Observational Constraints on a Potential Source of Secondary Methanol

The reaction between methyl peroxy (CH₃OO) and hydroxyl (OH) radicals was recently demonstrated in laboratory experiments to proceed at a atmospherically relevant rate [0.8-2.8E-10 cm³ s⁻¹]. A minor branching from this reaction is calculated to yield methanol (CH₃OH). Global atmospheric models coupled with theoretical calculations suggest that this reaction may result in a secondary source of CH₃OH that rivals emissions from the terrestrial biosphere. In the remote atmosphere, methane (CH₄) oxidation by hydroxyl radicals (OH) produce methyl peroxy radicals (CH₃OO). In addition to its reaction with OH, CH3OO will undergo reaction with RO₂, a previously known source of methanol, or with either NO (to generate formaldehyde (CH₂O)) or HO₂ (to generate methyl hydrogen peroxide (CH₃OOH)), a relatively longer-lived radical reservoir. In-situ measurements of photolysis rates, CH₄, OH, HO₂, NO, CH₃OOH, CH₂O, CH₃OH, OH, and HO₂ from the ATom campaign offer observational constraints on the relative importance of these pathways with potential significance for persistent gaps in our understanding of global methanol and the oxidant budget in the remote atmosphere.