Direct measurements of dry and wet deposition of black carbon over the Southern Great Plains site

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Description

The atmospheric lifetime of black carbon (BC), an important light-absorbing aerosol species, is estimated to be 2-3 weeks and controlled by a combination of wet and dry deposition, which are poorly constrained by observations. Much work has focused on BC emission inventories, but the deposition component of the lifecycle remains unconstrained. Deposition of BC is grouped with other aerosols in global climate models, despite differences in climate impacts. We show that the single particle soot photometer is a viable instrument to measure refractory BC (rBC) surface-atmosphere exchange fluxes of refractory BC (rBC) particle mass and number by eddy covariance. We report field measurements of rBC dry and wet deposition rates during the summer of 2017 at the Southern Great Plains field site in Oklahoma. We estimate a dry deposition velocity of rBC mass (2.3±1.4 mm/s) and particle number (0.6±1.5 mm/s). We estimate a wet deposition flux that accounts for a wet deposition velocity of 6-10 mm/s over the 14 cm of rainfall observed during the campaign. Integrating total observed precipitation, we estimate that during the campaign, dry deposition constitutes 37% ± 7% of total deposition. Our data indicate a rBC mass lifetime of 6-11 days for dry deposition and 1-3 days for wet deposition during this campaign.