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Environ Pollut. 2018 Dec;243(Pt A):163-176. doi: 10.1016/j.envpol.2018.08.049. Epub 2018 Aug 20.

Should we see urban trees as effective solutions to reduce increasing ozone levels in cities?

Author information

ARGANS, Sophia Antipolis, France. Electronic address:
Hokkaido Research Centre, Forestry and Forest Products Research Institute, Sapporo, Japan; Research Faculty of Agriculture, Hokkaido University, Sapporo, Japan.
Lithuanian Research Centre for Agriculture and Forestry, Institute of Forestry, Girionys, Lithuania.
Consiglio Nazionale Delle Ricerche, Sesto Fiorentino, Italy.
Italian National Agency for New Technologies, Energy and Sustainable Economic Development, Rome, Italy.


Outdoor air pollution is considered as the most serious environmental problem for human health, associated with some million deaths worldwide per year. Cities have to cope with the challenges due to poor air quality impacting human health and citizen well-being. According to an analysis in the framework of this study, the annual mean concentrations of tropospheric ozone (O3) have been increasing by on average 0.16 ppb year-1 in cities across the globe over the time period 1995-2014. Green urban infrastructure can improve air quality by removing O3. To efficiently reduce O3 in cities, it is important to define suitable urban forest management, including proper species selection, with focus on the removal ability of O3 and other air pollutants, biogenic emission rates, allergenic effects and maintenance requirements. This study reanalyzes the literature to i) quantify O3 removal by urban vegetation categorized into trees/shrubs and green roofs; ii) rank 95 urban plant species based on the ability to maximize air quality and minimize disservices, and iii) provide novel insights on the management of urban green spaces to maximize urban air quality. Trees showed higher O3 removal capacity (3.4 g m-2 year-1 on average) than green roofs (2.9 g m-2 year-1 as average removal rate), with lower installation and maintenance costs (around 10 times). To overcome present gaps and uncertainties, a novel Species-specific Air Quality Index (S-AQI) of suitability to air quality improvement is proposed for tree/shrub species. We recommend city planners to select species with an S-AQI>8, i.e. with high O3 removal capacity, O3-tolerant, resistant to pests and diseases, tolerant to drought and non-allergenic (e.g. Acer sp., Carpinus sp., Larix decidua, Prunus sp.). Green roofs can be used to supplement urban trees in improving air quality in cities. Urban vegetation, as a cost-effective and nature-based approach, aids in meeting clean air standards and should be taken into account by policy-makers.


Air pollution; Green infrastructure; Green roof; Mitigation; Urban forest

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