Influence of sea-ice-derived halogens on atmospheric HOx as observed in springtime coastal Antarctica

We present first observations of OH and (HO₂ + RO₂) carried out in Antarctica outside the summer season. Measurements were made over 23 days in spring at the coastal Antarctic station Halley. Increases in concentrations were evident during the measurement period due to rapidly increasing solar irradiance, and clear diurnal cycles were present throughout. There were also notable differences in air mass composition depending on wind direction. Air masses that had traversed the sea-ice-zone had both higher concentrations of OH and a larger OH:(HO₂ + RO₂) ratio. We use steady-state kinetic arguments and a 0-D box model to probe the chemical drivers. We find that differences in bromine chemistry, previously measured at Halley, are sufficient to account for the observed differences in OH concentration as well as the ratio. There is some evidence also that chlorine chemistry is influencing concentrations of RO₂.

Sea ice in the polar regions is undergoing considerable change. Our results suggest that changes in the characteristics and extent of the sea-ice-zone that lead to changes in abundance of atmospheric halogens, will also result in a change in OH. For example, a shift towards more new sea ice formation, with its higher salinity over multi-year ice, would be expected to increase the abundance of halogens; conversely, overall reduction in sea ice extent would ultimately reduce abundance of halogens. OH radicals play a key role in oxidation reactions that remove pollutants from the atmosphere. Especially given anticipated expansion of industrial activities in the Arctic, this is a further factor to take into account when considering the wider impacts of sea ice loss.