Plantwatch: how urban trees and hedges help cut air pollution

Paul Simons

Hedges and trees in towns and cities are more than just attractive, they can behave like natural air filters, trapping traffic pollution made up of dangerous microscopic particles blamed for a range of serious health problems, ranging from heart disease, asthma and strokes to diabetes, obesity and dementia.

A study at Lancaster University showed that silver birch trees maintained as hedges at about the height of an adult person were particularly good at cleaning the air.

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Their leaves are covered in tiny hairs and ridges that help trap the polluting particles and each time it rains the particles are washed off the leaves, freeing them to trap more particles. The suggestion is that the trees could be planted at pollution hotspots.

A study at the University of Surrey also found hedges or a combination of hedges and trees help to cut down the spread of air pollution from roads, including black carbon, harmful heavy metals and microscopic particles. The hedges acted as barriers at breathing height, usually between 1.5 and 1.7 metres.

And quite apart from scrubbing the air clean, hedges and their trees also help to cool the atmosphere in cities, protect against flooding by soaking up heavy rainfalls, and absorb carbon dioxide.