Inventory Uncertainty and Transboundary Transport of Biomass-Burning Black Carbon in Southern China: Insights from...

Black carbon (BC) from biomass burning (BCbb) constitutes a major fraction of global BC's climate impact. Yet, the contribution of BCbb to atmospheric BC concentrations estimated by emission inventory-based models remains highly uncertain due to the lack of source-diagnostic observational constraints. Here, we present year-round, 14C-based measurements of BCbb from two regional and one background site in southern China. By comparing these measurements with tailored simulations from an atmospheric transport model, we find that although the model reproduces the seasonal variation reasonably well, simulated BCbb remains subject to considerable uncertainty (NMB: -68% to +28%). Unmonitored biomass burning (BB) in mainland China can result in a substantial model-observation discrepancy. Our results reveal that residential BB across East Asia is the main contributor to BCbb in southern China. Transport of BCbb from Southeast Asia is also important in summer. Notably, transboundary BB pollution from Southeast Asia, facilitated by free-tropospheric transport, cannot be ignored even in winter, when continental air masses prevail. Our findings highlight that the transboundary contribution of BCbb may exceed prior estimates. These results underscore the need to update emission inventories by incorporating overlooked BB sources.