Assessing the efficacy of green walls versus street green lanes in mitigating air pollution: A critical evaluation

Urban green spaces, particularly street trees and greenways, are increasingly recognized as tools for mitigating air pollution. However, their effectiveness can vary depending on their configuration and urban canyon geometry. This study, aimed at providing practical solutions, assessed the impact of different green space configurations, including street trees, green lanes, green walls, and hedges, on particulate matter (PM) concentrations within urban canyons of varying aspect ratios by employing environmental simulations and wind tunnel tests performed in ENVI-met software. Results demonstrate that green walls significantly outperform street trees in reducing PM concentrations by up to 43%, attributing this to reduced air flow disruption. Green walls also create a more uniform PM distribution within canyons, decreasing concentration differences by 31% compared to green (tree) lanes. Conversely, dense tree lanes exacerbate PM deposition due to wind flow interference. These findings suggest that incorporating green walls into urban design can be a highly effective strategy for improving air quality within densely built environments. • Green Walls' effect on PMs pollution is less dependent on urban canyon ratios changes. • Green Walls have been effective up to 43% on PMs air pollution compared to Trees lane. • Green Walls' efficiency on control PMs pollution rises on higher urban canyon ratios. • Dense trees near traffic lead to the deposition of air pollution in Urban Canyons.