CALCULATION OF OZONE AND OTHER POLLUTANTS FOR THE SUMMER 1996: The Influence of Lateral Boundary Concentrations on Ozone Levels.

Results for the summer months April - September 1996 from the MA­ CHO model (Multi-layer Atmospheric CHemistry model, Oslo), a re­ gional scale photo-chemistry model, are presented and compared to measurements. Initial and lateral boundary concentrations are provided by a global CTM (Chemical Tracer Model). As a base run monthly averaged concentrations for June 1996 are used as initial and lateral boundary concentrations. The sensitivity of the interior model domain to the lateral bound­ aries is analyzed by comparing the base run with a model run with lateral boundary concentrations updated at six hour intervals. In the boundary layer over Europe differences between the two runs are small both for accumulated exceedances and for concentrations on individ­ ual days, indicating that ozone levels here are determined predomi­ nantly by local European scale sources. In the free troposphere however, the effects from the lateral boundary concentrations are shown to be significant.