Longer Lifetime of BC from Fossil Fuel Combustion than from Biomass Burning: Δ14C Evidence

Abstract

Black carbon (BC) significantly contributes to atmospheric warming and glacier melting. However, the atmospheric lifetime of BC from different fuel sources remains poorly constrained. By analyzing Δ14C of BC in PM2.5 and precipitation samples collected for three years at a remote site in the Tibetan Plateau, we found that BC from fossil fuel contribution (ffossil BC) in PM2.5 exhibited greater seasonal variation than those from South Asia and emission inventories. Precipitation-induced fractionation between fossil fuel combustion-derived BC (BCff) and biomass burning-derived BC (BCbb) resulted in an increase of ffossil BC to 68 ± 7% during the wet monsoon season, which is significantly higher than levels measured at a background site in South Asia and in simultaneously collected precipitation samples. Our findings provide direct evidence that the lifetime of BCff is longer than that of BCbb during the monsoon season. These results emphasize the increased climate forcing of BCff relative to BCbb at remote sites receiving long-range transported BC.