Impact of the total aerosols solar extinction on photochemical pollution during the heat wave of summer 2003 over Western Europe

By controlling the abundance of photochemical pollutants, photolytic reactions plays a critical role in atmospheric chemistry. However, aerosols may alter photolysis rates by interacting with short-wave solar radiation, which in turn can modify associated concentrations of some gaseous compounds (ozone, nitrogen dioxide) and secondary aerosols species. In this study, we have developed an on-line coupling between the regional chemistry-transport model CHIMERE (associated with an aerosol optical module) and the radiative transfer code TUV to evaluate the impact of the aerosols solar extinction on photochemical pollution during the heat wave of summer 2003. Aerosols optical properties (aerosol optical thickness, single scattering albedo and asymmetry parameter), required in radiative transfer calculations, are modelled for three types of aerosol mixing: external, internally homogeneous and core-shell. Results of simulations, conducted over south-eastern France between 7 and 15 August 2003, show that the reduction of the NO2 and O3 photolysis rates, due to the aerosols solar extinction, decreases the mean daytime surface concentrations of ozone (0.5-4 %) and secondary aerosols (7-10 % for sulphates and 4-6 % for secondary organics), especially under the internal mixing assumption