Convective Transport and Scavenging of Formaldehyde in Thunderstorms over the Central United States: Analysis of Measurements Acquired During the DC3 & SEAC4RS Studies (Invited Presentation)

Convective transport of the reactive and soluble trace gas formaldehyde (CH2O) is an important process by which precursors of ozone can be effectively transported from the boundary to the upper troposphere and lower stratosphere (UT/LS). At present, there are large uncertainties in determining the scavenging efficiencies (SEs) of soluble gases like CH2O during convective transport. The present talk will discuss 3 independent approaches in determining CH2O SEs during the 2012 Deep Convective Clouds and Chemistry (DC3) study. Analysis from this campaign relied heavily on non-reactive and non-soluble organic tracers: i/n-butane and i/n-pentane in determining lateral entrainment values during convection as well as their ratios to ensure that inflow and outflow airmasses did not have vastly different origins. This study also relied heavily on ground-based radars and the resultant images to further identify coherently related storm inflow and outflow time periods. Since in most cases there was a finite amount of time from the top of the convective core to the time of aircraft sampling in the anvil outflow, we developed a method to extrapolate back to the storm core to account for the resulting dilution/mixing and possibility of chemical transformations.

Formaldehyde SEs were also determined from direct core intercepts of weaker convective systems during the 2013 Studies of Emissions, Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) campaign. Such core intercepts simplified the determinations of CH2O SEs since it obviates the need for back extrapolations. However, since the core intercepts were only a few seconds in duration only fast tracers like CO and CO2 could be employed. Formaldehyde SE results from both campaigns will be presented and compared.