Search for: All records

Deep convection can transport surface moisture and pollution from the planetary boundary layer to the upper troposphere (UT) within a few minutes. The convective transport of precursors of both ozone and aerosols from the planetary boundary layer affects the concentrations of these constituents in the UT and can influence the Earth's radiation budget and climate. Some precursors of both ozone and aerosols are soluble and reactive in the aqueous phase. This study uses the Weather Research and Forecasting model coupled with Chemistry (WRF‐Chem) to simulate the wet scavenging of precursors of both ozone and aerosols including CH₂O, CH₃OOH, H₂O₂, and SO₂in a supercell system observed on 29 May 2012, during the 2012 Deep Convective Clouds and Chemistry (DC3) field campaign at cloud‐parameterized resolution. The default WRF‐Chem simulations underestimate the mixing ratios of soluble ozone precursors in the UT because the dissolved soluble trace gases are not released when the droplets freeze. In order to improve the model simulation of cloud‐parameterized wet scavenging, we added ice retention factors for various species to the cloud‐parameterized wet scavenging module and adjusted the conversion rate of cloud water to rainwater at temperatures below freezing in the cloud parameterization as well as in the subgrid‐scale wet‐scavenging calculation. The introduction of these model modifications greatly improved the model simulation of less soluble species.

The convectively driven transport of soluble trace gases from the lower to the upper troposphere can occur on timescales of less than an hour, and recent studies suggest that microphysical scavenging is the dominant removal process of tropospheric ozone precursors. We examine the processes responsible for vertical transport, entrainment, and scavenging of soluble ozone precursors (formaldehyde and peroxides) for midlatitude convective storms sampled on 2 September 2013 during the Studies of Emissions, Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC⁴RS) study. Cloud‐resolving simulations using the Weather Research and Forecasting with Chemistry model combined with aircraft measurements were performed to understand the effect of entrainment, scavenging efficiency (SE), and ice physics processes on these trace gases. Analysis of the observations revealed that the SEs of formaldehyde (43–53%) and hydrogen peroxide (~80–90%) were consistent between SEAC⁴RS storms and the severe convection observed during the Deep Convective Clouds and Chemistry Experiment (DC3) campaign. However, methyl hydrogen peroxide SE was generally smaller in the SEAC⁴RS storms (4%–27%) compared to DC3 convection. Predicted ice retention factors exhibit different values for some species compared to DC3, and we attribute these differences to variations in net precipitation production. The analyses show that much larger production of precipitation between condensation and freezing levels for DC3 severe convection compared to smaller SEAC⁴RS storms is largely responsible for the lower amount of soluble gases transported to colder temperatures, reducing the amount of soluble gases which eventually interact with cloud ice particles.