Fry Juliane L, Ooms Pascale, Krol Maarten, Kerckhoffs Jules, Vermeulen Roel, Wesseling Joost, van den Elshout Sef
Meteorology and Air Quality (MAQ), Environmental Sciences Group, Wageningen University 6708PB Wageningen the Netherlands
Institute for Marine and Atmospheric Research (IMAU), Utrecht University 3584 CC Utrecht the Netherlands.
Environ Sci Atmos. 2025 Feb 6;5(3):394-404. doi: 10.1039/d4ea00157e. eCollection 2025 Mar 13.
Urban street trees can affect air pollutant concentrations by reducing ventilation rates in polluted street canyons (increasing concentrations), or by providing surface area for deposition (decreasing concentrations). This paper examines these effects in Rotterdam, the Netherlands, using mobile measurements of nitrogen dioxide (NO), particulate matter (PM), black carbon (BC), and ultrafine particulate matter (UFP). The effect of trees is accounted for in regulatory dispersion models (https://www.cimlk.nl) by the application of an empirically determined tree factor, dependent on the existence and density of the tree canopy, to concentrations due to traffic emissions. Here, we examine the effect of street trees on different pollutants using street-level mobile measurements in a detailed case study (repeated measurements of several neighboring streets) and a larger statistical analysis of measurements across the urban core of Rotterdam. We find that in the summertime, when trees are fully leafed-out, the major short-lived traffic-related pollutants of NO and BC have higher concentrations in streets with higher traffic and greater tree cover, while PM has slightly lower concentrations in streets with higher tree factor. UFP shows a less clear, but decreasing trend with tree factor. In low-traffic streets and in wintertime (fewer leaves on trees) measurements confirm the importance of leaves to pollutant trapping by trees, by finding no enhancement of NO and BC with increasing tree cover, rather a slightly decreasing trend in pollutant concentrations with tree factor. Our observations are consistent with the dominant effect of (leafed-out) trees being to trap traffic-emitted pollutants at the surface, but that PM in street canyons is more often added by transport from outside the street, which can be attenuated by tree cover. Overall, these measurements emphasize that both traffic-emitted and regional sources are important factors that determine air quality in Rotterdam streets, making the effect of street trees different for different pollutants and different seasons.
城市街道树木可通过降低污染街道峡谷中的通风率（增加污染物浓度），或通过提供污染物沉降的表面积（降低污染物浓度）来影响空气污染物浓度。本文利用对二氧化氮（NO）、颗粒物（PM）、黑碳（BC）和超细颗粒物（UFP）的移动测量，研究了荷兰鹿特丹的这些影响。通过应用一个根据树冠的存在和密度经验确定的树木因子，在监管扩散模型（https://www.cimlk.nl）中考虑树木对交通排放导致的污染物浓度的影响。在此，我们通过一个详细的案例研究（对几条相邻街道的重复测量）以及对鹿特丹城市核心区域测量数据的更大规模统计分析，研究街道树木对不同污染物的影响。我们发现，在夏季树木枝叶繁茂时，交通相关的主要短期污染物NO和BC在交通流量较大且树木覆盖率较高的街道中浓度较高，而PM在树木因子较高的街道中浓度略低。UFP的趋势不太明显，但随着树木因子的增加呈下降趋势。在交通流量较小的街道和冬季（树木叶子较少）的测量结果证实，树叶对树木捕获污染物很重要，因为随着树木覆盖率增加，NO和BC没有增加，而是污染物浓度随树木因子略有下降趋势。我们的观察结果与（枝叶繁茂的）树木的主要作用是在地表捕获交通排放的污染物一致，但街道峡谷中的PM更多是由街道外的传输添加的，而树木覆盖可以减弱这种传输。总体而言，这些测量结果强调，交通排放源和区域源都是决定鹿特丹街道空气质量的重要因素，使得街道树木对不同污染物和不同季节的影响有所不同。
