Abstract
As a green infrastructure component, urban street vegetation is increasingly being utilized to mitigate air pollution, control microclimates, and provide aesthetic and ecological benefits. This study investigated the effect of vegetation configurations on particulate matter (PM) flows for pedestrians in road traffic environments via a computation fluid dynamics analysis based on the road width (four and eight-lane) and vegetation configuration (single-, multi-layer planting, and vegetation barrier). Airflow changes due to vegetation influenced PM inflow into the sidewalk. Vegetation between roadways and sidewalks were effective at reducing PM concentrations. Compared to single-layer planting (trees only), planting structures capable of separating sidewalk and roadway airflows, such as a multi-layer planting vegetation barrier (trees and shrubs), were more effective at minimizing PM on the sidewalk; for wider roads, a multi-layer structure was the most effective. Furthermore, along a four-lane road, the appropriate vegetation volume and width for reducing PM based on the breathing height (1.5 m) were 0.6 m3 and 0.4 m, respectively. The appropriate vegetation volume and width around eight-lane roads, were 1.2–1.4 m3 and 0.8–0.93 m, respectively. The results of this study can provide appropriate standards for street vegetation design to reduce PM concentrations along sidewalks.
Highlights
Road traffic emissions containing particulate matter (PM) and gaseous pollutants, such as carbon monoxide (CO) and nitrogen oxides (NOx), are a primary source of air pollution [1,2,3,4]
In the F1 model, where only trees were planted on a four-lane road, the flow encountering the leeward wall passed between the crown and ground, thereby increasing the velocity (Figure 3a)
The PM concentration along the leeward sidewalk may have differed from the overall concentration of the entire atmosphere
Summary
Road traffic emissions containing particulate matter (PM) and gaseous pollutants, such as carbon monoxide (CO) and nitrogen oxides (NOx), are a primary source of air pollution [1,2,3,4]. Research has demonstrated that vegetation impacts local air quality through aerodynamic and deposition pathways [11]. The pollutant concentrations behind vegetation or physical barriers can be mitigated through deposition and vertical mixing; reducing convection and turbulence via the windbreak effect improves the air quality behind roadside vegetation significantly [12,14,21,22,23]. Urban vegetation can positively affect air quality, microclimate control, carbon fixation, rainwater drainage, and noise pollution [24,25,26,27,28], and promotes biodiversity by providing food sources, habitats, and landscape connectivity for urban fauna [29,30,31]. Green spaces in urban environments connect community dwellers, encourage physical activity, reduce stress, and are excellent recreational spaces [32,33]
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