Content - Small Organic Peroxy Radicals

Atmospheric Chemistry of Small Organic Peroxy Radicals

Global atmospheric models play a key role in international assessments of the human impact on global climate and air pollution. To increase the accuracy and facilitate comparison of results from such models it is essential they contain up-to-date chemical mechanisms. To this end we present an evaluation of the atmospheric chemistry of the four most abundant organic peroxy radicals: CH3O2, C2H5O2, CH3C(O)O2, and CH3C(O)CH2O2. The literature data for the atmospheric reactions of these radicals are evaluated. In addition, the ultraviolet absorption cross sections for the above radicals and for HO2 have been evaluated. The absorption spectra were fitted to an analytical formula, which enabled published spectra to be screened objectively. Published kinetic and product data were reinterpreted, or in some case reanalyzed, using the new cross sections, leading to a self-consistent set of kinetic, mechanistic and spectroscopic data. Product studies were also evaluated. A set of peroxy radical reaction rate coefficients and products are recommended for use in atmospheric modeling. A 3-D global chemical transport model (IMAGES) was run using both previously recommended rate coefficients and the current set to highlight the sensitivity of key atmospheric trace species to the peroxy radical chemistry used in the model.

The following tables and figures show the data used in the evaluation of peroxy radical reactions. For a more detailed discussion please refer to Tyndall et al. (2001). Address questions or comments to G. Tyndall. Photochemistry Figures and Tables compiled by Hannelore Keller-Rudek, MPI Mainz.

Kinetics DataPhotochemical Data
ContentTable No.Fig. No.
Recommended Rate Coefficients1
Reaction 1 CH3O2 + HO221
Reaction 2 CH3O2 + CH3O2 Kinetics32,3
Reaction 2 CH3O2 + CH3O2 Product Branching Ratios44
Reaction 3 CH3O2 + NO55
Reaction 6 C2H5O2 + HO266
Reaction 7 C2H5O2 + NO7
Reaction 9 CH3C(O)O2 + HO287
Reaction 10 CH3C(O)O2 + CH3O298
Reaction 11 CH3C(O)O2 + CH3C(O)O210
Reactions 12/13 CH3C(O)O2 + NO/NO2119
ContentTable No.Fig. No.
Recommended Absorption Cross Sections1210
Published Cross Sections for HO21311
Published Cross Sections for CH3O21412,13
Published Cross Sections for C2H5O21514
Published Cross Sections for CH3C(O)O21615