Radiocarbon-Based Source Apportionment of Carbonaceous Aerosols at a Regional Background Site on Hainan Island, South China

To assign fossil and nonfossil contributions to carbonaceous particles, radiocarbon (C-14) measurements were performed on organic carbon (OC), elemental carbon (EC), and water-insoluble OC (WINSOC) of aerosol samples from a regional background site in South China under different seasonal conditions. The average contributions of fossil sources to EC, OC and WINSOC were 38 +/- 11%, 19 +/- 10%, and 17 +/- 10%, respectively, indicating generally a dominance of nonfossil emissions. A higher contribution from fossil sources to EC (similar to 51%) and OC (similar to 30%) was observed for air-masses transported from Southeast China in fall, associated with large fossil-fuel combustion and vehicle emissions in highly urbanized regions of China. In contrast, an increase of the nonfossil contribution by 5-10% was observed during the periods with enhanced open biomass-burning activities in Southeast Asia or Southeast China. A modified EC tracer method was used to estimate the secondary organic carbon from fossil emissions by determining C-14-derived fossil WINSOC and fossil EC. This approach indicates a dominating secondary component (70 +/- 7%) of fossil OC. Furthermore, contributions of biogenic and biomass-burning emissions to contemporary OC were estimated to be 56 +/- 16% and 44 +/- 14%, respectively.