Effect of Marine and Land Convection on Wet Scavenging of Ozone Precursors Observed During a SEAC4RS Case Study

Convective clouds are important for both the vertical redistribution of tropospheric trace gases and the removal, via microphysical scavenging, of soluble trace gas precursors of ozone. We investigate wet scavenging of formaldehyde (CH2O), hydrogen peroxide (H2O2), and methyl hydrogen peroxide (CH3OOH) in quasi-marine and land convective storms over Texas, USA observed on 18 September 2013 during the 2013 SEAC(4)RS campaign. Cloud-resolving simulations using the Weather Research and Forecasting model with Chemistry (WRF-Chem) were performed to understand the effect of entrainment, scavenging efficiency (SE), and ice physics processes on these trace gases with varying solubility. While marine and land convection can have distinctly different microphysical properties, we did not find significant differences in the SEs of CH2O, H2O2, or CH3OOH. The SEs of 44%-53% for CH2O and 85%-90% for H2O2 are consistent with our previous studies from SEAC(4)RS and the 2012 DC3 field experiment storms. Using WRF-Chem simulations, the ice retention factor (r(f)) for CH2O was determined to be 0.5-0.9, which is higher than found in previous studies. We show that the CH2O r(f) is higher in airmass and multicell storms than in severe storms and hypothesize that ice shattering may affect CH2O r(f) values. The CH3OOH SEs (39%-73%) were higher than expected from Henry's Law equilibrium. While recent studies suggest that CH3OOH measurements have interference due to methane diol, we find that this interference cannot fully explain the higher-than-expected CH3OOH SEs determined here and during DC3, suggesting further research is needed to understand CH3OOH vertical redistribution.

Automated summary

Convective clouds play a significant role in redistributing trace gases in the atmosphere and removing soluble trace gas precursors. Our study focuses on the wet scavenging of formaldehyde (CH2O), hydrogen peroxide (H2O2), and methyl hydrogen peroxide (CH3OOH) during convective storms in Texas, USA. Using cloud-resolving simulations, we found that the scavenging efficiency of these gases was consistent across different types of convective storms. We also discovered higher ice retention factor for CH2O and unexpected results for CH3OOH, indicating the need for further research.