Étude d'un épisode photochimique à l'aide d'un modèle méso-échelle et de mesures intensives sur la région de Grenoble

The Grenoble metropolitan area located in the French Alps with more than 400 thousand inhabitants suffers from periods of high ozone (O3) concentrations in summertime. Grenoble is moreover located in the Y shaped convergence of three deep valleys with surrounding mountains up to 3 000 m above sea level (asl) leading to a very complex wind pattern. During summer 1999, a major field campaign GRENOble PHOTochemistry (GRENOPHOT) involving standard ground based stations, LIDAR, aircraft, DOAS, microwave windprofilers was carried out in order to obtain the measurements needed for model validation. The air quality model METeorological PHOtochemistry MODel (METPHOMOD) developed at the University of Bern and at the Swiss Federal Institute of Technology at Lausanne, was used to investigate the dynamic characteristics of air pollution in the Grenoble area during GRENOPHOT. The lumped chemical mechanism Regional Atmospheric Chemistry Mechanism (RACM) was used for the calculation. A one-way nesting technique was used in which the large grid is a squared 198 km one with a grid resolution of 6 × 6 km and the small one is a rectangular 78 x 68 km with a grid resolution of 2 × 2 km. There are 24 vertical levels up to 8 000 m asl. The meteorological and chemical simulations were validated with ground and vertical profiles measurements performed during the Intensive Observation Period (IOP) July, 25-27, when the O3 concentrations reached up to 95 ppb. Both the spatial as well as the temporal variabilities of the simulated O3 concentrations correspond reasonably well to the measured values. They catched the O3 plume south of Grenoble. The model results indicate a lower Planet Boundary Layer (PBL) height than the LIDAR observed. The PBL calculated by the model is about 2 100 m, whereas the LIDAR indicates about 2 400 m. The results show that the PBL in mountain terrain is higher than those found over flat terrain. A specific vertical stratification of the atmosphere at day and night time is observed during typical photochemical episodes. Highest O3 values appear in the south at 25 km downwind the city center, and the results show that about 32 ppb of fresh O3 are generated in the Grenoble plume.

Study of a photochemical episode over the Grenoble area using a mesoscale model and intensive measurements

Ioan Balin, Bertrand Calpini, Alain Clappier, Olivier Couach, Pablo Roberto Ristori, Valentin Simeonov, Hubert van den Bergh

The Grenoble metropolitan area located in the French Alps with more than 400 thousand inhabitants suffers from periods of high ozone (O3) concns. in summertime. Grenoble is moreover located in the Y shaped convergence of three deep valleys with surrounding mountains up to 3,000 m above sea level (asl) leading to a very complex wind pattern. During summer 1999, a major field campaign GRENOble PHOTochem. (GRENOPHOT) involving std. ground based stations, LIDAR, aircraft, DOAS, microwave windprofilers was carried out in order to obtain the measurements needed for model validation. The air quality model METeorol. PHOtochem. MODel (METPHOMOD) developed at the University of Bern and at the Swiss Federal Institute of Technol. at Lausanne, was used to investigate the dynamic characteristics of air pollution in the Grenoble area during GRENOPHOT. The lumped chem. mechanism Regional Atm. Chem. Mechanism (RACM) was used for the calcn. A one-way nesting technique was used in which the large grid is a squared 198 km one with a grid resoln. of 6 * 6 km and the small one is a rectangular 78 * 68 km with a grid resoln. of 2 * 2 km. There are 24 vertical levels up to 8,000 m asl. The meteorol. and chem. simulations were validated with ground and vertical profiles measurements performed during the Intensive Observation Period (IOP) July, 25-27, when the O3 concns. reached up to 95 ppb. Both the spatial as well as the temporal variabilities of the simulated O3 concns. correspond reasonably well to the measured values. They caught the O3 plume south of Grenoble. The model results indicate a lower Planet Boundary Layer (PBL) height than the LIDAR obsd. The PBL calcd. by the model is about 2,100 m, whereas the LIDAR indicates about 2,400 m. The results show that the PBL in mountain terrain is higher than those found over flat terrain. A specific vertical stratification of the atm. at day and night time is obsd. during typical photochem. episodes. Highest O3 values appear in the south at 25 km downwind the city center, and the results show that about 32 ppb of fresh O3 are generated in the Grenoble plume.

