Atmospheric pollution threatens human health worldwide, with tropospheric ozone (O3) and particulate matter (PM) among the most harmful pollutants. Urban trees can reduce the concentration of air pollutants through dry deposition on their canopies and stomatal uptake. At the same time, urban trees can deteriorate air quality by emitting aerosol- and O3 precursors in the form of biogenic volatile organic compounds (BVOCs). O3 and PM removal, and BVOC emissions vary depending on the tree species. Therefore, the diversity and spatial distribution of urban trees significantly influence their impact on local air quality. This study employs a dual approach to assess and map the impact of urban trees on air quality in Geneva, Switzerland. Firstly, we use the i-Tree Eco model combined with a tree inventory (237,191 trees) to quantify BVOC emissions and PM10 (PM < 10 µm) and O3 removal at the genus level. Secondly, we develop a species-level parameterization using 51 common urban tree species to estimate the same variables and ozone-forming potential (OFP). Results show that the tree density is heterogeneous in the study area, leading to neighborhoods with greater biomass and, therefore, stronger influence by trees on local air quality. According to i-Tree Eco, urban trees in Geneva emitted 50 t of BVOCs, while removing 14 t of PM10 and 52 t of O3 in 2014. With the species-level parametrization, we estimate that urban trees removed about 66 ± 55 t of PM10 and 150 ± 96 t of O3 in 2014. However, they could also emit about 130 ± 52 t of BVOCs annually, which, under favorable conditions, can form 1153 ± 519 t of O3. Depending on the method, urban trees removed between 4 and 19 % of the anthropogenic PM10 emissions. The annual removal rates are comparable to findings in other European cities. The disparities between the two approaches are due to different parameterizations. This study could help urban planners to select adequate species for future planting programs in Geneva and more generally. It showed that the impact of urban trees on air quality is spatially heterogeneous but significant, and tightly linked to the species composition.

中文翻译：

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量化城市树木对瑞士日内瓦空气质量的影响


大气污染威胁着全世界的人类健康，其中对流层臭氧 （O3） 和颗粒物 （PM） 是最有害的污染物。城市树木可以通过树冠上的干燥沉积和气孔吸收来降低空气污染物的浓度。同时，城市树木会以生物挥发性有机化合物 （BVOC） 的形式排放气溶胶和 O3 前体，从而恶化空气质量。O3 和 PM 去除以及 BVOC 排放因树种而异。因此，城市树木的多样性和空间分布显著影响其对当地空气质量的影响。本研究采用双重方法来评估和绘制城市树木对瑞士日内瓦空气质量的影响。首先，我们使用 i-Tree Eco 模型结合树木清单（237,191 棵树）来量化 BVOC 排放和 PM10（PM < 10 μm）和 O3 在属水平上的去除。其次，我们使用 51 种常见的城市树种开发了物种水平参数化，以估计相同的变量和臭氧形成潜力 （OFP）。结果表明，研究区域的树木密度是异质的，导致社区具有更大的生物量，因此树木对当地空气质量的影响更大。根据 i-Tree Eco 的数据，2014 年日内瓦的城市树木排放了 50 吨 BVOC，同时去除了 14 吨 PM10 和 52 吨 O3。通过物种水平参数化，我们估计 2014 年城市树木去除了约 66 ± 55 t PM10 和 150 ± 96 t O3。然而，它们每年也可能排放约 130 ± 52 吨 BVOC，在有利条件下，可以形成 1153 ± 519 吨 O3。根据方法的不同，城市树木去除了 4% 到 19% 的人为 PM10 排放物。 年移除率与其他欧洲城市的调查结果相当。两种方法之间的差异是由于参数化不同造成的。这项研究可以帮助城市规划者为日内瓦和更普遍的未来种植计划选择合适的树种。结果表明，城市树木对空气质量的影响在空间上是异质的，但很重要，并且与物种组成密切相关。