Built-up environments limit air pollution dispersion in street canyons and lead to complex trade-offs between green infrastructure (GI) usage and its potential to reduce near-road exposure. This study evaluated the effects of an evergreen hedge on the distribution of particulate matter (PM₁, PM_2.5, PM₁₀), black carbon (BC) and particle number concentrations (PNCs) in a street canyon in West London. Instrumentation was deployed around the hedge at 13 fixed locations to assess the impact of the hedge on vertical and horizontal concentration distributions. Changes in concentrations behind the hedge were measured with reference to the corresponding sampling point in front of the hedge for all sets of measurements. Results showed a significant reduction in vertical concentrations between 1 and 1.7 m height, with maximum reductions of –16% (PM₁ and PM₁₀) and –17% (PM_2.5) at ∼1 m height. Horizontal concentrations revealed two zones between the building façade and the hedge, with opposite trends: (i) close to hedge (within 0.2 m), where a reduction of PM₁ and PM_2.5 was observed, possibly due to dilution, deposition and the barrier effect; and (ii) 0.2–3 m from the hedge, showing an increase of 13–37% (PM₁) and 7–21% (PM_2.5), possibly due to the blockage effect of the building, restricting dispersion. BC showed a significant reduction at breathing height (1.5 m) of between –7 and –50%, followed by –15% for PNCs in the 0.02–1 µm size range. The ELPI + analyser showed a peak of ∼30 nm. The presence of the hedge led to a ∼39 ± 32% decrease in total PNCs (0.006–10 µm), suggesting a greater removal in different modes, such as a 83 ± 12% reduction in nucleation mode (0.006–0.030 µm), 74 ± 15% in ultrafine (≤0.1 µm), and 34 ± 30% in accumulation mode (0.03–0.3 µm). These findings indicate graded filtering of particles by GI in a near-road street canyon environment. This insight will guide the improved design of GI barriers and the validation of microscale dispersion models.

建成环境限制了街道峡谷中的空气污染扩散，并导致在绿色基础设施 (GI) 的使用与其减少道路附近暴露的潜力之间进行复杂的权衡。本研究评估了常绿树篱对颗粒物分布的影响（PM ₁、 PM _2.5、 PM ₁₀)、黑碳 (BC) 和粒子数浓度 (PNC) 在伦敦西部的一个街道峡谷中。在 13 个固定位置的对冲周围部署了仪器，以评估对冲对垂直和水平浓度分布的影响。套期后的浓度变化是参照套期前的相应采样点测量的。结果表明，在 1 到 1.7 m 高度之间，垂直浓度显着降低，在 ∼1 m 高度处最大降低了 –16%（PM ₁和 PM ₁₀）和 –17%（PM _2.5）。水平浓度显示了建筑立面和树篱之间的两个区域，趋势相反：（i）靠近树篱（0.2 m 内），PM 减少₁和 PM _2.5被观察到，可能是由于稀释、沉积和阻隔效应；(ii) 距离对冲 0.2–3 m，显示增加 13–37% (PM ₁ ) 和 7–21% (PM _2.5)，可能是由于建筑物的阻塞效应，限制了分散。BC 显示呼吸高度 (1.5 m) 显着降低，介于 –7 和 –50% 之间，其次是 0.02–1 µm 尺寸范围内的 PNCs –15%。ELPI + 分析仪显示约 30 nm 的峰值。对冲的存在导致总 PNC 减少了 ∼39 ± 32% (0.006-10 µm)，这表明在不同模式下去除率更高，例如成核模式 (0.006-0.030 µm) 减少了 83 ± 12%，超细 (≤0.1 µm) 为 74 ± 15%，累积模式 (0.03–0.3 µm) 为 34 ± 30%。这些发现表明，在道路附近的街道峡谷环境中，GI 对粒子的分级过滤。这一见解将指导改进 GI 屏障的设计和验证微尺度弥散模型。