2002

An investigation of ozone and planetary boundary layer dynamics over the complex topography of Grenoble combining measurements and modeling

Ioan Balin, Bertrand Calpini, Olivier Couach, Pablo Roberto Ristori, Valentin Simeonov, Hubert van den Bergh

This paper concerns an evaluation of ozone (O-3) and planetary boundary layer (PBL) dynamics over the complex topography of the Grenoble region through a combination of measurements and mesoscale model (METPHOMOD) predictions for three days, during July 1999. The measurements of O-3 and PBL structure were obtained with a Differential Absorption Lidar ( DIAL) system, situated 20 km south of Grenoble at Vif (310m ASL). The combined lidar observations and model calculations are in good agreement with atmospheric measurements obtained with an instrumented aircraft (METAIR). Ozone fluxes were calculated using lidar measurements of ozone vertical profiles concentrations and the horizontal wind speeds measured with a Radar Doppler wind profiler (DEGREANE. The ozone flux patterns indicate that the diurnal cycle of ozone production is controlled by local thermal winds. The convective PBL maximum height was some 2700 m above the land surface while the nighttime residual ozone layer was generally found between 1200 and 2200 m. Finally we evaluate the magnitude of the ozone processes at different altitudes in order to estimate the photochemical ozone production due to the primary pollutants emissions of Grenoble city and the regional network of automobile traffic.

Copernicus Publications2003

Une première mesure lidar combinée d'ozone et de vent, à partir d'une instrumentation et d'une méthodologie coup par coup

During these last decades, air pollution has drawn the attention of scientists because of the deterioration of the human environment that it has caused. Unfortunately, the study of this dynamic phenomenon is very complex and requires the use of models that compute the evolution of the physico-chemical parameters of the atmosphere. Moreover, the predictions of the numerical simulations have to be validated by range- and time-resolved measurements, carried out continuously up to the top of the planetary boundary layer. Only the optical radar or lidar satisfies these specifications: for this reason the Laboratory for Air and Soil Pollution (LPAS) of the Swiss Federal Institute of Technology (EPFL) has developed such a system in order to provide the modellers with information complementary to that given by the ground measurements. This instrument, after mounting on a mobile platform, has determined the concentration of the key molecule ozone during several field campaigns, demonstrating its reliability and precision. Moreover, the EPFL system is a shot per shot lidar, able to record each detected signal and not only its average in a time interval. This feature is innovative to lidar determinations of tropospheric ozone and allows one to measure accurately the statistical error, to correct for the effect of systematic biases and to observe the dynamic behaviour of the atmosphere: the measurement of the statistical error has been used to build a model of the signal and of its noise, useful in the design of future lidar systems and for the comparison of the various data processing algorithms. the correction of the bias caused by the artificial deformation of the statistical distribution of the signal at long distance has led to a considerable increase of the range of the retrieved ozone profiles, the observation of the dynamic behaviour of the atmosphere has resulted in the first simultaneous measurement of a pollutant concentration and of the wind velocity with the same data set recorded by a lidar.

EPFL1996

Study of a photochemical episode over the Grenoble area using a mesoscale model and intensive measurements

Ioan Balin, Bertrand Calpini, Alain Clappier, Olivier Couach, Pablo Roberto Ristori, Valentin Simeonov, Hubert van den Bergh

2002

Une première mesure lidar combinée d'ozone et de vent, à partir d'une instrumentation et d'une méthodologie coup par coup

EPFL1996