Modelling particle number concentrations in a typical street canyon in Germany and analysis of future trends

An aerosol box model and a gas-phase chemistry box model were coupled to simulate particle number (PN) concentrations, both solid and volatile, in a typical street canyon with a high traffic volume in Germany. The simulation accounts for emission, nucleation and aerosol aging processes while dilution is parameterised by a simple two-stage process. Calculations were performed for the years 2010, 2015, 2020 and 2025, and for a vehicle fleet consisting of electric vehicles only (“electric mobility”). Projections including a high fraction of Euro-6 vehicles in the fleet suggest that PN emissions will reduce by 90% in 2025 compared to 2010. Ambient PN concentrations are, however, expected to reduce by merely 29% over the same period. Apart from contributions of urban background air, reductions in primary particles are partially offset by secondary particle formation by nucleating exhaust gases. In the “electric mobility” scenario omitting tailpipe emissions, PN concentrations are expected to reduce by 60% from 2010 to 2025. For an aerosol assumed to be mixed externally only, PN of elemental carbon (EC) was calculated to reduce by 76% from 2010 to 2025, in the “electric mobility” scenario by 87%. Overall, the contribution of solid PN emissions from gasoline vehicles to PN concentration in the street canyon is expected to be approximately 4% in 2025.