Observational Constraints on Wet and Dry Deposition of Black Carbon to Land Surfaces

Abstract

Removal of aerosols from the atmosphere occurs via wet and dry deposition. Black carbon (BC) is one form of aerosol that impacts atmospheric temperature, cloud formation and properties, the albedo of snow and ice surfaces, and the timing of snowmelt. Parameterization of BC dry deposition is particularly limited due to the lack of available instrumentation for measurement of the process, and thus the lack of observational datasets with which to evaluate existing models. The measurement of wet and dry deposition of BC may also provide insight on aerosol deposition in general, measurements of which can be challenging to interpret.
We propose to demonstrate the application of a Single Particle Soot Photometer (SP2) instrument to eddy covariance flux measurement of size-resolved rBC (core size and mixing size) through two 4-week sets of field measurements at the DOE ARM Southern Great Plains site. We will simultaneously measure eddy covariance flux measurements of size-resolved aerosol number fluxes with an ultra high sensitivity aerosol spectrometer (UHSAS) and collect precipitation samples for off-line measurement of rBC using a wet deposition collector. These data will allow us to investigate (1) To what extent dry versus wet deposition controls the removal of BC from the atmosphere, and thus atmospheric BC concentrations? (2) Is BC dry deposition controlled by the same processes as non-refractory aerosol dry deposition? This will allow us to determine whether BC deposition can be parameterized by the same models as other aerosol particles.
In particular, we will compare rBC dry deposition data from the SP2 eddy covariance measurements to the size-resolved resistance-in-series parameterizations for aerosol dry deposition that are typically used in chemical transport models. This comparison will allow us to evaluate the existing parameterizations for aerosol deposition, which are essential for understanding the contributions of uncertainty from BC and aerosol deposition to climate and air quality models.