3-DIMENSIONAL MODEL STUDIES OF EXCHANGE PROCESSES OF OZONE IN THE TROPOSPHERE OVER EUROPE

A three-dimensional Mesoscale Chemistry Transport (MCT) model driven by meteorological data from a Numerical Weather Prediction (NWP) model is used to calculate ozone and other chemical species over Europe over a 10-day period. The meteorological model uses cloud water as one of the prognostic variables and has an advanced treatment of stratiform and convective cloud and precipitation processes. In this way an improved resolution in time and space of cumulus cloud episodes is obtained with a better simulation of the convective transport as a consequence. It should also improve the computations of the photolysis rates which are highly dependent on cloud cover and cloud optical depth. The 10-day period (July 1-10, 1991) is characterized by warm weather and frequent occurrence of cumulus convection. The model results are compared to ground-based ozone measurements and ozone profiles. The results presented suggest that physical processes, especially convection, may dominate in the vertical distribution of ozone in the free troposphere, that sinking air which compensates for convective updrafts is important for the tropospheric ozone budget, and that transport of O-3 precursors from the boundary layer into the free troposphere by convection enhances the rate of O-3 production significantly. However, considerable uncertainty of the absolute magnitude of the convective mixing exists.