to 10 µm and the optical properties of the particles from March 2007 to December 2010 at a site on the Loess Plateau (SACOL; 35.57°N, 104.08°E; 1965.8 m a.s.l.) about 48 km southeast of the center of Lanzhou. The results indicated that the variation in PM10 was much larger in spring than in winter because of frequent dust events or local blowing soil dust during spring. The highest number concentrations of coarse-mode particles were likely attributable to dust events that transported mineral dust or soil dust in the spring season, caused by cold fronts or strong local winds. In contrast, the fine-mode particles that dominated in the cold season at SACOL were probably indicative of anthropogenic sources related to fossil-fuel combustion and biomass burning. The comparison of dust events and anthropogenic air pollution shows a clear distinction of lower PM10 with higher Bap for pollution episodes and higher PM10 with lower Bap for dust events. These findings suggest that the results in the cold season were likely attributable to light absorption of black carbon, and the coarse mode particles were dominant during dust events in spring.