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Focusing on the effect of street morphology on the ventilation efficiency, this paper presents 3D computational fluid dynamics (CFD) simulations of airflow and pollutant dispersion within urban-like three-way intersections, four-way intersections and roundabouts. The steady-state Reynolds-averaged Navier-Stokes (RANS) k-ε turbulence model is adopted and eight directions of the approaching wind are considered. The ventilation efficiency is evaluated using the ventilation indices purging flow rate (PFR) and the net escape velocity (NEV). Results show the sensitivity of the ventilation efficiency to the type of intersection, to the wind direction and to the number of branches. Specifically, the ventilation efficiency of the investigated three-way intersections is found to be better than that of the other intersections, especially when the angle between the streets is large, while that of roundabouts is also considerable, even with a similar average wind velocity, among the cases evaluated in this paper. Further, the influence of the wind direction for the three-way and four-way intersections is greater than that on roundabouts. Studies on the ventilation efficiency at urban intersections are not common in the literature and this work may help urban planners to better design such hub nodes of urban traffic, where traffic-related pollutants are not easily dispersed, thus avoiding harm to the health of pedestrians and surrounding residents.

To improve ventilation efficiency and reduce pollution concentration in urban spaces, eco-strategies, including greening, have been suggested. However, there is still very little evidence to assert the benefits of such greening options, particularly at urban street intersections. Therefore, in this work, air flow and pollutant dispersion within urban-like three-way, four-way, and roundabouts intersections are investigated with three simple and five combined greening layouts. Three-dimensional computational fluid dynamics (CFD) analysis using the Reynolds-averaged Navier–Stokes model was conducted considering multiple wind directions. The ventilation efficiency was evaluated using the ventilation indices purging flow rate (PFR) and net escape velocity (NEV). The investigation of simple greening layouts shows that shrubs alone may enhance increase ventilation (i.e., increase PFR and NEV), and trees could increase the pollutant concentration at the pedestrian level. A comparison of greening layouts combining trees and shrubs shows that the presence of greening reduces ventilation and worsens the pollution condition at street intersections, except for shrubs located in the central zone within roundabouts. Specifically, NEV decreases by 16%–43% at four-way and three-way intersections owing to the presence of greening. Greening layouts with two rows of trees located 2.2 m away from buildings show overall significant negative effects on ventilation, particularly for wind directions ϕ = 0°, 45°, and 90°. The impact of shrubs and trees on ventilation at the roundabout is less significant, with NEV varying by 4%–11%.