A WRF-Chem Model Study of Aerosol Vertical Transport and Wet Scavenging in Deep Convection during the SEAC4 RS Field Campaign

Wet scavenging is the most dominant sink of aerosol particles, influencing the aerosol lifetime in the atmosphere. Wet scavenging in models is highly uncertain, especially for parameterized convective clouds hindering the accurate prediction of aerosol spatiotemporal distribution. In this study, we use the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) to examine the aerosol wet scavenging efficiency for the convective storms observed on 2 September 2013 near Jackson, MS during the NASA Studies of Emissions and Atmospheric Composition, Clouds, and Climate Coupling by Regional Surveys (SEAC⁴RS) field campaign observations. WRF-Chem is configured with three domains ranging from the regional scale (Dx = 12 km) over the conterminous US (CONUS) to the convective-permitting scale (Dx = 1.3 km) over the Mississippi region. Evaluating with NCEP Stage IV precipitation data and NEXRAD radar reflectivity, WRF-Chem produced precipitation and storms similar in character to those that were observed. Furthermore, the vertical profiles in the clear air region near the storms of the aerosol mass concentrations were compared well with the University of Colorado Aerosol Mass Spectrometer aboard the NASA DC-8 aircraft. Scavenging efficiencies (SE) for the aerosol mass concentrations are determined by analysis of the storm inflow and outflow regions from aircraft measurements and model simulations. The model simulated SE ranges from 50-60% for SO₄ and NH₄. Compared to observation-based analysis, the model underestimates the SE by 30-40%. Comparisons between the outer domain over CONUS and the convective-permitting domain over Mississippi provide information on the capabilities of the WRF-Chem with parameterized convection representing aerosol vertical transport and scavenging. The influence of major wet scavenging mechanisms (nucleation/impaction) is also investigated.