The University of Surrey – specifically Professor Prashant Kumar – have just completed a study to find out whether roadside planting (hedges and/or trees) can reduce road air pollution. (You can read about it in detail in Atmospheric Environment here.) And, as my good friends Tom Ogren and Nigel Clarke could have told us, it turns out that hedges in particular are extremely good at reducing pollution.
Indeed, according to Professor Kumar’s research hedges along a road side would cut the black carbon that is breathed in as you walked along the pavement by 63%. Trees, on the other hand, delightful though they may be, achieve very little as the leaf canopy is too high to affect the air quality at human breathing level.
Given that, according to the UN, more than half of the world’s population live in urban areas (two thirds of the population in the EU) – and that air pollution is all too often way above permissible levels making air pollution a ‘primary environmental health risk’ – planting hedges seems like a bit a no brainer. As Prof. Kumar points out:
“This study, which extends our previous work, provides new evidence to show the important role strategically placed roadside hedges can play in reducing pollution exposure for pedestrians, cyclists and people who live close to roads. Urban planners should consider planting denser hedges, and a combination of trees with hedges, in open-road environments.
Many local authorities have, with the best of intentions, put a great emphasis on urban greening in recent years. However, the dominant focus has been on roadside trees, while there are many miles of fences in urban areas that could be readily complemented with hedges, with appreciable air pollution exposure dividend.
Urban vegetation is important given the broad role it can play in urban ecosystems – and this could be about much more than just trees on wide urban roads.”