Design and validation of a multiphase 3D model to simulate tropospheric pollution

This work presents the Transport and Chemical Aerosol Model (TCAM) formulation and its validation in the frame of CityDelta-CAFE project. TCAM is a 3D eulerian multiphase model simulating tropospheric secondary pollution at mesoscale. It is included in the GAMES (Gas Aerosol Modelling Evaluation System) modelling system, designed to support the analysis of secondary pollution dynamics and to assess the impact of emission control strategies. The presented validation assessment has been performed in the frame of the CityDelta II project over the Milan domain and concerns both gas and aerosol 1999 simulations. Ozone, nitrogen oxides and aerosol computed and observed patterns have been compared and analysed by means of statistical indicators showing high model performances for both winter and summer pollution regimes.

Numerical study on the ozone formation inside street canyons using a chemistry box model

Tropospheric ozone is a secondary air pollutant produced in the presence of nitrogen oxides (NOx), volatile organic compounds (VOCs), and solar radiation. In an urban environment, ground-level vehicular exhaust is the major anthropogenic source of ozone precursors. In the cases of street canyons, pollutant dilution is weakened by the surrounding buildings that creates localized high concentration of NOx and VOCs, and thus leads to high potential of ozone formation. By considering the major physical and chemical processes, a chemistry box model is employed to investigate the characteristics of ozone formation due to vehicular exhaust inside street canyons under the worst case scenario, i.e. the calm wind condition. It is found that a high level of ozone concentration, of the order of 100 ppbv and higher, would occur inside the street canyons, in particular, when the emission rate (concentration) ratio of VOCs to NOx is greater than 10. This elevated ozone concentration appears at the transition from VOCs to NOx sensitivity and may extend to a few hundreds.