Two case-studies of atmospheric pollutant dispersion modelling over Alpine complex mountainous terrain

Two pollution episodes over the Aosta Valley (north-western Alps) are reconstructed using three modelling chains. The first analyzed episode occurred in winter 2017 and was dominated by synoptic-scale flows; the second occurred during summer 2015 and was dominated by thermally-driven winds. The modelling setup is based on two meteorological models: the Weather Research and Forecasting model (WRF) running at 0.5 km resolution and the Consortium for Small-scale Modelling model (COSMO-I2) operating routinely at 2.8 km resolution. The applied chemical transport model is the Flexible Air Quality Regional Model (FARM). Three different WRF configurations with specific planetary boundary layer and surface layer schemes are tested, and two different WRF-FARM runs are performed for each WRF configuration, using eddy diffusivities and turbulent scaling parameters computed by the FARM pre-processor (SURFPRO) or by WRF. Meteorological data computed by COSMO-I2 and the different WRF configurations are compared, and a comparison is also performed between numerical results and observed data in 24 meteorological stations. Chemical simulated data resulting from the different modelling chains are compared with each other, and with observations at 5 air quality stations.