Mixing of boundary layer and upper tropospheric ozone during a deep convective event over Western Europe

Typically, during summer over Europe, pollution episodes in the boundary layer are interspersed with deep convective events which significantly redistribute all pollutants in the vertical. A 3D mesoscale model with an entraining/detraining plume model coupled on-line with gaseous chemistry (J. Geophys. Res., 2002, in press), is used to study the impact of deep convection upon the redistribution of ozone during a summer pollution episode over northern France combining both stratospheric ozone intrusion and enhanced upward transfers. The model reproduces well the ozone concentrations measured in the upper troposphere during two MOZAIC flights and, through sensitivity analyses, can clearly ascertain to convective transport a 110 ppb ozone peak at 6000 m. This study also emphasizes the impact of convective processes on the ozone spatial distribution near the surface. As a result, convective updrafts and downdrafts affect all chemical concentrations, particularly over a range of ±30 ppb in the ozone surface concentrations. At this stage, our conclusion is that deep convection not only modifies the ozone distribution in the mid and upper troposphere but also has a significant effect at the surface.