Modeling of gas and aerosol with WRF/Chem over Europe: Evaluation and sensitivity study

The “online” meteorological and chemical transport Weather Research and Forecasting/Chemistry (WRF/Chem) model has been implemented over a European domain, run without aerosol‐cloud feedbacks for the year 2007, and validated against ground‐based observations. To this end, we integrated the European Monitoring and Evaluation Programme (EMEP) anthropogenic emission inventory into the model pre‐processor. The simulated average temperature shows a very small negative bias, the relative humidity and the wind speed are overpredicted by 1.5% (8%) and 1.0 m/s (76%), respectively. Hourly ozone (O 3 ) exhibits a correlation with observations of 0.62 and daily maxima are underestimated by about 4%. A general ozone underestimation (overestimation) is found in spring (fall), probably related to misrepresentation of intercontinental transport with time‐invariant boundary conditions. Daily nitrogen dioxide (NO 2 ) is reproduced within ±15% with a correlation of 0.57. Daily PM 2.5 aerosol mass shows mean bias of about −4.0 μ g/m 3 (−7.3%), mainly attributable to the carbonaceous fraction. The model underpredicts particulate sulphate by a factor of 2, and overpredicts ammonium and nitrate by about factor of 2. Possible reasons for this bias are investigated with sensitivity tests and revealed that the aqueous phase oxidation of sulphur dioxide (SO 2 ) by hydrogen peroxide (H 2 O 2 ) and O 3 , missing in the configuration of WRF/Chem without aerosol‐cloud feedbacks, explains the discrepancy.