Estimating the effect of on-road vehicle emission controls on future air quality in Paris, France

For several years several vehicle emission control technologies have been developed and introduced to reduce the contribution of road traffic to air pollution. However, this contribution in the Île de France region, around Paris, France, has been estimated to still be significant. We present a modeling study of the effect of the future evolution of traffic emissions on air quality at the urban scale. The aim is to assess the respective contribution of the different processes involved in the nonlinear chemistry of photochemical air pollution (change in emissions and/or chemical behaviour) that explain the observed evolution of concentrations of traffic-related pollutants at monitoring urban background stations. The modeling results suggest that the reduction of NO_x emissions must be coupled with more stringent measures on NMVOC emissions than those currently planned in the transportation sector to avoid an increase of O₃ concentrations in some densely populated areas. The modeled NO₂ concentrations in Paris reach a maximum in 2010 due to an increase of the NO₂ emissions related to the evolution of the NO₂/NO_x ratio of the Diesel vehicle emissions. The reduction of PM emissions leads to a non-proportional decrease in PM concentrations, which results mostly from the decrease in Diesel particulate emissions.