Oxidant Production over Antarctica Land and its Export – OPALE

The aim of OPALE is to establish the present-day oxidative capacity of the atmosphere over the Antarctic plateau, which appears to be unexpectedly strong due to the presence of the snow cover, to assess its influence on coastal Antarctica, and to forecast its future change in response to the recovery of the stratospheric ozone layer. Emission fluxes from snow of H2O2, HCHO, NO, NO2 and HONO which are suspected to contribute to the high levels of oxidants of the overlying atmosphere will be investigated at Concordia. The analysis of the O isotopes of NOx and O3 will give insights on the respective contribution of photolysis and re-emission leading to the loss of HNO3 from the snow reservoir. We will determine key physical parameters for re-emission of species from snow (temperature gradients in snow, specific surface area of snow, micrometeorology above the surface, penetration of solar radiation in snow). These parameters will be used as input for a coupled snow physics-chemistry model to parameterize the air-snow exchange of reactive species. We will deploy the new SAMU (ion chemistry mass spectrometer) instrument to measure OH radicals. Other key oxidants like O3 will be also measured. Obtained data will be used and evaluated with the photochemical box model CiTTyCAT that can be coupled to the trajectory/dispersion model FLEXPART, and which includes a comprehensive module of tropospheric chemistry. The parameterization of snow/air fluxes provided by the snow-pack model will be implemented in the photo-chemical model to simulate oxidants mass closure at Concordia. An external collaboration will be established with US colleagues conducting other experiments at South Pole in 2008/2009 (ISCAT IPY project). It is foreseen that Twin Otter will flight between South Pole and DC where profiles of key species (NO/NO2, O3, CO) will be established, greatly expending the spatial coverage of these species above the continent. The obtained parameterizations of the snow-air fluxes of relevant species will be implemented in the trajectory box model that will be integrated over multiple trajectories covering the Antarctic continent. The results will help to evaluate the representativeness of the local measurements within the Antarctic plateau. On this basis, model simulations will be iteratively compared with observations that are planned at the coastal Dumont d'Urville (DDU) site, a site which is exposed alternatively to inland Antarctic air mass flowed by the katabatic wind and pure marine advection in which the oxidative capacity is far more well understood. Finally modeling of the future change of the oxidative capacity of the atmosphere are aimed in view of the future recovery of stratospheric ozone layer over Antarctica.