First observation of biochar aerosol generation from raindrop impact on biochar-amended soils

This study presents the first experimental evidence of biochar (BC) aerosol generation via raindrop impact on amended soils, combining controlled rainfall simulations with year-long field monitoring of atmospheric particulates from a BC-treated plot (2.0 wt%). Microscopic and isotopic analyses confirmed BC incorporation in total suspended particles (TSP), accounting for 15.8-26.5 wt% of TSP mass. BC aerosol levels peaked at ∼47 mm/24 h (heavy rain classification) before decreasing at extreme precipitation rates. BC incorporation significantly increased TSP's organic/elemental carbon contents and altered trace metal profiles, mirroring the soil-applied wood BC composition. Electron paramagnetic resonance revealed elevated environmentally persistent free radical (EPFR) concentrations in BC-containing TSP (from 3.26 × 10¹⁷-7.81 × 10¹⁷ spins/g), which exhibited prolonged average half-lives (t_1/e) (68.4 vs 51.6 days in the control) and a positive correlation with BC mass fraction. The BC-derived EPFRs also significantly boosted the oxidative potential (reflected by dithiothreitol activity) of TSP. These results demonstrate an unrecognized atmospheric BC emission pathway with implications for carbon cycling and air quality, necessitating optimized BC production and soil application protocols to balance agricultural benefits with aerosol mitigation.