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For example, ozone is a pollutant and greenhouse gas, and surface concentrations show both dramatic depletion near the sea-ice zone during polar spring and production above inner Antarctica during summer. To date our understanding of the chemical and natural air-snow processes remains incomplete, but is essential to guide legislation to control man-made emissions of ozone pre-cursor gases in the high latitudes.

This paper is a key contribution to the OPALE (Oxidant Production in Antarctic Lands and Export) project, a collaboration between BAS and four French partners, which seeks to understand air quality above snow in Antarctica. At Dome C, the drill site of the EPICA deep ice core, we carried out the first combined measurements of the nitrogen oxides NO and NO2, the main ozone precursors in the background atmosphere, alongside with other atmospheric key species. We sampled the air in the open pore space of the upper snowpack, as well of the lower atmosphere using a balloon, and measured atmospheric turbulence to quantify the upward mixing of trace gases emitted by the snowpack.

We find that, in contrast to South Pole, the air chemistry at Dome C in summer is strongly influenced by the diurnal cycle of solar irradiance and the sudden boundary layer collapse in the evening. Furthermore, the large concentrations of nitrogen oxide and flux observed are driven primarily by changes in snow chemistry, with smaller contributions from the variability in down-welling UV radiation. And finally, the observation of large NO2:NO ratios and low abundance of halogens points to yet unknown chemistry taking place in the air above the high and cold Antarctic Plateau.

These results will guide future studies, but also significantly improve model predictions of large-scale impacts of snowpacks on surface ozone concentrations as well as the interpretation of ice core records with regard to air quality in the past.