Multi-Satellite Assessment of Factors Controlling Biomass Burning Aerosol Formation over the South China Sea

This study presents a novel, satellite-based framework for quantifying the relative contribution of regional transport in biomass burning aerosol (BBA) formation over the South China Sea (SCS). We integrate the biomass burning emission (BBE) rates from potential source regions with a random forest regression model, which is driven by backward trajectory analysis. This approach isolates and evaluates the relative contribution from transported sources. The model demonstrates robust predictive skill for BBA concentrations (R2 = 0.78 on an independent test set), using only transport-weighted BBE rates and meteorological data as inputs. Quantitative interpretation via SHAP (Shapley Additive exPlanations) analysis reveals nonlinear relationships and the distinct importance of transport-source features. A key finding is that BBE originating from northern Laos and Thailand contributes 21.23% to the predicted BBA concentrations over the SCS. Furthermore, there is a clear nonlinear positive correlation between the regional BBE rates and downwind BBA concentration, except for transport from Cambodia. Our results pinpoint that the impact of regional transport is paramount, governed by a combination of source emission intensity, transport duration, and trajectory pathway. This study establishes a satellite-driven methodology for attributing aerosol sources and clarifies the dominant controls on BBA concentration variability in a major maritime receptor region.