R. L. Caravan, M. A. H. Khan, J. Zádor, L. Sheps, I. O. Antonov, B. Rotavera, K. Ramasesha, K. Au, M.-W. Chen, D. Rösch, D. L. Osborn, C. Fittschen, C. Schoemaecker, M. Duncianu, A. Grira, Sebastien Dusanter, A. Tomas, C. J. Percival, D. E. Shallcross, C. A. Taatjes
Nature Communications, Vol. 9
Publication year: 2018

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.