School of Energy and Environment, City University of Hong Kong, Hong Kong, China.
School of Energy and Environment, City University of Hong Kong, Hong Kong, China; Guy Carpenter Climate Change Centre, City University of Hong Kong, Hong Kong, China.
J Environ Manage. 2019 Oct 15;248:109304. doi: 10.1016/j.jenvman.2019.109304. Epub 2019 Jul 29.
Trees offer a range of ecosystem services and remain important in providing human benefits. However, emerging literature questions the long-accepted view of trees being able to improve air quality in urban parks. The aerodynamic effect of trees was identified as a major reason for the change of pollutant distribution in near-road parks, where trees can act as porous barriers and cause localised concentration increase. Although not yet fully developed, planting strategies aiming to mitigate the negative effect of vegetation on air quality should be encouraged in future park design. In this study, we explored the effect of tree planting design on pollutant diffusion by integrating field surveys in urban parks in Hong Kong with computational fluid dynamic (CFD) modelling. A series of indicators associated with tree morphology and landscape were derived from the surveys and their influence on air pollutant distribution in parks was examined using ENVI-MET. Dense trees with low crown base were found effective in improving air quality within parks when planted as barriers with a width of ~15 m at borders. However, more extensive planting led to a decrease in wind velocity and an increase in pollutant concentrations, which should be avoided. Tall trees tended to have little influence on airflow at the pedestrian level, which means they seem appropriate for small urban parks where wide barriers are not applicable and rapid ventilation should be encouraged. The tree distribution also altered the airflow and pollutant dispersion in parks. Our study provides clues for thoughtful planting strategies which can optimise air quality in urban parks.
树木提供了一系列生态系统服务，在提供人类效益方面仍然很重要。然而，新兴文献质疑树木能够改善城市公园空气质量的长期公认观点。树木的空气动力效应被认为是导致近路公园中污染物分布变化的主要原因，在这些公园中，树木可以作为多孔屏障，并导致局部浓度增加。尽管尚未完全发展，但在未来的公园设计中，应鼓励采取种植策略来减轻植被对空气质量的负面影响。在这项研究中，我们通过整合香港城市公园的实地调查和计算流体动力学 (CFD) 模型，探讨了植树设计对污染物扩散的影响。从调查中得出了一系列与树木形态和景观相关的指标，并使用 ENVI-MET 检查了它们对公园内空气污染物分布的影响。当种植在边界处宽度约为 15m 的障碍物时，具有低冠基的茂密树木被发现可以有效地改善公园内的空气质量。然而，更广泛的种植会导致风速降低和污染物浓度增加，这是应该避免的。高大的树木往往对行人高度的气流影响不大，这意味着它们适合于不适用宽屏障且应鼓励快速通风的小型城市公园。树木的分布也改变了公园内的气流和污染物扩散。我们的研究为深思熟虑的种植策略提供了线索，这些策略可以优化城市公园的空气质量。
