Reaction between CH₃O₂ and BrO Radicals: A New Source of Upper Troposphere Lower Stratosphere Hydroxyl Radicals

Over the last two decades it has emerged that measured hydroxyl radical levels in the upper troposphere are often underestimated by models, leading to the assertion that there are missing sources. Here we report laboratory studies of the kinetics and products of the reaction between CH₃O₂ and BrO radicals that shows that this could be an important new source of hydroxyl radicals:BrO + CH₃O₂ → products (1). The temperature dependent value in Arrhenius form of <i>k</i>(<i>T</i>) is <i>k</i>₁ = (2.42_–0.72^+1.02) × 10^–14 exp­[(1617 ± 94)/<i>T</i>] cm³ molecule^–1 s^–1. In addition, CH₂OO and HOBr are believed to be the major products. Global model results suggest that the decomposition of H₂COO to form OH could lead to an enhancement in OH of up to 20% in mid-latitudes in the upper troposphere and in the lower stratosphere enhancements in OH of 2–9% are inferred from model integrations. In addition, reaction 1 aids conversion of BrO to HOBr and slows polar ozone loss in the lower stratosphere