Local and regional contributions to photochemical atmospheric pollution insouthern France

In France, an important air quality surveillance network is organized by re gion. Each region has a number of measurement sites available. In southern France for each region studied, measurement sites show highly correlated va riations of daily ozone maxima during the summer periods (from April to Sep tember). Thus, we can calculate a mean regional distribution representative of each region considered. We can notice a high level of correlation betwe en mean regional distributions for different regions. The Marseilles and Ma rtigues areas are neighboring regions that show high correlation between ea ch 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 breez e effect coupled with daily erosion of the stable layer brings ozone and su lfur dioxide polluted air masses over the ground. Lastly, at a synoptic sca le, a Scandinavian anticyclone, spreading out over Western Europe and drift ing over the European continent, seems to be necessary and sufficient to th e formation of ozone episodes in the Marseilles and Martigues regions. (C) 2000 Elsevier Science Ltd. All rights reserved.