Local and regional contributions to photochemical atmospheric pollution in southern France

In France, an important air quality surveillance network is organized by region. Each region has a number of measurement sites available. In southern France for each region studied, measurement sites show highly correlated variations of daily ozone maxima during the summer periods (from April to September). Thus, we can calculate a mean regional distribution representative of each region considered. We can notice a high level of correlation between mean regional distributions for different regions. The Marseilles and Martigues areas are neighboring regions that show high correlation between each other, but rather low with other regions. We observe in these two areas high levels of ozone and primary pollutants. This seems to be the result of phenomena from different scales. Indeed, at meso-scale, the land/sea breeze effect coupled with daily erosion of the stable layer brings ozone and sulfur dioxide polluted air masses over the ground. Lastly, at a synoptic scale, a Scandinavian anticyclone, spreading out over Western Europe and drifting over the European continent, seems to be necessary and sufficient to the formation of ozone episodes in the Marseilles and Martigues regions.