Sources of black carbon in aerosols: fossil fuel burning vs. biomass burning

The uncertainty in black carbon (BC) analysis and our inability to directly quantify the BC sources in the atmosphere has led to the uncertainty in compiling a regional or global BC emission inventory attributed to biomass burnings. We initiate this study to demonstrate a new approach, which quantifies the source of BC in the atmosphere between biomass and fossil fuel burnings. We applied the newly developed multi-element scanning thermal analysis (MESTA) technology to quantify BC and organic carbon (OC), respectively, in aerosol samples. MESTA can also separate BC from OC for subsequent radiocarbon analyses. Because fossil fuel has been depleted of radiocarbon and biomass has radiocarbon of the modern atmospheric level, we can quantify the sources of BC between fossil fuel and biomass burnings. We sampled the PM2.5 in the ambient air of central Tallahassee and its rural areas during the May-June (prescribed burning) and Nov-Dec (non-burning) periods. The results indicate that biomass burning contributed 89×1% and 67×2% of BC, respectively, during May-June and Nov.-Dec. periods. The rest of PM2.5 BC was contributed from fossil fuel burning. The radiocarbon contents of the OC was 103.42×0.55 percent modern carbon (pmC), which is consistent with the current atmospheric level with a trace of the bomb radiocarbon remained from the open atmosphere nuclear testing.