P 2.20 Modelling Urban Area in Alpine Complex Terrain in Winter Time

Urban areas which are situated at the intersection of Alpine valleys are submitted to complex atmospheric flow patterns with significant impact on air quality. Local dynamics develop systems of slope and valley winds which interact ones with the others. Pollutants evolve according to chemical reactions homogeneously as gases and heterogeneously with particulate matters .There is a growing concern about PM10 and PM2.5 which are considered as harmful for health. They mostly come from combustion processes, directly or through chemical transformation : street and road traffic, industry and also domestic heating which is a significant contributor in winter at mid latitude. Atmosphere dynamics combine with chemistry in determining the evolution of these pollutants since they are transported from emission through winds which are highly changing along the day and with the location inside the area or interest. Dilution of chemical species is due to turbulence of the atmospheric flow. Consequently, it varies with time and in space.