City trees, popularly thought to remove pollutants and improve urban life, may also increase the amount of foul air that people breathe, says the UK body which gives independent health guidance to national and local government.
“Leaves and branches slow air currents, causing pollutants to settle. They may also act as sinks for particulates and chemicals that may have direct or indirect effects in air quality. Air quality [under trees] may deteriorate at street level near vehicles,” says the National Institute for Health and Care Excellence (Nice) in new draft guidance for local government to combat air pollution.

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