Particulate matter emission mechanisms from biochar-amended soils: A potential contaminant transport pathway

Abstract:

Carbon sequestration strategies such as large-scale biochar application may provide sustainable pathways to increase the terrestrial storage of carbon in soils. Applied biochar is expected to last in the soil for hundreds of years, thereby mitigating climate change impacts and slowing down land degradation. However, recent studies have shown that the applied biochar may also leave the application areas either by wind or water transport, thereby lowering their intended effect on improving soil or water quality. Yet, the mechanism of biochar emission by wind is poorly understood. Using wind tunnel experiments to simulate different wind regimes, we quantified particulate emission from sand amended with 1 - 5 % (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 PM₁₀ emission by up to 400% due to the direct resuspension of fine biochar particles. At wind speeds above the threshold speed, emission increased by up to 300% even from biochar without fine fractions due to collisions and abrasion by fast-moving sand particles. We used a theoretical framework to explain the disproportionally higher biochar emission than the emission of natural soil particles even at wind speeds below the threshold wind speed for background soil. This result indicates that current emission models may underestimate the biochar emission potential from amended soils. As fine biochar particles effectively sorb contaminants from the soil, the preferential emission of fine biochar particles by wind may lead to concentration of contaminants in the airborne dust. Our results will help assess the wind-driven biochar emission from amended soils and its impact on public health risks.