Seasonal dependency of the atmospheric oxidizing capacity of the marine boundary layer of Bermuda

In this study, we investigate the atmospheric oxidation capacity in the marine boundary layer during two measurement campaigns in spring and summer 2019 at the Tudor Hill Marine Atmospheric Observatory, Bermuda. Measured species included non-methane hydrocarbons (NMHCs), HONO, HNO3, particulate matter, particulate nitrates, NO, NO2, O-3, in addition to the meteorological parameters. Measured concentrations of all species were generally higher in spring than in summer. During the spring and summer, OH initiation sources made 61% and 42% of the total OH production rate (P-OH) during the daytime, respectively. The higher levels of NMHCs and OH production from ozone photolysis lead to a higher oxidation rate of NMHCs in the spring compared to summer. However, the low NO in the spring and summer leads to inefficient recycling of RO2 and HO2 to OH, with HO2 reaction with NO accounting for only 22% and 42% of P-OH during spring and summer. Sensitivity analysis suggests that OH reactivity in the MBL can be potentially enhanced by an oceanic source rather than a secondary oxidation product. Including halogen monoxides, BrO and IO were found to decrease HO2 by similar to 14 and 18% during spring and summer, respectively, with marginal impact on OH due to the higher loss by aerosol uptake. The results demonstrate the complex multiphase HOx-Halogen chemistry and call for a more comprehensive multiphase investigation.