Sheikh H A, Maher B A, Woods A W, Tung P Y, Harrison R J
Department of Earth Sciences, University of Cambridge, Downing Site, CB2 3EQ, UK.
Center for Environmental Magnetism and Palaeomagnetism, University of Lancaster, LA1 4YQ, UK.
Sci Total Environ. 2023 Dec 10;903:166598. doi: 10.1016/j.scitotenv.2023.166598. Epub 2023 Aug 25.
One aim of roadside green infrastructure (GI) is to mitigate exposure to local, traffic-generated pollutants. Here, we determine the efficacy of roadside GI in improving local air quality through the deposition and/or dispersion of airborne particulate matter (PM). PM was collected on both pumped air filters and on the leaves of a recently installed 'tredge' (trees managed as a head-high hedge) at an open road environment next to a primary school in Manchester, U.K. The magnetic properties of PM deposited on leaves and filters (size fractions PM and PM) were deduced from hysteresis loops, first-order reversal curves (FORCs), and low-temperature remanence measurements. These were complemented with electron microscopy to identify changes in magnetic PM concentration downwind of the tredge/GI. We show that the tredge is permeable to airflow using a simple CO tracer experiment; hence, it allows interception and subsequent deposition of PM on its leaves. Magnetic loadings per m of air from filters (PM saturation magnetisation, M, at 5 K) were reduced by 40 % behind the tredge and a further 63 % in the playground; a total reduction of 78 % compared to roadside air. For the PM fraction, the reduction in magnetic loading behind the tredge was remarkable (82 %), reflecting efficient diffusional capture of sub-5 nm Fe-oxide particles by the tredge. Some direct mixing of roadside and playground air occurs at the back of the playground, caused by air flow over, and/or through gaps in, the slowly-permeable tredge. The magnetic loading on tredge leaves increased over successive days, capturing ~23 % of local, traffic-derived PM. Using a heuristic two-dimensional turbulent mixing model, we assess the limited dispersion of PM < 22.5 μm induced by eddies in the tredge wake. This study demonstrates that PM deposition on leaves reduces exposure significantly in this school playground setting; hence, providing a cost-effective mitigation strategy.
路边绿色基础设施（GI）的一个目标是减轻对当地交通产生的污染物的暴露。在此，我们通过空气中颗粒物（PM）的沉积和/或扩散来确定路边绿色基础设施在改善当地空气质量方面的功效。在英国曼彻斯特一所小学旁的开放道路环境中，在抽气式空气过滤器以及最近安装的“树篱”（作为齐头高树篱管理的树木）的叶子上收集了PM。从磁滞回线、一阶反转曲线（FORCs）和低温剩磁测量中推导出沉积在叶子和过滤器上的PM（粒径分级为PM和PM）的磁性特性。这些通过电子显微镜进行补充，以识别树篱/绿色基础设施下风处磁性PM浓度的变化。我们通过一个简单的CO示踪实验表明树篱对气流是可渗透的；因此，它允许拦截并随后在其叶子上沉积PM。来自过滤器的每立方米空气中的磁负荷（5 K时的PM饱和磁化强度，M）在树篱后方降低了40%，在操场中进一步降低了63%；与路边空气相比，总共降低了78%。对于PM部分，树篱后方磁负荷的降低非常显著（82%），这反映了树篱对小于5 nm的铁氧化物颗粒的有效扩散捕获。操场后部会发生路边空气和操场空气的一些直接混合，这是由气流越过和/或穿过渗透性较差的树篱中的间隙引起的。树篱叶子上的磁负荷在连续几天内增加，捕获了约23%的当地交通源PM。使用一个启发式二维湍流混合模型，我们评估了树篱尾流中涡旋引起的小于22.5μm的PM的有限扩散。这项研究表明，在这个学校操场环境中，PM沉积在叶子上显著降低了暴露；因此，提供了一种具有成本效益的缓解策略。
