Designing green walls to mitigate fine particulate pollution in an idealized urban environment

Green walls are pivotal for advancing sustainable urban development and can mitigate fine particulate pollution in urban areas if designed with advantageous planting strategies, suitable vegetation, and sufficient wall coverage. This study evaluates the efficiency of several green wall designs and distinguishes the relative contributions of aerodynamic and deposition processes of vegetation to fine particulate matter removal in urban areas using Computational Fluid Dynamics (CFD) simulations. The simulations modeled four planting schemes, four wall area coverages, and two vegetation parameters, leaf area density (LAD) and deposition velocity (V_d). The results revealed that the leeward planting scheme with LAD = 4 m²/m³, V_d = 0.05 m/s, and 100% wall area coverage was the most efficient green wall design, which reduced up to 50% of the fine particulate concentrations at the pedestrian level (2 m height) in the downstream street. In addition to the aerodynamic effect, this study found a substantial contribution from the deposition in alleviating fine particulate pollution. Based on our findings, leeward green walls with high deposition efficiencies are recommended, and a suitable LAD should be selected to prevent adverse effects on urban ventilation. These insights highlight the benefits of green walls for improving air quality and sustainable cities.