Application of a multiscale, coupled MM5/chemistry model to the complex terrain of the VOTALP valley campaign

A coupled complex meteorology/chemistry model has been used to simulate the how field and the concentration fields of atmospheric pollutants in Alpine valleys during the VOTALP (Vertical Ozone Transports in the ALPs) Valley C ampaign in August 1996 in southern Switzerland. This paper starts with a de scription of a coupled numerical model (MCCM, Multiscale Climate Chemistry Model), which is based on the Penn State/NCAR nonhydrostatic mesoscale mode l (MM5) and the RADM2 gas-phase chemical reaction scheme. The second part o f the paper presents a simulation for the Mesolcina Valley, the core region of the VOTALP Valley Campaign, and adjacent regions. The simulation was do ne using the nesting facility of the coupled meteorology/chemistry model. T he horizontal resolution for the innermost nest was 1 km. The simulations d epict the daily thermally induced valley and mountain wind system and the a dvection of pollutants with this wind system. It becomes obvious that in th e model simulation highly polluted air from the Po Basin is transported int o the Alpine valleys during the day. During the night cleaner air is brough t downward with the mountain winds. Cross sections from the high-resolution model results give a closer look at the inflow and outflow of pollutants i nto and from the Mesolcina Valley. (C) 2000 Elsevier Science Ltd. All right s reserved.