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