Effect of trees on air pollutant dispersion inside intra-urban roads

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Effect of trees on air pollutant dispersion inside intra-urban roads


Author: Ho, Ming-sang
Title: Effect of trees on air pollutant dispersion inside intra-urban roads
Degree: M.Eng.
Year: 2011
Subject: Air -- Pollution.
Trees -- Effect of air pollution on.
Air flow -- Mathematical models.
Roadside improvement.
City planning -- Environmental aspects.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Building Services Engineering
Pages: ix, 96 leaves : ill. (some col.) ; 30 cm.
InnoPac Record: http://library.polyu.edu.hk/record=b2449798
URI: http://theses.lib.polyu.edu.hk/handle/200/6247
Abstract: A field study of pollutant dispersion under the aerodynamic effects of trees in an idealized urban street canyon was undertaken. The local scale flow and pollutant concentration were analyzed by field measurement and numerical modeling - Computational Fluid Dynamics (CFD). The field measurement was performed in a neighborhood scale in proximity of two complex urban junctions formed by street canyons of similar aspect ratios with and without tree-planting. It is aiming to examine the local pollutant concentration level and dispersion under the combined influence of building configuration and vegetation. The street-level pollutant concentrations were measured at the facade of the street canyons and the measurement results show that trees contribute to hinder the pollutant dispersion as welt as the increase of pollutant concentration level. The CFD simulation is using the standard k-{464} turbulence model with a Reynolds Stress turbulence closure for flow and the advection-diffusion method for concentration calculation which included in the commercial suite FLUENT TM. The numerical modeling of avenue-like tree planting in an idealized street canyon was undertaken. With the aspect ratio W/H=2 (the ratio of the building height, H to the street width, W) and perpendicular approaching wind direction. The pollutant concentration field (carbon monoxide, CO) obtained from model simulations have been compared with the wind tunnel experimental data (CODAS, 2008) for the model validation. These analyses are used as reference modeling study for the extension of building design consideration in a tree-planting street canyon. Building's setback and separation are the most common building's configures modification in urban design. Therefore. CFD simulations for various building shape with the presence of trees were performed to study the flow field and the pollutant concentration distribution under the aerodynamic effect of trees. It shows that both setback and separation can reduce the pollutant concentration inside the canyon zone about 20% and 40% respectively compare with the original model. And this effect can be maximized in larger aspect ratio. This study uses an appropriate CFD modeling methodology to investigate the aerodynamic effects of trees in street canyons hence provides references for the arrangement of building and vegetation in the urban environment with regard to air quality issue.

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