Numerical Simulation and In Situ Investigation of Fine Particle Dispersion in an Actual Deep Street Canyon in Hong Kong

Abstract

This paper reports a computational fluid dynamics simulation of airflow and fine particle (PM 2.5 ) dispersion in the street canyon in Hong Kong, using large eddy simulation. An aspect ratio (AR) of 2.7 and a Reynolds number of 5 Â 10 6 with a one main vortex, were used. This study focused mainly on the vehicle-induced momentum source and PM 2.5 concentrations were measured at 10 altitudes near the leeward wall in the street canyon, to provide high resolution measurements for model validation. The simulated PM 2.5 concentrations agreed well with the measurements, (R ¼ 0.85). The concentration was higher at the lower part near the leeward wall than the upper part.Higher concentration was found near the roof level. A near-uniform vertical dispersion of PM 2.5 near the windward wall was demonstrated; and the average concentrations were lower than found near the leeward wall. The intermittent escape of the PM 2.5 above the canyon at the roof level occurred mainly at the centre and near windward wall areas. The results demonstrated that a reduction in the AR can be conducive to pollutant dispersion in street canyon planning. The findings of this research would inform building designers to formulate effective strategies such as positioning of ventilation air intake, for the control of ingress of PM 2.5 into building environments.

Large Eddy Simulation of Vehicle Induced Turbulence in an Urban Street Canyon with a New Dynamically Vehicle-Tracking Scheme

“…The time step in simulations was 0.03s. A self-produced CFD cord was used in our current simulations, which was validated by our previous works (Gu et al, 2010;Zhang et al, 2011). The finite volume method was used to discretize the governing equations and the SIMPLE method was used to solve the discretized equations.…”

“…The drag force induced by moving vehicles was added to the additional source term of the governing equation (Zhang et al, 2011), as shown in Eq. (2).…”

“…The dispersion of fine particulates in a deep street canyon has been discussed previously (Zhang et al, 2011). Air recirculation inside a street canyon could hinder the outward transport of airborne pollutants, which could lead to poor air quality within an urban street canyon (Oke, 1988;Sharma and Khare, 2001;Xie et al, 2005).…”

Impact of Air Humidity Fluctuation on the Rise of PM Mass Concentration Based on the High-Resolution Monitoring Data

“…Meanwhile, the seriously high concentrations of PM 2.5 in ambient air is contributing to the ash haze weather in various cities (Friedlander and Marlow, 1977;Du et al, 2012). Various studies have shown that the mass concentration and chemical compositions of aerosols in each city are very different due to the different urban economic developments, traffic conditions, industrial activities and meteorological factors (Zhang et al, 2011;Zhang and Gu, 2013;Huang et al, 2014;Rohde and Muller, 2015), however, the characteristics of the atmospheric conditions on the formation of haze episodes have not been sufficiently studied.…”

Human settlement, civil engineering and silk road – Xi’an Jiaotong University, 120-year anniversary

“…Atmospheric pollution and urban air quality management: The study of urban air quality management and characterization of urban pollution [15][16][17] and emissions in urban areas and urban dispersion of pollution in street canyons to understand the behaviour of sources, dispersion and their chemical characteristics, [18][19][20] so as to develop urban air quality management strategies to provide guides for urban planning of city centres and urban architecture. 7,21 The development of simulation parameters for dispersion airflow of ambient air pollutants in urban environment is an important achievement for urban air quality management. 22,23 The triboelectric charging of airborne particles under various humidity conditions is a particular highlight of efforts to understand the possible mechanism for explosive growth of PM 2.5 concentration during pollution episode events that is frequently occurring in winter in China.…”