ECHANGES DANS LA COUCHE LIMITE ET LA BASSE TROPOSPHERE <br />ET CONSEQUENCES SUR LA POLLUTION<br />DANS LA REGION DE FOS-BERRE-MARSEILLE (EXPERIENCE ESCOMPTE).

The aim of this study is to analyse the vertical structure of the low troposphere during the ESCOMPTE campaign in relation with transport and diffusion of pollutants. This analysis shows the difficulty to define a boundary layer. It allows us to highlight a complexe superposition of several internal boundary layers, particularly near the coast. The study of the layer where pollution may be accumulated or diluted pointed out the fact that pollution is trapped near the surface, close to the coastline under sea-breeze conditions whereas it is advected over the mountains where the boundary layers are deeper. During sea-breeze conditions, the ozone concentration is paradoxically weak near the sources at the coastline (titration). Over the mountains, the strong developments of the boundary layers result in a mixing between the highly polluted low troposphere and the surface which enhances the ozone concentration.Cette étude porte sur les données de la campagne de mesure ESCOMPTE. Son but est d'analyser la structure verticale de la basse troposphère en liaison avec le transport et la diffusion des polluants. Cette analyse montre en particulier la difficulté à définir une couche limite comme on le fait classiquement. Elle permet de mettre en évidence la superposition complexe de couches limites internes, surtout près des côtes. L'étude de l'épaisseur de la couche dans laquelle la pollution est soit diluée, soit accumulée, montre que le mélange reste bloqué près de la surface, près des côtes par régime de brise de mer, alors qu'il est advecté et réparti sur une épaisseur plus conséquente sur les montagnes. Paradoxalement, la concentration en ozone sera, en régime de brise, plus faible en bordure de mer, près des sources (titration) alors que sur les montagnes, les forts développements de couche limite vont contribuer à intégrer de l'ozone de la basse troposphère, issu de couches limites lointaines, ce qui augmentera les concentrations locales

Echanges dans la couche limite et la base troposphère et conséquences sur la pollution dans la région de Fos-Berre-Marseille (Expérience ESCOMPTE)

TOULOUSE3-BU Sciences (315552104) / SudocTOULOUSE-Observ. Midi Pyréné (315552299) / SudocSudocFranceF

Study of the boundary layer: the 23th of june 2001 (IOP 2a) comparisons between data from model-aircraft-profilers network. The methodology

(janvier)

Comparison of pollution events during the ESCOMPTE 2001 campaign: sea-breeze and synoptic wind conditions

(août 2004)The ESCOMPTE experiment was dedicated to the study of pollution events. A brief description of this program is presented in the companion paper (Moppert et al.) which is devoted to the description of the thermodynamic environment including the vertical structure of the low troposphere, during an intensive observation period (IOP2). A few results are first recalled here. This latter paper focuses on the difference between the first two days (2001 June 22 and 23: IOP2a) when the Mistral mesoscale wind is blowing and the three following days (2001 June 24 to 26 : IOP2b) when sea-breeze conditions and a weak wind are encountered. The boundary layer (BL) development is typical of a sunny summer day on June 22 only, reaching heights (zi) of 1900m in the early afternoon. The advection of colder air from sea limits the BL development that hardly reaches 1000m during IOP2b. A mesoscale effect due to the high pressure situation induces downward mesoscale vertical velocities that stem the BL growth. On June 23, a negative mesoscale velocity, not explained yet, also prevents the BL from growing until 15 UTC. One location in the ESCOMPTE area does not follow these general features : it is the entrance of the Durance valley, to the North-East of the domain, where the valley wind added to the Ventury effect enhances high development of BL (up to 2500m). To study the possibilities of transfers of pollution between the BL and the staggered layers capping the BL, a preliminary analysis is made using June 24 ozone profiles, as tracers of the various air masses. Except for the case of the Durance valley, the transfers are, most of the time, limited to a few number of cases and to a small depth in the low troposphere, due to the weakness of the BL developments

Photochemical pollution episodes during ESCOMPTE 2001 under sea-breeze or synoptic wind conditions

(2-4 février 2005

Pollution transport and exchange during ESCOMPTE, 2nd IOP.

(2-4 février 2005

Stratification of the lower troposphere during the ESCOMPTE campaign

Implementation of adapted air quality policies and prediction of pollution events require the improvement of our understanding of combined chemical and dynamical processes which lead to high pollutants concentration in the atmospheric boundary layer. The ESCOMPTE program was devoted to establish a detailed 3-D database of primary pollutant emissions together with the dynamics and chemical composition of the atmosphere in order to validate and improve chemistry transport models. The ESCOMPTE experiment took place in the early summer of 2001, in the south-eastern part of France where the combination of high urbanization and industrialization with hot and sunny weather enhances photochemical pollution events. Due to the complex terrain of this region (both coastal and moderately mountainous area, channeling effects of the Rhône and Durance valleys,…), a preliminary effort is necessary to study the atmospheric dynamics in this heterogeneous region in relation with larger scales processes. The main objectives of this paper is to present the vertical structure of the ESCOMPTE area during different meteorological conditions of the second intensive observation period (IOP2) which lasted from June 22 to June 26

Atmospheric boundary layer depth and study of mesoscale impact during ESCOMPTE IOP 2.

(2-4 février 2005

Determination of turbulent parameters in the atmospheric boundary layer with an UHF wind profiler. Comparison with in situ measurements

(Août 2004)This study presents methods to determine turbulent parameters in the ABL with UHF wind profilers. These methods are compared with aircraft data measured during TRAC-98 campaign. The results of this comparison show that : (i) the turbulent kinetic energy dissipation rate measured by both instruments are well correlated with a slightly overestimation and underestimation of the UHF radar below and above 0.7Zi respectively ; (ii) the momentum fluxes measured by the UHF profiler is the same order of magnitude than the aircraft ones but is globally underestimated in the ABL, which can be the consequence of the larger turbulent scales not took into account by this instrument (keeping out the levels inferior to 0.3Zi where ground echoes perturb UHF profiler measurements) ; (iii) the sensible heat fluxes measured by both instruments are well correlated with a slightly overestimation of the UHF radar mainly caused by the overestimation of the dissipation rate and losses of mechanical production below and above 0.7Zi respectively

Trajectory derived from the 3D linear wind field retrieved by a wind-profiler mesoscale network

A key issue in the survey or analysis of pollution episodes lies in the documentation of the turbulent dispersion and transport of the pollutant in the atmospheric boundary layer (ABL). Usually these processes are investigated with numerical modeling. Actually with the rapid development of UHF wind profilers able to provide wind components, turbulent variables, mixing height with a fine time and vertical resolution in the ABL, we can expect in a very near future the set up of regional profiler networks devoted to real time pollution monitoring. Toward this expectation we present and discuss a methodology, based on measurements made by a wind-profiler mesoscale network, which retrieves the 3D wind field (linear part) used to derive any type of air parcel trajectories. The technique is applied to observations collected during the ESCOMPTE campaign, devoted to pollution studies, which took place in France in the early summer 2001 in the Marseille region, along the Mediterranean coast. In situ aircraft measurements and constant volume balloon trajectories are used to compare and verify the performance of this based-radar methodology during sea and land breeze events. These cases studies, characterized by rapid temporal evolution and important spatial variations of the atmospheric fields, are particularly instructive in the analysis of the potentiality of the techniqu