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

A three-dimensional Mesoscale Chemistry Transport (MCT) model driven b y 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 a nd convective cloud and precipitation processes. In this way an improv ed 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-d ay period (July 1-10, 1991) is characterized by warm weather and frequ ent occurrence of cumulus convection. The model results are compared t o ground-based ozone measurements and ozone profiles. The results pres ented suggest that physical processes, especially convection, may domi nate in the vertical distribution of ozone in the free troposphere, th at sinking air which compensates for convective updrafts is important for the tropospheric ozone budget, and that transport of O-3 precursor s from the boundary layer into the free troposphere by convection enha nces the rate of O-3 production significantly. However, considerable u ncertainty of the absolute magnitude of the convective mixing exists.