Abstract
Escompte, a European programme which took place in the Marseille region in June–July 2001, has been designed as an exhaustive database to be used for the development and validation of air pollution models. The air quality Mesoscale NonHydrostatic Chemistry model (Meso-NH-C) is used to simulate 2 days of an Intensive Observation Period (IOP) documented during the Escompte campaign, June 23 and 24, 2001. We first study the synoptic and local meteorological situation on June 23 and 24, using surface and aircraft measurements. Then, we focus on the pollution episode of June 24. This study emphasizes the deep impact of synoptic and local dynamics on observed ozone concentrations. It is shown that ozone levels are due both to regional and local factors, with highlights of the importance of ozone layering. More generally this confirms, even in an otherwise predominant local sea-breeze regime, the need to consider larger scale regional pollutant transport.
Highlights
Escompte is a European programme designed to generate an exhaustive database for the development and validation of air pollution models (Cros et al, 2004)
Our aim here is to show how such circulations interact with local effects such as seabreeze regimes in the Escompte domain, resulting for example in the pollution episode observed on June 24 (IOP2b)
Our study takes place at the end of a mistral period in the Escompte domain and the onset of a sea-breeze regime on June 24. For such typical dynamical situations as the one from June 21 to 23, Millan et al (1996, 1997) explain how layering processes occur in the Western Mediterranean Basin (WMB)
Summary
Escompte is a European programme designed to generate an exhaustive database for the development and validation of air pollution models (Cros et al, 2004). There are strong industrial sources (the Berre pond accounts for 25% of the French Volatil Organic Compound (VOC) production), the large Marseille urban area (1 million inhabitants), a dense road and motorway network and strong biogenic emission sources This domain has been selected for its frequent and intensive summer photochemical pollution episodes. Our aim here is to show how such circulations interact with local effects such as seabreeze regimes in the Escompte domain, resulting for example in the pollution episode observed on June 24 (IOP2b) With this aim, we have used a 3D mesoscale model coupled on-line with a chemistry module (Section 2). The Meso-NH-C model is supplemented with a module of lagrangian diagnoses (Gheusi and Stein, 2002) These latter are not based on the computation of individual trajectories but rather on the on-line computation of three Eulerian passive tracers initialised with the Cartesian coordinates of each grid cell. The crucial problem of chemical initialisation in pollution simulations is solved by using the global chemistry transport model MOCAGE (Dufour et al, 2004) which gives boundary conditions to Meso-NH-C accounting for transboundary fluxes
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