Evergreens with smaller leaves found to be more effective at reducing roadside pollution, according to ground-breaking research at the University of Surrey

Small evergreen leaves are better at catching roadside pollution than big deciduous leaves, groundbreaking Surrey research reveals
Professor Prashant Kumar is founder of the University of Surrey's Global Centre for Clean Air Research. Picture: Dean WhitingProfessor Prashant Kumar is founder of the University of Surrey's Global Centre for Clean Air Research. Picture: Dean Whiting
Professor Prashant Kumar is founder of the University of Surrey's Global Centre for Clean Air Research. Picture: Dean Whiting

Experiments at the University of Surrey into 10 species of UK trees looked at which ones caught the largest number of pollution particles when placed beside the busy A3 road in Guildford.

Researchers measured the number of particles caught by the different leaves – and how effectively they were washed away by the rain, keeping the surrounding air clean.

Hide Ad
Hide Ad

Professor Prashant Kumar, founder of the University of Surrey's Global Centre for Clean Air Research, said: These particles are harmful when they are suspended in the air because people breathe them in but when they are collected on surfaces they are washed off by the rain and just end up in bodies of water.”

The particles may still be there but their impact on the environment is not as severe as when people breathe them in.

Prof. Kumar, explained: “This study builds upon substantial work we have been doing around urban greening and where you should be putting the plants and what type of plants, to get the benefits of air pollution reduction along the roadside.”

The importance of finding the best tree for the job has come at a crucial time as the UK government is attempting to increase “green cover” to 40% in residential areas across the UK. The Government’s report found that 80% of people are now living in towns and cities.

Hide Ad
Hide Ad

It also found one third of people do not have access to good quality green and blue space within 15 minutes of their home.

Professor Kumar said: "This work extends the legacy of understanding the features of different hedge or tree species and how many particles they capture and which is most efficient."

Of the trees studied, the Yew tree was found to be most effective at removing air pollution and the most effective leaf types were awl-shaped. They were found on Japanese Cedar and Lawson's Cypress.

According to Prof. Kumar, “It is quite unique looking at these specific species which are very local to the UK and their characteristics.”

Hide Ad
Hide Ad

The study assessed data collected across three rainfalls at different times of the year, starting in April, then June and another one in February. The evergreens are more effective as they have a larger net effect across the year due to the trees keeping their leaves all year round.

Despite the obvious advantage that evergreens maintain over deciduous trees, Kumar points out that “there is always a factor of diversity you need to maintain and so we need a mix of the species that we plant on our roadsides.”

The team is now repeating the test in the same location, this time using three species of hedges.