How different would tropospheric oxidation be over an ice‐free Arctic?

Climate projections suggest that a complete Arctic sea‐ice retreat is likely in the future during summer. Less ice will cause less light reflection and slower tropospheric photolysis. We use a tropospheric chemistry model to examine how oxidation may differ over an ice‐free Arctic. We find that late‐summer OH concentrations can decrease by 30–60% at polar latitudes, while effects on local ozone and global oxidant abundances are small. Ozone changes become larger in the more extreme case where sea‐ice is also removed in spring and early summer. In this case, we find large spring ozone increases (up to 50–60%) over the Arctic, and even over inhabited high latitude regions (up to 20%), due mainly to a reduction in the impact of bromine chemistry, caused by the sea‐ice retreat. Annual mean ozone also increases in the run with the summer/spring sea‐ice removal, but not in the simulation including only late‐summer sea‐ice removal.