• Arctic

[1] 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.