Effect of vehicle fleet composition and mobility on outdoor population exposure: A street resolution analysis in Paris

High concentrations of health-related pollutants are observed in streets, inducing high outdoor population exposure. The impact of reducing traffic emissions on urban air quality is often quantified using regional-scale chemical-transport models (CTMs), which are representative of background concentrations but fail to represent the high street concentrations. Local-scale models may be more suitable to represent them, but their use for outdoor exposure assessments is still limited, because they often neglect secondary species, use simplified methods to estimate background concentrations, and omit/underestimate non-exhaust emissions. Here the impact of realistic and ambitious tendencies of vehicle fleet renewal and mobility on outdoor population exposure is investigated using multi-scale simulations. They are capable of representing secondary species in urban background and streets (including the formation of secondary organic and inorganic aerosols), and use non-exhaust emissions determined with a recently revisited approach. The 10-year vehicle fleet renewal induces large decreases in population exposure to NO2, black carbon, PM10, PM2.5, and organics. These decreases are stronger than estimated using CTMs. Favouring recent diesel, petrol, or electric vehicles, as proposed here, induces similar decreases of outdoor population exposure to PM2.5. Promoting electric vehicles induces the highest decrease of exposure to NO2. Home-office practice enhances the decrease of pollutant concentrations, but it is less effective than vehicle fleet renewal. However, much more ambitious reductions of pollutant emissions are still needed to respect air-quality guidelines.