References

ANGEO

Annales Geophysicae

ANGEO

Ann. Geophys.

1432-0576

Copernicus Publications

Göttingen, Germany

10.5194/angeo-24-2809-2006

Investigation of local meteorological events and their relationship with ozone and aerosols during an ESCOMPTE photochemical episode

Augustin

¹ Delbarre

¹ Lohou

² Campistron

² Puygrenier

² Cachier

³ Lombardo

Laboratoire de Physico-Chimie de l'Atmosphère, UMR CNRS 8101, Université du Littoral-Côte d'Opale, 189A, Avenue M. Schumann, 59140 Dunkerque, France

Laboratoire d'Aérologie, UMR 5560 CNRS/OMP/UPS, Centre de Recherches Atmosphériques, 65300 Campistrous, France

Laboratoire des Sciences du Climat et de l'Environnement, UMR CNRS-CEA 1572, avenue de la Terrasse, 91198 Gif sur Yvette, France

21 11 2006

24 11 2809 2822

2006

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The international ESCOMPTE campaign, which took place in summer 2001 in the most highly polluted French region, was devoted to validate air pollution prediction models. Surface and remote sensing instruments (Lidar, Radar and Sodar) were deployed over the Marseille area, along the Mediterranean coast, in order to investigate the fine structure of the sea-breeze circulation and its relationship with the pollutant concentrations. <br><br> The geographical situation of the Marseille region combines a complex coastline and relief which both lead to a peculiar behaviour of the sea-breeze circulation. Several local sea breezes, perpendicular to the nearest coastline, settled in during the morning. In the afternoons, when the thermal gradient between the continental and marine surface grows up, a southerly or a westerly sea breeze may dominate. Their respective importance is then a function of time, space and altitude. Furthermore, an oscillation of the westerly sea breeze with a period of about 3 h is also highlighted. <br><br> We show that these dynamical characteristics have profound influences on the atmospheric boundary-layer (ABL) development and on pollutant concentrations. In fact, the direction and intensity of the sea-breeze determine the route and the transit time of the stable marine air flow over the continental surface. Thus, the ABL depth may exhibit several collapses correlated with the westerly sea-breeze pulsation. The ozone and aerosol concentrations are also related to the dynamical features. In the suburbs and parts of the city under pulsed sea breezes, a higher ABL depth and higher ozone concentrations are observed. In the city centre, this relationship between pulsed sea-breeze intensity and ozone concentration is different, emphasising the importance of the transit time and also the build-up of pollutants in the marine air mass along the route. Finally, the variations of aerosol concentration are also described according to the breeze direction.

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