This review updates a systematic review published in 2010 ( http://www.environmentalevidence.org/completed-reviews/how-effective-is-greening-of-urban-areas-in-reducing-human-exposure-to-ground-level-ozone-concentrations-uv-exposure-and-the-urban-heat-island-effect ) which addressed the question: How effective is ‘greening’ of urban areas in reducing human exposure to ground-level ozone concentrations, UV exposure and the ‘urban heat island effect’? Searches of multiple databases and journals for relevant published articles and grey literature were conducted. Organisational websites were searched for unpublished articles. Eligibility criteria were applied at title, abstract and full text and included studies were critically appraised. Consistency checks of these processes were undertaken. Pre-defined data items were extracted from included studies. Quantitative synthesis was performed through meta-analysis and narrative synthesis was undertaken. 308 studies were included in this review. Studies were spread across all continents and climate zones except polar but were mainly concentrated in Europe and temperate regions. Most studies reported on the impact of urban greening on temperature with fewer studies reporting data on ground-level UV radiation, ozone concentrations (or precursors) or public health indicators. The findings of the original review were confirmed; urban green areas tended to be cooler than urban non-green areas. Air temperature under trees was on average 0.8 °C cooler but treed areas could be warmer at night. Cooling effect showed tree species variation. Tree canopy shading was a significant effect modifier associated with attenuation of solar radiation during the day. Urban forests were on average 1.6 °C cooler than comparator areas. Treed areas and parks and gardens were associated with improved human thermal comfort. Park or garden cooling effect was on average 0.8 °C and trees were a significant influence on this during the day. Park or garden cooling effect extended up to 1.25 kms beyond their boundaries. Grassy areas were cooler than non-green comparators, both during daytime and at night, by on average 0.6 °C. Green roofs and walls showed surface temperature cooling effect (2 and 1.8 °C on average respectively) which was influenced by substrate water content, plant density and cover. Ground-level concentrations of nitrogen oxides were on average lower by 1.0 standard deviation units in green areas, with tree species variation in removal of these pollutants and emission of biogenic volatile organic compounds (precursors of ozone). No clear impact of green areas on ground level ozone concentrations was identified. Design of urban green areas may need to strike a balance between maximising tree canopy shading for day-time thermal comfort and enabling night-time cooling from open grassy areas. Choice of tree species needs to be guided by evapotranspiration potential, removal of nitrogen oxides and emission of biogenic volatile organic compounds. Choice of plant species and substrate composition for green roofs and walls needs to be tailored to local thermal comfort needs for optimal effect. Future research should, using robust study design, address identified evidence gaps and evaluate optimal design of urban green areas for specific circumstances, such as mitigating day or night-time urban heat island effect, availability of sustainable irrigation or optimal density and distribution of green areas. Future evidence synthesis should focus on optimal design of urban green areas for public health benefit.

中文翻译：

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城市地区的“绿化”在减少人类暴露于地面臭氧浓度、紫外线照射和“城市热岛效应”方面的效果如何？更新的系统评价

本综述更新了 2010 年发表的系统综述 ( http://www.environmentalevidence.org/completed-reviews/how-effective-is-greening-of-urban-areas-in-reducing-human-exposure-to-ground- level-ozone-concentrations-uv-exposure-and-the-urban-heat-island-effect ）解决了这个问题：城市地区的“绿化”在减少人类暴露于地面臭氧浓度、紫外线暴露和“城市热岛效应”？对多个数据库和期刊进行了相关已发表文章和灰色文献的搜索。在组织网站上搜索未发表的文章。资格标准适用于标题、摘要和全文，并对纳入的研究进行严格评价。对这些过程进行了一致性检查。从纳入的研究中提取预先定义的数据项。通过元分析进行定量综合，并进行叙述综合。本综述共纳入 308 项研究。研究遍及除极地以外的所有大陆和气候区，但主要集中在欧洲和温带地区。大多数研究报告了城市绿化对温度的影响，而较少的研究报告了地面紫外线辐射、臭氧浓度（或前体）或公共卫生指标的数据。原始审查的结果得到确认；城市绿地往往比城市非绿地凉爽。树下的气温平均低 0.8 °C，但树木繁茂的地区夜间可能会更暖和。降温效应表现为树种变异。树冠阴影是与白天太阳辐射衰减相关的显着效果调节剂。城市森林平均比比较地区低 1.6 °C。树木繁茂的地区、公园和花园与改善人体热舒适度有关。公园或花园的降温效果平均为 0.8 °C，白天树木对此有显着影响。公园或花园的降温效应可延伸至其边界外 1.25 公里。在白天和晚上，草地区域比非绿色区域的温度平均低 0.6 °C。绿色屋顶和墙壁显示出表面温度冷却效应（分别为 2 和 1.8 °C），其受基质含水量、植物密度和覆盖率的影响。绿色区域中氮氧化物的地面浓度平均降低了 1.0 个标准偏差单位，随着树种在去除这些污染物和排放生物挥发性有机化合物（臭氧的前体）方面的差异。没有发现绿色区域对地面臭氧浓度的明显影响。城市绿地的设计可能需要在最大化树冠遮阳以实现白天热舒适和夜间从开阔的草地区域冷却之间取得平衡。树种的选择需要以蒸发蒸腾潜力、氮氧化物的去除和生物挥发性有机化合物的排放为指导。绿色屋顶和墙壁的植物种类和基质成分的选择需要根据当地的热舒适需求进行定制，以获得最佳效果。未来的研究应该使用稳健的研究设计，解决已确定的证据差距并评估特定情况下城市绿地的最佳设计，例如减轻白天或夜间的城市热岛效应、可持续灌溉的可用性或绿地的最佳密度和分布。未来的证据合成应侧重于城市绿地的优化设计，以实现公共卫生效益。