Relative importance of organic coatings for the heterogeneous hydrolysis of N2O5 during summer in Europe

The heterogeneous reaction probability gamma N2O5 of N2O5 depends largely on the aerosol chemical composition. Several recent laboratory studies have shown that the presence of organic coatings on aqueous aerosols can suppress heterogeneous N2O5 hydrolysis. In this study we investigated the relative importance of organic coatings, formed via gas-to-particle conversion on aqueous aerosols, to N2O5 hydrolysis on local and regional scales during summer in Europe. We present results of one-dimensional process studies and of regional-scale model simulations for Europe with the comprehensive model system COSMO-ART. To treat N2O5 hydrolysis, we used recent results from laboratory studies that quantified gamma N2O5 on the basis of the organic coating thickness. The simulations showed that during any episode the conditions for formation of N2O5 and secondary organic compounds were very variable and depended strongly on the meteorological conditions. In regions of the model domain where both components were built-up, the formation of organic coatings could decrease particulate nitrate concentrations by up to 90%. Where these conditions were not met, the impact of the organic coating was negligible