How effective is ‘greening’ of urban areas in reducing human exposure to ground-level ozone concentrations, UV exposure and the ‘urban heat island effect’? An updated systematic review

Environmental Evidence

Raja Lorena Richter¹  Diana Bowler²  Sian King³  Teri Knight⁴  Amy Hookway⁵  Sian Price⁶  Ko Konno⁷ 

[1] Faculty of Veterinary Medicine, University of Leipzig, An den Tierkliniken 1-43, 04103, Leipzig, Germany;German Centre for Integrative Biodiversity Research (iDiv), Friedrich Schiller University Jena, Halle-Jena-Leipzig, Deutscher Pl. 5E, 04103, Leipzig, Germany;Public Health Wales, 1st Floor, Matrix House, Northern Boulevard, Matrix Park, Swansea Enterprise Park, SA6 8DP, Swansea, UK;Public Health Wales, 2 Capital Quarter, Tyndall Street, CF10 4BZ, Cardiff, UK;Public Health Wales, Floor 5, Number 2 Capital Quarter, Tyndall Street, CF10 4BZ, Cardiff, UK;Public Health Wales, PO Box 108, Building 1, St David’s Park, SA31 3WY, Carmarthen, UK;School of Natural Sciences, Bangor University, LL57 2UW, Bangor, UK;

关键词: Urban;    Greening;    Ground-level ozone;    UV radiation;    Heat-island;    Updated systematic review;   

DOI  :  10.1186/s13750-021-00226-y

来源: Springer

【 摘 要 】

BackgroundThis 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’?MethodsSearches 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 Organisational websites were searched for unpublished articles.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.Review findings308 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.ConclusionsDesign 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.

【 授权许可】

CC BY