1Institute for Meteorology and Climate Research, Karlsruhe Institute of Technology, Karlsruhe, Germany
2School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA
3Institute of Chemical Engineering and High Temperature Chemical Processes, Foundation for Research and Technology Hellas (FORTH), Patras, Greece
4Laboratory for Air Pollution/Env. Technology, Empa Materials and Science, 8600 Duebendorf, Switzerland
Abstract. A Volatility Basis Set (VBS) approach for Secondary Organic Aerosol (SOA) formation is incorporated in the online coupled atmospheric model system COSMO-ART and applied over Europe during the EUCAARI May 2008 campaign. Organic Aerosol (OA) performance is improved when compared to the default SOA module of COSMO-ART (SORGAM) against high time resolution Aerosol Mass Spectrometer (AMS) ground measurements. This allows the investigation of SOA impact upon the radiative budget. The mean direct surface radiative cooling averaged over Europe is −1.2 W m−2 and contributes by about 20% to the total aerosol effect. Nevertheless, responses are not spatially correlated with the forcing, due to the nonlinear interactions among changes in particle chemical composition, water content, size distribution and cloud cover. These interactions initiated~by~the effect of SOA on radiation result even in a positive forcing over a limited surface and mostly where the net effect of interactions on the cloud cover is negative. Further model experiments showed that nitrogen oxides availability slightly affects SOA production, but the aging rate constant within the VBS approximation and the boundary concentrations assumed in the model should be carefully selected. SOA aging is found to reduce hourly nitrate levels up to 30%, while the condensation upon pre-existing, SOA-rich particles result in a monthly average increase of 5% in sulfate and ammonium formation in the accumulation mode.