Samples of fine particulate matter (PM2.5) were collected during July 2009 to March 2010 at a regional background site in East China. The mass concentrations of organic carbon (OC) and elemental carbon (EC) were characterized by the highest levels in winter (December to February) and the lowest abundances in summer (June to August). Conversely, the concentrations of levoglucosan were higher in summer than in winter. The observations were associated to the anthropogenic air pollutions (predominantly fossil-fuel combustions) transport from the center and north China with the northwest winds in winter and large contribution of the open biomass burning activities in South China and East China in summer, which was evident by air-mass trajectories and MODIS satellite fire counts. To assign fossil and nonfossil contributions of carbonaceous matters, the radiocarbon contents in water-insoluble OC (WINSOC) and EC in 4 combined samples representing four seasons were analyzed using the isolation system established in China. The results indicated that biomass burning and biogenic sources (59%) were the major contribution to the WINSOC, whereas fossil fuel (78%) was the dominant contributor to the refractory EC at this site. The source variation obtained by radiocarbon was consistent with other indicators, such as the OC/EC ratios and the levoglucosan concentration. Biomass burning and biogenic emissions were found to predominate in the summer and autumn, whereas fossil fuel emissions predominate in winter and spring.