This work focus on of the main physico-chemical processes driving the redistribution of photochemical pollutants and oxidizing capacity of the atmosphere, using the modelling way with the comprehensive RAMSChemistry meso-scale model. These studies were done in the framework of the ESCOMPTE models intercomparison modelling exercise. This experiment took place over the southern France, including the Marseilles urban area and close to the Fos-Berre industrial area. With the coupling of a chemical mechanism interpreter, a dry deposition module and an "online" photolysis rates calculation code, we were able to study the impact of these various processes on the distribution of pollutants and on the oxidizing capacity of the atmosphere. We shows that an "online" calculation for photolysis rates is necessary in order not to modify radicals redistribution, and that a simplified chemical mechanism is sufficient for processes studies, but not for air quality or oxidizing capacity prediction. Finally, the participation on the ESCOMPTE modelling exercise gave us the possibility to test in real conditions the RAMS-Chemistry model, and to compare it with reference models. It also permitted to focus on strong and weak points of this kind of exercises.
