Influence of trees on the pollutant concentrations in urban street canyon-numerical simulation

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Influence of trees on the pollutant concentrations in urban street canyon-numerical simulation

 

Author: Lu, Feifei
Title: Influence of trees on the pollutant concentrations in urban street canyon-numerical simulation
Degree: M.Eng.
Year: 2013
Subject: Trees -- Effect of air pollution on.
Air -- Pollution.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Building Services Engineering
Pages: viii, 69 leaves : ill. (some col) ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2641111
URI: http://theses.lib.polyu.edu.hk/handle/200/7109
Abstract: The microclimate of urban street canyon has drawn the attention of public and city planners. Planting trees in street canyon is a way to mitigate the urban heat island (UHI) effect. However, trees act as obstacles to prevent the fresh air flowing into street canyon thus the traffic-related pollutant increases. This study examined a street canyon of Aspect Ratio 1 (AR1) with perpendicular prevailing wind which is the worst situation. The simulation was conducted by ANSYS FLUENT 13.0 software with the standard k-{464} turbulence model. Trees were simulated as the source term. A line source lied in the bottom of canyon was applied to simulate the traffic exhaust emissions. The street canyon with and without trees were modeled. Trees were positioned in a line at the center axis of street canyon, varying crown size, leaf area density (LAD) and tree planting density with three different wind speed (4.7m/s, 2.5m/s and 1.5m/s). CO concentrations were measured at the facades and pedestrian level (1.5m height) in the street canyon. Increasing tree crown size, LAD and tree planting density led to rising CO concentrations at leeward side while the concentration of windward side was reduced. Trees are not supposed to occupy much volume of the street canyon thus they will not affect the air exchange which could reduce the mean pollutant levels.

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