Pollutant removal, dispersion, and entrainment over two-dimensional idealized street canyons

Abstract

Idealized two-dimensional (2D) street canyon models of unity building-height-to-street-width (aspect) ratio are employed to examine the pollutant transport over hypothetical urban areas. The results show that the pollutant removal is mainly governed by atmospheric turbulence when pollutant sources exist in the street canyons. Numerous decelerating, uprising air masses are located at the roof level, implying that the pollutant is removed from the street canyons to the urban boundary layer (UBL) by ejections. For the street canyons without pollutant source, the removal by ejections is limited leading to insignificant turbulent pollutant removal. The roof-level turbulent kinetic energy (TKE) distribution demonstrates that its production is not governed by local wind shear but the descending TKE from the UBL. In the UBL, the pollutant disperses rapidly over the buildings, exhibiting a Gaussian-plume shape. The vertical pollutant profiles illustrate a self-similarity behavior in the downstream region. Future studies will be focused on the characteristic plume shape over 2D idealized street canyons of different aspect ratios.