If you’re trying to take pollution out of the air, choose evergreen trees with smaller leaves. That’s according to a new study from the University of Surrey.

Researchers from Surrey’s Global Centre for Clean Air Research (GCARE) tested ten trees beside a busy main road. They studied which caught the most particles of pollution and which best allowed the rain to wash those particles safely to the ground.

It had been thought that leaves with rougher surfaces and minute hairs would catch more pollutants. Yet that wasn’t borne out by the evidence.

Yendle Barwise, University of Surrey researcher.

Many planting projects use deciduous trees, which lose their leaves in winter – even though that’s when air pollution is worst in towns and cities.

For that reason, scientists chose ten evergreen specimens and placed them in plant pots beside the A3 in Guildford. Some 80,000 vehicles drive past every day.

Of those studied, Yew (taxus baccata) was the plant which removed most air pollution. The most effective leaf types were awl-shaped. They were found on Japanese Cedar (camellia japonica) and Lawson’s Cypress (chamaecyparis lawsoniana).

The study also suggested that stomata – the ‘pores’ of the leaf – could help plants’ catch’ particles. For Yew, more particles of pollution gathered on the porous underside of the leaf. That’s despite the other side of the leaf being 47% rougher, and despite previous research suggesting roughness mattered more.

The paper is published in the journal Science of the Total Environment.

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