Étude d'un épisode photochimique à l'aide d'un modèle méso-échelle et de mesures intensives sur la région de Grenoble
The Grenoble metropolitan area located in the French Alps with more than 400 thousand inhabitants suffers from periods of high ozone (O3) concentrations in summertime. Grenoble is moreover located in the Y shaped convergence of three deep valleys with surrounding mountains up to 3 000 m above sea level (asl) leading to a very complex wind pattern. During summer 1999, a major field campaign GRENOble PHOTochemistry (GRENOPHOT) involving standard ground based stations, LIDAR, aircraft, DOAS, microwave windprofilers was carried out in order to obtain the measurements needed for model validation. The air quality model METeorological PHOtochemistry MODel (METPHOMOD) developed at the University of Bern and at the Swiss Federal Institute of Technology at Lausanne, was used to investigate the dynamic characteristics of air pollution in the Grenoble area during GRENOPHOT. The lumped chemical mechanism Regional Atmospheric Chemistry Mechanism (RACM) was used for the calculation. A one-way nesting technique was used in which the large grid is a squared 198 km one with a grid resolution of 6 × 6 km and the small one is a rectangular 78 x 68 km with a grid resolution of 2 × 2 km. There are 24 vertical levels up to 8 000 m asl. The meteorological and chemical simulations were validated with ground and vertical profiles measurements performed during the Intensive Observation Period (IOP) July, 25-27, when the O3 concentrations reached up to 95 ppb. Both the spatial as well as the temporal variabilities of the simulated O3 concentrations correspond reasonably well to the measured values. They catched the O3 plume south of Grenoble. The model results indicate a lower Planet Boundary Layer (PBL) height than the LIDAR observed. The PBL calculated by the model is about 2 100 m, whereas the LIDAR indicates about 2 400 m. The results show that the PBL in mountain terrain is higher than those found over flat terrain. A specific vertical stratification of the atmosphere at day and night time is observed during typical photochemical episodes. Highest O3 values appear in the south at 25 km downwind the city center, and the results show that about 32 ppb of fresh O3 are generated in the Grenoble plume.
Record created on 2011-02-16, modified on 2016-08-09