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 Data Photochemical Data
Content Table No. Fig. No.
Recommended Rate Coefficients 1
Reaction 1 CH3O2 + HO2 2 1
Reaction 2 CH3O2 + CH3O2 Kinetics 3 2,3
Reaction 2 CH3O2 + CH3O2 Product Branching Ratios 4 4
Reaction 3 CH3O2 + NO 5 5
Reaction 6 C2H5O2 + HO2 6 6
Reaction 7 C2H5O2 + NO 7
Reaction 9 CH3C(O)O2 + HO2 8 7
Reaction 10 CH3C(O)O2 + CH3O2 9 8
Reaction 11 CH3C(O)O2 + CH3C(O)O2 10
Reactions 12/13 CH3C(O)O2 + NO/NO2 11 9
Content Table No. Fig. No.
Recommended Absorption Cross Sections 12 10
Published Cross Sections for HO2 13 11
Published Cross Sections for CH3O2 14 12,13
Published Cross Sections for C2H5O2 15 14
Published Cross Sections for CH3C(O)O2 16 15