Greenery strategies for reducing pedestrian particulate exposure along an open-flanked urban arterial road

Despite extensive research on the role of roadside greenery in traffic pollution mitigation, its effectiveness remains debated due to limited understanding of pollutant dispersion and deposition near green barriers. This study addresses the gap by combining field measurements of PM_2.5, PM₁₀, and black carbon (BC) along an open-flanked urban arterial road with ENVI-met simulations integrating dynamic traffic emissions to evaluate the impact of greening arrangements on particle dynamics under varying wind conditions. Measurement results reveal distance-dependent particulate attenuation within 10 m of roadways, with BC showing the highest greenbelt-induced reduction (15.5–30.5 %), surpassing PM_2.5 and PM₁₀ (0.5–5.5 %). Poor roadside ventilation exacerbates pedestrian-level accumulation under complex vegetation. Numerical modeling further confirms that only multi-layered tree arrangements—optimized for spacing, leaf area index, and crown shape to suit local conditions—optimize sidewalk particle reduction through enhanced dispersion-deposition synergy despite size-dependent deposition hierarchy (PM₁₀ > BC > PM_2.5). Narrow-spaced plantings (3 m) with spherical canopies maximize turbulent deposition, while excessive leaf area index induces stagnation. Perpendicular winds drive velocity-dependent deposition, with BC exhibiting greatest wind-speed sensitivity above 3 m/s. PM₁₀ deposits fastest, whereas near-stagnant conditions (0.05 m/s) promote PM_2.5 accumulation at BC-comparable rates. Moderate winds (1–3 m/s) optimize phytofiltration by balancing capture and retention. The results establish that strategically designed multi-layered vegetation, tailored to local aerodynamic conditions and tree morphology, effectively reduces pedestrian exposure to traffic particulates, informing urban green infrastructure policies.