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Clouds and chemistry, deep convection, HOx precursors

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By using a three‐dimensional convective cloud model to simulate the 10 July 1996, Stratospheric‐Tropospheric Experiment: Radiation, Aerosols, and Ozone‐Deep Convection experiment storm, we investigate the fate of formaldehyde (CH2O), formic acid (HCOOH), hydrogen peroxide (H2O2), and methyl hydrogen peroxide (CH3OOH) in an isolated thunderstorm. CH2O, H2O2, and CH3OOH are important HOx radical and ozone (O3) precursors in the upper troposphere. Thus, determining their source strength to the upper troposphere is important for estimating O3 production. The model simulates O3‐NOx‐CH4 chemistry (no nonmethane hydrocarbon chemistry) which is affected by the cloud microphysics and production of NOx by lightning. The retention of the soluble species within ice, snow, and hail during drop freezing results in less transport of the species to the upper troposphere than when the species is degassed during drop‐freezing processes. Aqueous‐phase chemistry is found to be inadequate in producing sufficient quantities of HCOOH so that HCOOH could serve as a reliable indicator of cloud‐processed air. The production of nitrogen oxides by lightning has little to no effect on convective outflow mixing ratios of CH2O, H2O2, and CH3OOH within 100 km of the convective cores. Thus, it is unlikely that lightning affects concentrations of HOx precursors near active convection. Scavenging of CH2O and H2O2 significantly affects their concentrations in the convective outflow, although H2O2 mixing ratios were still similar to CH3OOH indicating that both peroxides can contribute equally to O3 production downwind of convection.

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Journal of Geophysical Research: Atmospheres, v. 112, issue D13, art. D13310

Copyright 2007 by the American Geophysical Union.