Publications

The reaction of hydroxyl and methylperoxy radicals is not a major source of atmospheric methanol

Caravan, Rebecca L.; Khan, M.A.; Zador, Judit Z.; Sheps, Leonid S.; Antonov, Ivan O.; Rotavera, Brandon; Ramasesha, Krupa R.; Au, Kendrew; Chen, Ming W.; Rösch, Daniel; Osborn, David L.; Fittschen, Christa; Schoemaecker, Coralie; Duncianu, Marius; Grira, Asma; Dusanter, Sebastien; Tomas, Alexandre; Percival, Carl J.; Shallcross, Dudley E.; Taatjes, Craig A.

Methanol is a benchmark for understanding tropospheric oxidation, but is underpredicted by up to 100% in atmospheric models. Recent work has suggested this discrepancy can be reconciled by the rapid reaction of hydroxyl and methylperoxy radicals with a methanol branching fraction of 30%. However, for fractions below 15%, methanol underprediction is exacerbated. Theoretical investigations of this reaction are challenging because of intersystem crossing between singlet and triplet surfaces – ∼45% of reaction products are obtained via intersystem crossing of a pre-product complex – which demands experimental determinations of product branching. Here we report direct measurements of methanol from this reaction. A branching fraction below 15% is established, consequently highlighting a large gap in the understanding of global methanol sources. These results support the recent high-level theoretical work and substantially reduce its uncertainties.