Vegetation Planting Design Influences PM_2.5 Transport and Distribution in Urban Open-Road Environments

Traffic emissions contribute to fine particulate matter (PM2.5) exposure near roads. Vegetation barriers (VBs) alter particle transport, but their effects depend on planting design and local airflow. This study simulated 24 planting and wind-speed scenarios for a roadside VB and a downwind building in Shanghai. Vegetation was represented by aerodynamic resistance; foliage deposition was not modelled. Field comparison used 40 locations at 1.5 m, separate from five road-edge locations used for inlet prescription. At a reference wind speed of 2.0 m/s, tree-dominated VBs had 10.52% higher mean concentrations within the barrier than shrub-dominated VBs (33.95 versus 30.72 µg/m³). Mean sidewalk concentrations across vegetated configurations were 14.48% higher than in the vegetation-free control. Along the sampled façade profile from 1.5 to 19.5 m, tree-dominated VBs had lower mean concentrations than the control (28.42 versus 29.47 µg/m³), whereas shrub-dominated VBs had higher concentrations (31.09 µg/m³). Increasing reference wind speed from 1 to 5 m/s decreased mean concentrations within the all-tree VB and along the façade. These results describe simulated concentration redistribution under the prescribed inflow and geometry. Predictions above 1.5 m remain unevaluated, and unquantified mesh sensitivity limits interpretation of small differences among planting arrangements.