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 flow field and the concentration fields of atmospheric pollutants in Alpine valleys during the VOTALP (Vertical Ozone Transports in the ALPs) Valley Campaign in August 1996 in southern Switzerland. This paper starts with a description of a coupled numerical model (MCCM, Multiscale Climate Chemistry Model), which is based on the Penn State/NCAR nonhydrostatic mesoscale model (MM5) and the RADM2 gas-phase chemical reaction scheme. The second part of the paper presents a simulation for the Mesolcina Valley, the core region of the VOTALP Valley Campaign, and adjacent regions. The simulation was done using the nesting facility of the coupled meteorology/chemistry model. The horizontal resolution for the innermost nest was 1 km. The simulations depict the daily thermally induced valley and mountain wind system and the advection of pollutants with this wind system. It becomes obvious that in the model simulation highly polluted air from the Po Basin is transported into the Alpine valleys during the day. During the night cleaner air is brought downward with the mountain winds. Cross sections from the high-resolution model results give a closer look at the inflow and outflow of pollutants into and from the Mesolcina Valley. (C) 2000 Elsevier Science Ltd.