Comparison of pollution events during the ESCOMPTE 2001 campaign: sea-breeze and synoptic wind conditions (formerly paper 3.2)

The ESCOMPTE campaign took place in one of the most polluted area in France: strongly urbanized and industrial areas, important traffic, proximity to the Mediterranean sea, influence of sea- and land-breezes, rough topography. The work presented here is an experimental comparison between two situations of different synoptic conditions: the first one is a case of moderate to strong orographic wind likely to reduce pollution. The second is a case of sea-breeze reinforced by a light mesoscale component. The discussion is based on the measurements provided by aircraft, an ozone lidar and a network of UHF radars and sodars.

First the impact of dynamics will be described and used to explain the chemical processes. The steering mechanisms that will be pointed out will be confirmed and more thoroughly analysed with the help of a simulation from the non hydrostatic Mesonh-C mesoscale model and backwards trajectories obtained either with the model or with the profilers network. Constant volume balloons measurements will be also used to follow the air mass transport. The boundary layer structure and topography of the boundary layer top will be thoroughly investigated in order to be able to highlight the major role of transport and diffusion.