Wet Scavenging in Cumulus-Parameterized WRF-Chem Simulations of a Supercell Storm during the DC3 Field Campaign

Deep convection can transport surface moisture and pollution from the planetary boundary layer (PBL) to the upper troposphere (UT) within a few minutes. The convective transport of surface ozone and precursors of ozone and aerosols from the boundary layer affects the ozone and aerosol concentrations in the UT, which will influence the Earth's radiation budget and climate. Some of the precursors are soluble and reactive in the aqueous phase. A number of physical processes within the convective core and anvil affect the net transport of soluble species by deep convective clouds, including dissolution in cloud water, removal by precipitation and evaporation and release of dissolved gases. When droplets freeze part of the dissolved gases may be released and part retained in ice. Collectively, these processes are referred to as wet scavenging. This study uses WRF-Chem to simulate the wet scavenging process of soluble ozone and aerosol precursors (such as HNO₃, CH₂O, CH₃OOH, H₂O₂, and SO₂) in a supercell system observed on May 29, 2012, during the 2012 Deep Convective Clouds and Chemistry (DC3) field campaign at cloud parameterized resolution. The WRF-Chem simulations underestimate the mixing ratios of soluble ozone precursors in the UT. In order to improve the model simulation of cloud parameterized wet scavenging, we added appropriate ice retention factors to the cloud parametrized wet scavenging module, and adjusted the conversion rate of cloud water to rain water in the cloud parametrization as well as in the subgrid wet scavenging calculation. The introduction of these model modifications greatly improved the model simulation of less soluble species (e.g. decreased the CH₂O simulation error by 12%, decreased the CH₃OOH simulation error by 63%, and decreased the H₂O₂ simulation error by 16%). In addition, we conducted a > 24-hour long simulation to examine downwind ozone production and its sensitivity to the ice retention factors.