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

Abstract

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.