City trees and air pollution

The controversial comments regarding speed bumps and urban trees arise out of the guidance published in 2017 by the National Institute for Health and Care Excellence (NICE). The NICE committee “felt it was appropriate to recommend caution when using street trees and not to consider them as always being beneficial, because if they are poorly placed or maintained this may affect ventilation at street level and inadvertently create a canopy that traps air pollutants”.

However, the guidance recognises that well-placed trees bring benefits for air quality and recommends that rather than being removed, trees should be managed (by siting, pruning, etc) so that they do not restrict street ventilation.