1.3 Convective Transport of Peroxides by Thunderstorms Observed over the Central U.S. during DC3

Wednesday, 13 January 2016: 9:00 AM
Room 356 ( New Orleans Ernest N. Morial Convention Center)
Mary C. Barth, NCAR, Boulder, CO; and M. M. Bela, P. O. Wennberg, J. Crounse, J. St. Clair, and A. Fried

One of the objectives of the Deep Convective Clouds and Chemistry (DC3) field experiment was to make observations of soluble trace gases in the inflow and outflow regions of deep convection in order to determine the scavenging of these trace gases by thunderstorms. In this paper, we present an analysis of scavenging of hydrogen peroxide (H2O2) and methyl hydrogen peroxide (CH3OOH) from 6 thunderstorm cases that occurred in northeast Colorado and Oklahoma. Estimates of H2O2 scavenging efficiencies for the 6 cases analyzed ranged from 80-97% with uncertainties of 5-23%. These values are comparable to previous studies. On the other hand, CH3OOH scavenging efficiencies ranged from 12-84% with uncertainties of 13-64%. The wide range of CH3OOH scavenging efficiencies is surprising. It is expected, from previous studies, that CH3OOH scavenging efficiencies would be <10%. We discuss possible explanations for obtaining high CH3OOH scavenging efficiencies based on the 6 thunderstorm environments, morphology, and chemistry. The highest CH3OOH scavenging efficiencies occurred in two severe thunderstorms, but there is no obvious correlation between the CH3OOH scavenging efficiency and storm environment. While there was not a strong correlation between the CH3OOH scavenging efficiencies and ice water content, there was some correlation with the estimated entrainment rate of the 6 thunderstorm cases. The production of NO from lightning appears to influence CH3OOH scavenging by increasing the rate of the CH3OO + NO reaction which reduces the production of CH3OOH via CH3OO + HO2. It is hypothesized that the combination of large graupel regions, which is conducive for removal of cloud water (and its dissolved species) and for triggering lightning flashes, with the increase of NO from the lightning production are responsible for the high CH3OOH scavenging.
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