Numerical investigation of pollutant transport characteristics inside deep urban street canyons

• Published in: Atmospheric environment (1994) Vol. 43; no. 15; pp. 2410 - 2418
• Main Authors: Li, Xian-Xiang, Liu, Chun-Ho, Leung, Dennis Y.C.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.05.2009; Elsevier
• Subjects: Analysis methods; Applied sciences; Atmospheric pollution; Deep street canyon; Exact sciences and technology; Large-eddy simulation (LES); Pollutant dispersion; Pollutants physicochemistry study: properties, effects, reactions, transport and distribution; Pollution; Turbulent diffusion; Large-eddy simulation (LES); Pollutant dispersion; Turbulent diffusion; Deep street canyon; Pollutant behavior; Environmental factor; Urban area; Aspect ratio; Turbulent transport; Transport process; Street canyon; Large eddy simulation; Atmospheric boundary layer; Air pollution; Numerical simulation; Atmospheric dispersion; Boundary layer turbulence
• ISSN: 1352-2310; 1873-2844
• DOI: 10.1016/j.atmosenv.2009.02.022

A validated LES model was employed to simulate the street canyons of aspect ratio (AR) 3, 5, and 10. Three, five, and eight vertically aligned primary recirculations were found for the three cases, respectively, which showed decreasing strength with decreasing height. The ground-level wind speeds were found to be very small, making it extremely difficult for the ground-level pollutants to disperse. Local maxima of turbulence intensities were found at the interfaces between the primary recirculations and the shear layer. The pollutant trajectory followed the primary recirculations. High pollutant concentration and variance were found near the buildings where wind flowed upward. Large gradients of pollutant concentration and variance were also observed at the interfaces between the primary recirculations and the shear layer. Detailed analyses of concentration budget showed that the advection terms were responsible for pollutant redistribution within primary recirculations, while the turbulent transport terms were responsible for pollutant penetration between primary recirculations as well as pollutant removal from the street canyon.