Numerical modelling of the passive control of air pollution in asymmetrical urban street canyons using refined mesh discretization schemes

Numerical modelling of the passive control of air pollution in asymmetrical urban street canyons using refined mesh discretization schemes, This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Abstract 10 This study evaluates the potential of passive controls in asymmetrical street canyons to reduce 11 personal exposure to air pollutants on footpaths. A passive control in the form of a low boundary 12 wall (LBW) may act as a baffle within a street canyon, producing modified airflow patterns and 13 increase pollutant dispersion at street level. This numerical modelling study assessed the spatial 14 distribution of concentrations of a tracer pollutant in a street canyon. Concentrations were measured 15 along the centre of both footpaths at breathing height to determine the percentage difference 16 between pollutant concentrations in canyons with and without passive controls. The investigation 17 assessed asymmetrical street canyons of different building height ratios (H 1 /H 2 ratio ranging from 18 0.5–1.5 in 0.1 intervals) in perpendicular wind conditions. The results indicated that the H 1 /H 2 ratio 19 affects pollutant dispersion and the implementation of a passive control can reduce the pollutant 20 concentration on the footpaths. The percentage difference in concentrations induced by the presence 21 of footpath LBWs ranged from an increase of up to 19% to a reduction of 30% on the leeward 22 footpath, with reductions between 26% and 50% on the windward footpath with varying H 1 /H 2 23 ratios. Comparing the results to a central LBW configuration identified the creation of two distinct 2 vortices in the street canyon. The results also identified the effect of wind speed on the development 1 of primary vortices. For urban planners, passive controls offer a method of increasing dispersion by 2 modifying normal air flow patterns and potentially improve air quality in urban street canyons.