Criegee Intermediate–Alcohol Reactions, A Potential Source of Functionalized Hydroperoxides in the Atmosphere

Ozonolysis, the mechanism by which alkenes are oxidized by ozone in the atmosphere, produces a diverse family of oxidants known as Criegee intermediates (CIs). Using a combination of newly acquired laboratory data and global atmospheric chemistry and transport modeling, we find that the reaction of CIs with alcohols, a reaction that was originally employed to trap these reactive species and provide evidence for the ozonolysis mechanism nearly 70 years ago, is occurring in Earth's atmosphere and may represent a sizable source of fiinctionalized hydroperoxides therein. Rate coefficients are reported for the reactions of CH2OO and (CH3)(2)COO with methanol and that of CH2OO with ethanol. Substitution about the Criegee intermediate is found to have a strong influence over the reaction rate, whereas substitution on the alcohol moiety does not. Although these reactions are not especially rapid, both the precursors to CIs and alcohols have large emissions from the terrestrial biosphere, leading to a high degree of co-location for this chemistry. We estimate that the products of these reactions, the alpha-alkoxyalkyl hydroperoxides (AAAHs) have a production rate of similar to 30 Gg year(-1). To assess the atmospheric lifetime of AAAHs, we used the nuclear ensemble method to construct a UV absorption spectrum from the four lowest energy conformers identified for a representative AAAH, methoxymethyl hydroperoxide. The computed absorption cross-section indicates that these compounds will be lost by solar photolysis, although not so rapidly as to exclude competition from other sinks such as oxidation, thermal decay, and aerosol uptake.