Re-assessing hydroxyl radical chemistry in the atmosphere: Instrument interferences may explain previous measurement discrepancies

The hydroxyl radical controls the removal of many trace gases in the atmosphere and initiates the production of secondary pollutants such as ground-level ozone and secondary organic aerosols. An accurate understanding of the chemistry of this radical is important to understand the self-cleansing capability of the atmosphere and to develop effective control strategies. A previous assessment found that in some regions, measurements of the hydroxyl radical were up to ten times greater than predicted, suggesting an unknown chemical mechanism was responsible. However, recent measurements have revealed interferences associated with some instruments. Here we show that accounting for interferences results in measured hydroxyl radical concentrations that agree with model predictions over a wide range of conditions. This suggests that while there may be gaps in our knowledge of this chemistry in some environments, our understanding of hydroxyl radical chemistry and the self-cleansing capability of the atmosphere is better than previously believed. Measurement interferences may explain some discrepancies between hydroxyl radical measurement and modelling results, as opposed to an unknown chemical mechanism, according to analysis of hydroxyl measurement campaigns and model comparisons.