The model reproduces the temporal variability of NO2, O3, PM10, PM2.5 better at rural than urban background stations. The fractional biases show that the model performs slightly better at RB sites than at UB sites for NO2, O3 and PM10. At UB sites, CHIMERE reproduces PM2.5 better than PM10. This is primarily the result of an underestimation of coarse particulate matter (PM) associated with uncertainties on SOA chemistry and their precursor emissions, dust and sea salt.