Simulation of ozone during the August 2003 heat wave and emission control scenarios

During August 2003, western European countries witnessed an unpreceeded 15-day long heat wave with record temperatures and unusually persistent high-ozone concentrations. In France, about 15 000 extra deaths occurred during this period. The study of photochemical smog during this episode is of primary interest since weather conditions were so extreme for western Europe that they provide a worst case scenario for air quality. This episode also provides an interesting benchmark for the evaluation air quality models. We present and evaluate the results of a regional simulation of the episode with the CHIMERE chemistry-transport model. In a reference run, the simulated ozone concentrations are compared to surface observations obtained from 237 monitoring stations in Europe. Statistical scores on diurnal cycle, daily maxima, spatial structure of ozone concentrations, and AOT60 show that the simulated values compare very well with the observed ones, although extreme ozone peaks are underestimated probably due to a lack of model resolution. We describe the simulated impacts on ozone of theoretical emission reduction scenarios. The current European legislation should lead in 2010 to a drastic reduction of health exposure (about half), as measured by the AOT60 indicator, and of the number of 180 μg m −3 exceedance hours (74% reduction). “Emergency” scenarios, with an assumed 20% emission reduction throughout Europe, would also be efficient (AOT60 indicator reduced by 28%). Over France, the efficiency of a national emergency scenario would be only about 2/3rd of that of a Europewide scenario. When the reduction starts after a few episode days, the time taken for the reduction to reach its full impact is about 3 days. Finally, it is shown that reduction of NO x emissions is twice as efficient as reduction in volatile organic compounds emissions.