What are the Implications of Nonequilibrium in the O+OH and O+HO2 Reactions?

Abstract

Vibrationally excited O2, OH, and HO2 species have been suggested (J. Phys. Chem. A 2004, 108, 758) to provide clues for explaining the ldquoozone deficit problemrdquo and ldquoHOx dilemmardquo in the middle atmosphere under conditions of local thermodynamic disequilibrium (LTD), but the question arises of how much LTD will affect the title ozone sink reactions. Besides providing novel kinetic results, it is shown that LTD tends to disfavor ozone depletion relative to traditional atmospheric modeling under Boltzmann equilibration, which is partly due to competition between the various reactive channels. The calculations also suggest that the title LTD processes can be important sources of highly vibrationally excited O2 in the middle atmosphere. Moreover, LTD is shown to offer an explanation for the fact that some down revision of the O+HO2 rate constant, or the ratio of the O+HO2 to O+OH rate constants, is required to improve agreement between the predictions of traditional modeling and observation. This, in turn, provides significant evidence supporting LTD at such altitudes.