Pollutant dispersion over two–dimensional idealised urban roughness: a large–eddy simulation approach
A series of two–dimensional (2D) street canyon models with a wide range of building–height–to–street–width (aspect) ratios are employed in this study to elucidate the pollutant transport over idealised urban areas. The large–eddy simulation (LES) is used to resolve the turbulent flows and pollutant transport in the urban boundary layer (UBL) over the street canyons. The results show that the pollutant removal is governed by atmospheric turbulence in both skimming flow and wake interference regimes. In the UBL, the vertical pollutant profiles illustrate self–similarity behaviours in the downstream region. The pollutant disperses rapidly over the buildings, exhibiting a Gaussian–plume shape. The maximum vertical pollutant dispersion coefficient is observed at aspect ratio equal to 1/10. A strong correlation between friction factor and dispersion coefficient is revealed, implying that the downstream air quality could be improved by increasing the roughness of urban areas.
Keywords: large–eddy simulation, LES, urban roughness, urban street canyons, pollutant dispersion, air pollution, air quality, atmospheric dispersion modelling, pollutant transport, turbulent flow, friction, atmospheric turbulence, skimming flow, wake interference