Hedges planted at roadsides can cut black carbon by as much as 63%, in addition to other airborne pollutants.
In most crowded cities air pollution is pretty much a fact of life. You can protect yourself from it, at least to some extent, by spending much of your time indoors and wearing a protective face mask when you go outdoors.
Better yet, though: plant hedges around your house, if you can do so.
So say experts from the University of Surrey who examined the impact of roadside green infrastructure on higher concentrations of airborne pollutants. The researchers, who have published a study on it in the journal Atmospheric Environment, looked at six different combinations of roadside vegetation: only hedges, only trees and a mix of trees and hedges or shrubs, each planted either less than 1 meter apart or else more than 2 meters apart.
What they found was that roadsides with hedges were the most effective at reducing pollution exposure. Hedges cut black carbon by as much as 63% and also significantly reduced the amounts of airborne ultrafine and sub-micron particles. Hedges performed particularly well when winds ran parallel to a road, but also reduced air pollution when winds were blowing across the road.
Trees alone performed less well in reducing air pollution from exhaust fumes from cars, although a combination of hedges and trees also worked fairly well, especially when planted closer together.
Perhaps that result is not surprising since dense hedges can act as far better filters at street level where people actually breathe than trees with their foliage higher up above people’s heads. Urban planners should bear this in mind when planting vegetation, especially in areas with high levels of air pollution, the researchers note.
“The best way to tackle pollution is to control it at the source,” stresses Prof. Prashant Kumar, the study’s senior author and founding director of the university’s Global Centre for Clean Air Research. “However, reducing exposure to traffic emissions in near-road environments has a big part to play in improving health and well-being for city-dwellers,” he adds.
“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,” Kumar says. “Urban planners should consider planting denser hedges, and a combination of trees with hedges, in open-road environments.”