A prototype of a micro-scale model for the distribution of NO2 in urban areas

We present a new 2.5D model for predicting the concentration of nitrogen dioxide (NO2) at street level in an urban area. This work develops the first prototype of a tool that should provide fast quantitative answers to help decision-making on the suitability of implementing traffic restrictions during air pollution episodes. The model first solves the wind flow over the city streets ignoring vorticity and turbulence. The obtained velocity field is used to transport the pollutant via a semi-Lagrangian model, combining the particle finite element method of second generation (PFEM2) with the finite element method. A variable absorption term is used to account for the part of the contaminant entering and leaving the calculation plane. The NO2 emissions are estimated from the historical traffic data. The model has been tested during four air pollution episodes in the city of Barcelona (Spain), two in summer and two in winter. A comparison against experimental measurements has been performed at seven different locations throughout the city with promising results.