Reaction of the Acetyl Peroxy Radical and OH Radical as a Source of Acetic Acid in the Atmosphere

The potential role of the reaction between the acetyl peroxy radicals (CH3C(O)O2) and the hydroxyl radical in the atmosphere was investigated. Theoretical calculations show that this reaction would form acetic acid (AAc) and 1O2 almost exclusively. The reaction proceeds by formation of a trioxide compound as CH3C(O)OOOH, in which rapid intramolecular hydrogen atom transfer followed by decomposition to AAc and 1O2 was found, while decomposition of the trioxide to CH3CO2 + HO2 is negligible. With the relatively fast reaction between CH3C(O)O2 and OH with an estimated rate coefficient of 1.8 × 10–10 cm3 molecule–1 s–1, the reaction might be a significant secondary source of AAc in the troposphere. A global atmospheric simulation using GEOS-Chem found that the title reaction results in an average increase of the mixing ratios of AAc by ∼33% (about 6.4 pptv for increase) and a net formation of about 8.0 Tg/yr AAc. Reactions between other RC(O)O2 and OH may also contribute significantly to the formation of RC(O)OH. The atmospheric chemistry model may need to include the title reaction.