3D-air quality model evaluation using the Lidar technique

Abstract : This paper reports on a model investigation of a particular episode of tropospheric ozone formation in the city of Lyon, France. A large-scale measurement campaign involving ground-based analyzers, sampling, Sodars and Lidars has been used to validate the model results. Based on validated meteorological data and primary pollutant concentrations, the numerical model has been run to obtain 3D ozone concentration profiles during the whole campaign (22-25 June 1999). The results are compared to the ozone Lidar vertical profiles. Good agreement between Lidar data and model predictions is first obtained on 22 June (but not on the following days). On 23 and 24 June, ozone concentrations are significantly underestimated by the model. The ozone Lidar measurements allowed identifying large import processes from high altitudes that explain the difference. In a second model simulation, these imports are taken into account as new boundary conditions. This yielded good agreement between the experimental data and the predicted ozone concentrations over the whole period. The evidence of high altitude ozone intrusion is confirmed by back-trajectories calculations.