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Abstract

Air pollution in big city areas resulting from exhaust emissions is a major urban problem. Often traffic pollution excess controls air pollution management decisions. There are a number of elaborate predictive models of pollutant dispersion and diffusion that address the effects of variable shapes of city buildings on pollutant concentrations, but few are fully validated. This study presents ventilation behavior in different street canyon configurations. To evaluate dispersion in a model urban street canyon, a series of tests with various street canyons with different height in upwind and downwind of street canyon are presented. These buildings were arranged in 2-D configurations with different height in upwind and downwind of street canyon. The results showed that a higher concentration of pollutants accumulates under the leeward of the street canyon due to the occurrence of a clockwise vortex inside the street canyon when the street canyon aspect ratio (B/H) is 2. On the contrary, over the windward of the street canyon, a lower concentration of pollutants accumulates due to the occurrence of an anti-clockwise vortex. The flow and dispersion of gases emitted by a line source located between two buildings inside of the urban street canyons were also determined by numerical model. Calculations were compared against CFD prediction in an Environmental Wind Tunnel of Wind Engineering Center at Tamkang University.

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