LAUSR

Abstract In this study, the carbonaceous aerosols were separated into organic carbon (OC), water soluble OC (WSOC), water soluble humic-like substances (HULIS), water soluble non-HULIS, water insoluble OC (WINSOC), and soot carbon (SC). Then the abundance and 14C content of carbon fractions were determined to assess the contribution of contemporary versus fossil sources. The results showed that the OC fraction is the major carbon fraction, the OC sub-fractions such as WSOC, HULIS, non-HULIS, and WINSOC accounted for 39.5%–66.7%, 24.8%–43.2%, 11.9%–23.5%, and 31.3%–55.2% of total carbon (TC), respectively. The 14C data show that the contribution of contemporary carbon (fc) to TC is 38.3%–63.5%, all carbon fractions were mixtures of carbon derived from contemporary and fossil sources. The fc values of OC (38.8%–63.9%) more than that (25.7%–46.6%) of SC in the same sample, indicated OC generally contained more contemporary carbon than SC. The WSOC and HULIS had relatively higher fc levels than the corresponding WINSOC and the fc values of WINSOC all less than 45%, indicated that the insoluble organic fractions in PM2.5 samples were dominated by fossil fuel related sources. These results suggested that the contemporary and fossil contributions for different carbon fractions are different. In addition, the seasonal and spatial variations of contemporary and fossil contributions to carbon fractions indicated that the PM2.5 samples collected during summer at background site (Maofengshan, MFS) and winter at urban site (Wushan, WS) have relative high contribution from contemporary sources, suggested the differences of primary and secondary sources at the two sites.