Effect of tree canopy cover on air pollution-related mortality in European cities: an integrated approach

In urban areas, fine particles (PM_2·5), nitrogen dioxide (NO₂), and tropospheric ozone (O₃) are the most harmful air pollutants for human health. Urban greening is seen as a strategy for co-benefitting air quality, climate, and citizens' wellbeing. We aimed to estimate the changes in tree cover, the mortality burden attributable to air pollution, and the mortality that could be potentially prevented by increasing tree coverage in European cities.

We did a quantitative health impact assessment to estimate the effect of mean tree cover on air pollutants levels and PM_2·5-related, NO₂-related, and O₃-related mortality (all ages) in 744 European urban centres, with more than 50 000 inhabitants, across 36 countries. We did all analyses at the city-wide scale.

Between 2000 and 2019, the mean tree coverage increased by 0·76 percentage points, with 73·5% of the urban centres showing greener coverage, whereas mortality burdens declined by on average 3·39% (SD 0·28) in all urban centres. In 2019, about 25% of the total population lived in areas with a mean tree canopy coverage over 30%. Compared with the current tree cover, each five percentage point increase in tree canopy cover could facilitate an air quality improvement of 2·8% for annual PM_2·5 mean concentrations, 1·4% for annual NO₂ mean concentrations, and 1·2% for summertime mean of the daily maximum 8-h O₃ concentrations.

We estimated that each five percentage point increase in tree canopy would potentially prevent 4727 premature deaths (95% CI 2067-7475) related to air pollution annually across the 744 European urban centres. We also estimated that reaching a canopy cover of 30% within each city could potentially prevent 11974 premature deaths (95% CI 7775-14 390) each year. Our results highlighted the potential public health benefits of increasing tree coverage in urban environments, contributing to sustainable, liveable, and healthier cities.

LIFE financial instrument of the EU; Romanian National Research Authority; Agencia Estatal de Investigación, Ministerio de Ciencia e Innovación; Generalitat Valenciana; The European Regional Development Fund; and National Natural Science Foundation of China.