Anthropogenic control over wintertime oxidation of atmospheric pollutants

Using airborne observations, we quantify the contribution of various oxidants on a regional basis during winter, enabling improved chemical descriptions of wintertime air pollution transformations.

We show that 25-60% of NOx is converted to N2O5 via multiphase reactions between gas-phase nitrogen oxide reservoirs and aerosol particles, with similar to 93% reacting in the marine boundary layer to form >2.5 ppbv ClNO2. This results in >70% of the oxidizing capacity of polluted air during winter being controlled by multiphase reactions and emissions of volatile organic compounds, such as HCHO, rather than reaction with OH.