Buoyant Effect to The Pollutants Transport in Street Canyons

• Main Authors: Lu, Cheng-Chung, 呂政忠
• Other Authors: Chen,Jyun-Chen Luke
• Format: Others
• Language: zh-TW
• Published: 1996
• Online Access: http://ndltd.ncl.edu.tw/handle/29043348645998535450

碩士 === 淡江大學 === 水資源及環境工程學系 === 84 === Carbon monoxide distribution in street canyons under various geometry''s,atmospheric stability, temperature gradient induced buoyant effect and trafficload were simulated. We intend to use the simulation results to evaluatepedestrian pollutant exposure and to provide external conditions forevaluating indoor air quality of the buildings beside urban street. In thisstudy, we consider several factors those may affect the pollutant distributionin street canyons. The considered factors include geometry of the streetcanyons, atmospheric stability, traffic load and turbulent buoyant effect. Atwo-dimensional domain that includes suburban roughness and urban streetcanyons was considered as the simulation domain. The considered influentialfactors were imposed into the simulation through the associated boundaryconditions. The simulated results show that serious pollutant accumulationoccurred at where double vortices encountered and the situation only occurredat specific aspect ratios of the street canyons. Usually, the stagnation zoneformed at where the encounter of two vortices that reduce the transport ofpollutant and the pollutant tent to accumulate at the region. Buoyant effectto the vortices formation was found that the double vortices occurred atsmaller aspect ratio of the canyons with buoyancy than those without buoyancy. The buoyant effect also change the pollutant transport pattern in the canyons.The pedestrian exposure to the street air pollutant under various trafficloads and atmospheric stability were evaluated. This study concluded that thepatterns of pollutant distribution in different street canyons are mostlyaffected by their aspect ratios where the affect of buoyancy and atmosphericstability played less role. The pedestrian exposure to the street airpollution is considered to be serious under specific conditions when pollutantconcentrations at 3 m above ground level are very high. Those specificconditions were also found in this study.