Evaluation of Meso-NH and WRF/CHEM simulated gas and aerosol chemistry over Europe based on hourly observations

International audienceGas and aerosol chemistry of 10 km -resolution mesoscale models Meso-NH and WRF/CHEM were evaluated on three cases over Europe. These one-day duration cases were selected from Freney et al. (2011) and occurred on contrasted meteorological conditions and at different seasons: a cyclonic circulation with a well-marked frontal zone on winter, an anti-cyclonic situation with local storm precipitations on summer and a cold front in the northwest of Europe associated to a convergence of air masses over eastern Europe and conflicting air masses over Spain and France on autumn. To assess the performance of the two models, surface hourly databases from observation stations over Europe were used, together with airborne measurements. For both models, the meteorological fields were in good agreement with the measurements for the three days. Winds presented the largest normalized mean bias integrated over all European stations for both models. Daily gas chemistry was reproduced with normalized mean biases between -14 and 11 %, a level of accuracy that is acceptable for policy support. The two models performances were degraded during night-time quite likely due to the constant primary species emissions. The PM2.5 bulk mass concentration was overestimated by Meso-NH over Europe and slightly underestimated by WRF/CHEM. The absence of wet deposition in the models partly explains the local discrepancies with the observations. More locally, the systematic low mixing ratio of volatile organic compounds in the gas phase simulated by WRF/CHEM at three stations was correlated with the underestimation of OM (Organic Matter) mass in the aerosol phase. Moreover, this mass of OM was mainly composed of anthropogenic POA (Primary Organic Aerosols) in WRF/CHEM, suggesting a missing source for SOA (Secondary Organic Aerosols) mass in WRF/CHEM aerosol parameterization. The contribution of OM was well simulated by Meso-NH, with a higher contribution for the summer case. For Meso-NH, SOA made the major contribution to the OM mass. The simulation of the mass of SO42- in particles by both models was often overestimated and correlated with an underestimation of the SO2 mixing ratio. The simulated masses of NO3- and NH4+ in particles were always higher for Meso-NH than for WRF/CHEM, which was linked to a difference in NOX mixing ratio between the models. Finally, computations of model performance criterion and model performance goals show that both models can be considered acceptable for standard modelling applications. In particular, Meso-NH model, using a gaseous chemical mechanism designed to compute the organic precursors of aerosols, shows comparable simulated amounts of SOA to observations at local sites