Aerosol scavenging in DC3 and SEAC⁴RS deep convective storms

Convective storms frequently occur over the central US during the late spring and summer impacting upper tropospheric composition, which in turn affects the radiative forcing of the climate system. Two important processes in deep convection are vertical transport and removal of trace gases and aerosols by microphysical scavenging. We calculate scavenging efficiencies of speciated aerosol mass concentrations based primarily on aircraft observations from the Deep Convective Clouds and Chemistry (DC3) and the Studies of Emissions, Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC⁴RS) field experiments combined with process-scale modeling. Sulfate and ammonium scavenging efficiencies are generally greater than 75 % for all storms analyzed. Particulate nitrate scavenging efficiencies are moderate (∼ 40 %). In some cases, the particulate nitrate concentrations are larger in the storm outflow region compared to the inflow region. Further analysis shows the roles of entrainment of mid-tropospheric particulate nitrate layers and lightning production of nitrogen oxides in affecting the particulate nitrate outflow concentrations. Organic aerosol scavenging efficiencies are greater than 75 % in severe storms, comparable to sulfate and ammonium, but ∼ 50 % for weak and moderate storms in the southern US where the chemical environment is different than the other storms sampled. Aqueous chemistry is shown to contribute to organic aerosol mass in the outflow regions for the mid-day storms sampled, potentially explaining their lower apparent scavenging efficiencies. These results, which highlight the complex interactions between dynamics, physics, and chemistry in thunderstorms, can be used by chemistry transport models to evaluate convective storm processing of aerosols.