Observational constraints on wet and dry deposition of black carbon

Black carbon (BC) is one form of light-absorbing aerosol that impacts atmospheric temperature, cloud formation and properties, the albedo of snow and ice surfaces, and the timing of snowmelt. The magnitude of these impacts is dictated by the atmospheric lifetime of BC,which are controlled by wet and dry deposition. Parameterization of BC deposition and dry deposition in particular, is limited due to the lack of available instrumentation to measure this process, and thus the lack of observational datasets with which to evaluate existing models.

We show that the single particle soot photometer (SP2), an aerosol instrument that quantifies individual aerosol optical size and BC mass content, can measure surface-atmosphere exchange fluxes of refractory BC (rBC) particle mass and number by eddy covariance. We present SP2 field measurements of rBC dry and wet deposition rates obtained during summer 2017 at the Southern Great Plains site in Oklahoma. From these data, we find that wet deposition dominates total deposition with dry deposition constitutes 12% of the total. These data also provide bounds on atmospheric lifetime with respect to deposition. We investigate the role of coated rBC particles as they may impact the lifetime and deposition rate of black carbon. Furthermore, we compare rBC fluxes measured by SP2 to the total aerosol burden (in the 60-700 nm diameter size range) measured by an ultra-high sensitivity aerosol spectrometer. These comparisons provide insight into parameters influencing the deposition rate of black carbon.