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

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.

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

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) 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.

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

Ozone and water vapor measurements by Raman lidar in the planetary boundary layer

The temporal and spatial retrieve of ozone (O3) concentration and water vapor (H2O) mixing ratio in the troposphere is of essential interest. Contrary to the stratospheric case, the tropospheric ozone can have a harmful impact, with its toxic effect, on humans and vegetation, accelerating the degradation of the minerals and participating in the green-house problem. Concerning the water vapor, knowledge of its highly variable concentration is essential to both the chemistry of the troposphere (O(1D) + H2O —> 2 OH) where it participates, among others, in the generation of the hydroxyl radical (OH) and to the meteorology. Water vapor is the dominant green-house gas, it plays an important role in the atmospheric chemistry. The conversion and transport of water in the atmosphere is the essential point in the earth's radiation budget. Due to the complexity and the non-linearity of the air pollution system including emissions, chemistry, thermal radiation, transport and deposition, pollution abatement strategies can only be designed rightly by the use of a three-dimensional mesoscale Eulerian photochemical transport model. To check such models, measurement campaigns are undertaken, in which many physical (wind, temperature, H2O, etc.) and chemical parameters (emissions and imissions) are measured at different parts of the atmosphere. LIDAR (LIght Detection And Ranging), which is a real-time method for measuring air pollutants in situ, is one of the best tools to make 3-D measurements of gases concentrations like O3, H2O and others. Contrary to the ground based measurements that are highly sensitive to the very local conditions, lidar sensitivity and resolution in space and time is optimal to obtain measurements and to compare or give some input data for the models. During the last thirty years, (elastic backscatter) Differential Absorption Lidar (DIAL) has been established as a convenient tool for the monitoring of the three dimensional real time concentrations of air pollutants [Measures, 1992], [Schoulepnikoff et al., 1998]. But the DIAL apparatus has shown limitations: — the operation in layers with high aerosol loading like in the Planetary Boundary Layer (PBL) where they are highly variable — the simultaneous detection of several atmospheric components or pollutants is impossible [Bösenberg, 1996] — the detection at short range is difficult due to the high dynamics. Furthermore, due to its spectrum and the strong influence from other elements, the water vapor can not be easily measured in the UV with classical DIAL systems. The goal of this work was to develop a method to simultaneously measure the ozone absolute concentration and the water vapor mixing ratio in the PBL. Experiments with Nd : YAG and KrF lasers were made and utilization of both analog and photon counting techniques, increasing the dynamic range, were investigated. To retrieve the ozone concentration profile, we take advantage of the simultaneous spontaneous Raman backscattering on the molecules of nitrogen (N2) and oxygen (O2) that have different ozone absorption cross-sections. Thus with a modified DIAL technique, the ozone concentration can be measured without most of the interference from poorly known backscatter by particles. Water vapor mixing ratio profile can also be obtained with a set of three Raman backscattered signals, simultaneously detected, from the molecules of H2O, N2 and O2. The main advantage of this Raman system is its essential independence to the wavelength dependent backscatter problems as induced by aerosols, and the fact that the N2 and O2 concentrations are well known as well as the Raman cross-sections of interest. Although the Raman cross-sections are two or three orders of magnitude lower than the elastic backscattering cross-sections, they are compensated by the proportionally much higher concentrations of O2, N2 and H2O compared to trace gases like O3. The development of the Raman — DIAL method for atmospheric measurements in the PBL presents several challenges. One is the development of highly-sensitive lidar systems, in particular the optical receiver, the spectrometer and the signal acquisition for the Raman part of the Raman-DIAL system. Also the data processing procedure for simultaneous evaluation of the ozone and the water vapor profiles. Both of these challenges present a number of issues, theoretical and practical, that are investigated in the frame of this work.

EPFL2001

Ozone and water vapor measurements by Raman lidar in the planetary boundary layer

EPFL2001

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

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

2002