Oxidant production over Antarctica land and its export - OPALE

The atmosphere of the Earth is an oxidising medium. The atmosphere directly above the Antarctica plateau is thought to be a pristine clean environment, however the oxidising capacity of the Antarctic atmosphere has recently been found to be very high. Emission of nitrogen oxides (NO, NO2 and HONO) and oxidised compounds such as HCHO and H2O2 from the snowpack are thought to be responsible. The chemical emissions are mainly driven by photochemical reactions in the snow, i.e. the action of sunlight on snowpack drives photolysis of nitrate and hydrogen peroxide in the snow to produce fluxes of nitrogen oxides from the snowpack and hydroxyl radical reactions in the snowpack. Snow is an excellent medium for photochemical reactions owing to the enhancement in the light flux in the top 10cm of the snow relative to the atmosphere above. Previous studies of this snow-atmosphere chemistry have tended to concentrate on either atmospheric measurements and/or polar coastal sites. One aim of this investigation is to explore and explain the high atmospheric oxidising capacity over plateau continental Antarctica and link this chemistry with measurement and atmospheric chemistry/transport modelling studies with stations on costal Antarctica. Coastal Antarctic stations study a mixture of Antarctic and coastal air-masses. This study will be conducted at the important French/Italian ice-core drilling site at Dome C, located on the Antarctic plateau. Thus, the second aim of this work is to investigate the effect of air-snow chemistry on chemical records in ice cores used to infer previous climates. The proposed study is novel and excellent for three reasons: 1) The international team is investigating the snowpack chemistry AND the atmospheric chemistry. Many previous studies have tended to concentrate on the atmosphere, 2) The variation with depth of chemicals such as nitrate trapped in Antarctic ice cores potentially provides the strongest evidence available for past climate and climate change events, an understanding of which is required for the accurate predictions of future climate change. Deciphering the chemical signals present in the ice cores is a major challenge as various processes can lead to the loss of chemicals from the ice core after initial deposition. We propose to develop a method by which the nitrate profiles recorded in ice cores can be used to obtain oxidising capacity in past atmospheres. 3) The snow and ice at Dome C are not seasonal (no summer melting). This will be the first opportunity to measure photochemistry in snowpacks for non-seasonal snow and will be different to all previous work. The requested NERC support in this proposal is for the optical properties (albedo and light penetration depths of the Dome C snowpack to be measured, to monitor downwelling atmosphere radiation and the construction of a photochemical radiative transfer model to calculate photolysis rates of chemicals in the snowpack and fluxes of chemicals (NO, NO2, HONO etc) from the snowpack. This is a critical part of the international campaign which has British Antarctic survey (BAS) scientists measuring fluxes of these chemicals from the snowpack and three groups of French scientists measuring the snow microphysical structure, oxidants in the atmosphere and isotopic values of N and O in the snow and atmospheric modelling to explore the response of coastal stations to the interior oxidation chemistry as the air is transported away from the plateau to the coastal stations. The campaign is excellent value for money as the French Polar program IPEV is providing paid logistics. The proposal allows UK scientists access to the Antarctica Plateau, where the UK has no stations. This is a fantastic opportunity. The project partners are all world leading polar scientists. The campaign is an International Polar Year campaign under the International Global Atmospheric chemistry program (IGAC), AICI (air-ice chemical interactions) project.