| 23 Jan 2026
Aerosol Scavenging in DC3 and SEAC4RS Deep Convective Storms
Abstract. 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 role 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. Production of organic acids in cloud water is shown to contribute to organic aerosol mass in the outflow regions for the mid-day storms sampled, which may explain why those storms have 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 as a way to evaluate convective storm processing of aerosols.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Chemistry and Physics.
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This manuscript derives composition-specific aerosol scavenging efficiencies (SE) through the analysis of ten storms 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. The manuscript addresses an important problem—quantifying composition-dependent aerosol scavenging in deep convection—and provides a valuable observational dataset. The results presented can be used directly for evaluating cloud-scale chemistry transport model representation of aerosol scavenging.
The article is written clearly and would be a good contribution to ACP. However, the authors need to address the following comments before I can recommend publication in ACP.
 Major comments:
The largest concern is the limited evaluation of uncertainty in entrainment rates and its propagation into scavenging efficiency (SE). Given that SE is directly dependent on the entrainment, a quantitative uncertainty analysis (e.g., sensitivity tests or error propagation) would substantially strengthen the robustness of the conclusions.
The discussion focuses primarily on chemical processes and entrainment of mid-free-tropospheric aerosol layers in interpreting SE variability. However, the dynamical controls on scavenging are less clearly developed. Although SE is shown as a function of the SWEAT index, the analysis does not fully explore how dynamical factors (e.g., convective intensity and updraft strength) may influence the observed chemical and scavenging signatures. The connection between storm dynamics and composition-dependent SE could be developed further, particularly in the Conclusions section.
Minor comments:
Tick directions are inconsistent across figures. For example, Fig. 4 and Fig. 6 have inward ticks, while other figures use outward ticks. Please standardize formatting.
Figure 2: It would be helpful to include the sample size (e.g., number of seconds of sampling) within each 1-km bin for the clear-air vertical profiles. Additionally, the method used to define the inflow aerosol concentration below cloud base should be clarified. Was the bin closest to cloud base used, or was an average taken across all sub-cloud layers?
Line 381: It would strengthen the discussion to provide references and typical magnitudes for below-cloud scavenging efficiency for comparison.
The Conclusions section would benefit from a brief, explicit statement of the main limitations of the study (e.g., entrainment uncertainty, tracer dependence, simplified chemical interpretation).