PREDICTION OF PARTICLE DISPERSION WITHIN A STREET CANYON BY COUPLED SIMULATION OF CHEMICAL REACTION, PARTICLE DYNAMICS, AND CFD

Abstract

In the urban environment, gas, such as nitrogen dioxide, and particles impose adverse impacts on pedestrians’ health. Conventional computational fluid dynamics (CFD) methods regarding particle as passive scalar cannot reproduce the formation of nitrogen dioxide and secondary aerosols thus leading to uncertain prediction. In this study, SSH-Aerosol, a modular box model that simulates the evolution of gas, primary and secondary aerosols, was coupled with the CFD software OpenFOAM. The transient dispersion of pollutants emitted from traffic in a street canyon was simulated using unsteady Reynolds-averaged Navier–Stokes equations (RANS) model. The simulated pollutant concentrations were validated from field measurements. We compared particle size distributions and chemical compositions between the coupled and the conventional models. The results show that dry deposition played the most important role in aerosol dynamics for particles with diameter larger than 0.4 μm, while coagulation largely influenced the size distribution of small particles. In addition, secondary aerosol formation affected the mass concentration of inorganic and organic matters.