Numerical Modeling of Pollutant Dispersion from Different Lanes in Urban Street Canyons

In order to study the dispersion characteristics of vehicle exhaust from different traffic lanes and provide a possible approach to reduce the exposure of residents and pedestrians to vehicle exhaust in urban street canyons,the flow field and vehicle exhaust concentration field of a double-lane street canyon were investigated based on a two dimensional k-e model and species transport equation. The validity of the numerical model was confirmed using wind tunnel experimental results. The result shows that the pollutants released from windward lane are more easily dispersed out of the street canyon. Pollutants from different lanes accumulate on the leeward side,which makes the pollutant concentrations on the leeward side pavement five times higher those on the windward side. The pollutant distribution along the bottom of the street canyon is sensitive to the position of the lanes. The pollutant concentrations on the bottom of the leeward building and the same-side pavement clearly decrease,assuming that the lanes move to the middle of the street canyon. The pollutant concentrations on the windward side are not sensitive to the position of the lanes. The pollutant concentrations on the bottom of the windward building and the same-side pavement are nearly double when the lane be located in the field of minor vertex on the windward side. Locating the lanes in the middle of the street canyon and preferentially planting green belts along roadsides are possible approaches to increase pedestrian comfort,decrease pedestrian traffic-related pollutant exposure and improve air quality in crowded areas,for example entrances and lower floors of buildings,and stores facing the street.