An episode of photooxidant plume pollution over the Paris region

An ozone pollution episode typically at the mesoscale is studied for the period 17–20 July 1996 in the northern half of France. This episode has been documented through extra stations supplementing the regular French network in the southwest of the Paris region at large: the ozone threshold value of 90 ppb has been observed to be exceeded only at downwind rural stations at distances ranging between 25 and 110 km from downtown Paris. This episode has been simulated with the mesoscale model Meso-NH-C in which the meteorological model Meso-NH is coupled on-line with a chemistry module. Various assumptions are presented which must be made in order to run Meso-NH-C: e.g. reduction of the chemical scheme to reduce the computational costs or definition of procedures to fill in the lack of emission inventory data. Meso-NH appears to realistically simulate the position, extent, average and peak ozone values within the pollution plume. Sensitivity analyses emphasize, in particular, the need for accurate simulation of the wind field to capture correct characteristics of this plume.