Generation, Resuspension, and Transport of Particulate Matter From Biochar-Amended Soils: A Potential Health Risk.

Large-scale soil application of biochar is one of the terrestrial carbon sequestration strategies for future climate change mitigation pathways, which can also help remove and sequester pollutants from contaminated soil and water. However, black carbon emissions from biochar-amended soils can deteriorate air quality and affect human health, as the biochar particles often contain a higher amount of sorbed toxic pollutants than the soil. Yet, the extent and mechanism of inhalable particulate matter (PM) emission from biochar-amended soils at different wind regimes have not been evaluated. Using wind tunnel experiments to simulate different wind regimes, we quantified particulate emission from sand amended with 1-4% (by weight) biochar at two size fractions: with and without <2-mm biochar. At wind speeds below the threshold speed for soil erosion, biochar application significantly increased PM emission by up to 400% due to the direct resuspension of inhalable biochar particles. At wind speeds above the threshold speed, emission increased by up to 300% even from biochar without inhalable fractions due to collisions of fast-moving sand particles with large biochar particles. Using a theoretical framework, we show that particulate matter emissions from biochar-amended soils could be higher than that previously expected at wind speeds below the erosion threshold wind speed for background soil. Our results indicate that current models for fugitive dust emissions may underestimate the particulate matter emission potential of biochar-amended soils and will help improve the assessment of biochar emission from amended soils.