Inclusion of polar sea-ice emissions and sea-salt aerosol recycling of bromine into the global CAM-Chem chemistry-climate model

RAFAEL PEDRO FERNÁNDEZ; CARLOS ORDOÑEZ; DOUGLAS E. KINNISON; JEAN-FRANCOISE LAMARQUE; ALFONSO SAIZ-LOPEZ

Viena

Conferencia; European Geosciences Union General Assembly - (EGU 2013); 2013

European Geosciences Union

The global CAM-Chem chemistry climate model has been updated by including a coupled polar module with a full halogen chemistry mechanism and time-varying organic and inorganic halogen emissions into the polar marine boundary layer. The baseline halogen CAM-Chem setup has already been validated for the tropics and mid- latitudes and includes natural sources of very short-lived (VSL) halocarbons from the oceans; reactive chlorine, bromine and iodine species; related photochemical, gas-phase and heterogeneous reactions, as well as wet and dry deposition for relevant species. The coupled polar module considers i) time-dependent sea-ice emissions of Br2 and BrCl as result of recycling over the deposited snow over sea-ice, ii) sea-salt aerosol recycling of BrONO2 , BrNO2 and HOBr in the polar boundary layer and iii) improved sea-salt recycling efficiency over fresh sea-ice regions representing the contributions from blowing snow.The external brominated sources posses a 2-fold dependence on both solar zenith angle and local sea-ice cover. The time/sea-ice dependent local Br2 flux was scaled to reproduce observations of reactive bromine species over coastal Antarctica. This results in an Antarctic mean sea-ice flux of ∼200 Gg Br yr−1 with maximum emissions in late spring, as a compromise between sea-ice coverage and intensity of radiation. Recycling of bromine over sea-salt aerosol is the dominant factor controlling the tropospheric vertical column density (VCD) of BrO and other inorganic bromine species. A monthly-dependent depletion factor is introduced to account for the net fraction of Br in sea-salt that is released to the atmosphere.Model results have been validated locally against measurements of BrO performed at several Antarctic stations, showing a good agreement both in the boundary layer concentrations for the entire year and the springtime maxi-mum BrO observed in October. The seasonality and intensity of the BrO total and tropospheric columns are also in agreement with BrO VCDs results reported from satellite platforms, showing a polar BrO cloud distribution coincident with the Antarctic monthly sea-ice coverage. Further work will quantify the contribution of halogen chemistry to the oxidation capacity of the polar atmosphere.