Analysis of Convective Transport and Scavenging of Formaldehyde and Peroxides for Airmass Storms Observed during SEAC4RS Storms

Formaldehyde and peroxides are rapidly transported via deep convection from near the atmospheric boundary layer to the upper troposphere providing an influx of ozone precursors to the upper troposphere where ozone is radiatively active. Being soluble trace gases, formaldehyde and peroxides are removed to some degree by precipitation in deep convection. Previous studies from the Deep Convective Clouds and Chemistry (DC3) field experiment have determined the scavenging efficiency (SE) of formaldehyde to be 40-55%, hydrogen peroxide 75-95%, and methyl hydrogen peroxide 12-84% in severe convection, displaying a fairly wide range of estimates that may be affected by the storm microphysical processes. Scavenging efficiencies in weaker convection (e.g. airmass storms) have not been examined in as much detail. With updraft velocities <20 m/s and relatively little hail formation, airmass storms allow aircraft sampling through the storm core providing a means to obtain scavenging efficiencies without the uncertainties introduced by horizontal transport in the anvil region.

We analyze airborne and radar data from the NASA SEAC⁴RS field experiment to determine the scavenging efficiencies of formaldehyde and peroxides in airmass convective storms. Two approaches are used in this analysis. The first approach uses a simple entrainment model to find both the entrainment rate and scavenging efficiencies of soluble trace gases. The second approach compares the ratio of the soluble trace gas to CO in the outflow to that ratio in the inflow. Scavenging efficiencies for formaldehyde and peroxides are estimated for several small storms sampled on 2 September 2013 over central Mississippi and in both marine convection and convection in south-central Texas on 18 September 2013. Preliminary scavenging efficiency estimates for the 2 September case, based on data at ~8 km altitude, are 36-58%, 90%, 29%, and 96% for formaldehyde, hydrogen peroxide, methyl hydrogen peroxide, and hydroxy methyl hydrogen peroxide, respectively. These results are within the range determined from the DC3 analysis. WRF-Chem simulations of the 2 September case are used to determine the contributions of different cloud physics processes on predicted scavenging efficiencies.