Roadside Hedges Could Reduce Air Pollution by 63%

Air pollution is a big problem for big cities, but a new study finds that humble roadside hedges may be able to help.

Teams from the Global Centre for Clean Air Research (GCARE) did the research, published this month in the journal “Atmospheric Environment”. They looked at how roadside environments change exposure to road traffic pollution. Urban planners have tended to favor lining roadsides with trees under the belief that trees can clean our air of harmful carbon emissions.

However, this has come at a cost: many of our roadside hedges have disappeared over the years and have not been renewed as a result. The researchers in this study sought to compare how trees, hedges and a combination of trees and hedges might change roadside air pollution exposure to get a better idea of the “ideal” roadside air-clearing greenery.

To do this, they used six roadside sites in Southern England. These areas contained a good mix of the tested greenery, and the greenery at each site was between one to two meters from the road, allowing the scientists to cut down on variables that might affect the results.

What the researchers found was that, perhaps surprisingly, roadsides that had only hedges were actually more effective at cutting pollution—in some cases by as much as 63 percent when it came to the cancer-causing pollutant black carbon.

This did change depending on the winds that day, with the hedges proving most effective when the winds were blowing parallel to the road, but overall the hedges performed best out of the three tested criteria. Hedges and tree mixes were the next best option. The pattern of reduction occurred across all expected measured pollutants, however ultrafine particles that can be found in traffic pollution showed the least reduction. This is not unexpected, as ultrafine pollutants are notoriously difficult to deal with (and to even monitor).

What is perhaps most interesting is that this study found no evidence supporting the conventional wisdom around using trees as air pollution fighters. In fact, the study found that tree-only roadsides showed no positive impact on pollution at the height where people would be breathing that polluted air. This is likely down to the fact that trees are too tall to catch to emissions that are made so close to the ground. Hedges, however, which are relatively short, do have that advantage.

“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,” Professor Prashant Kumar of GCARE said in a press release. “Urban planners should consider planting denser hedges, and a combination of trees with hedges, in open-road environments.”

Professor Kumar goes on to praise local authorities for putting an emphasis on urban greening over the past few years but said those schemes have relied on planting trees. But, he said, we could easily replace or supplement fences with hedgerows, allowing local authorities to maximize this urban greening and cut pollution with relatively little need for changing roadside infrastructure.

There are several other reasons why a return to hedgerows could be a significant win for our urban and semi-urban environments.

Across the UK and much of Europe, we have seen a steep decline in insects; small birds, like the sparrow; small mammals, like the hedgehog. At the same time, we have seen a decline in our hedgerows as the farming sector has done away with them to make space for intensive crop farming. Urban environments have also reduced hedgerows, again in favor of trees.

Many of the declining species once used hedgerows for shelter, nesting grounds and in a more general sense as part of their everyday lives. The link between a decline in hedgerows and some of Britain’s most iconic species is noted even at the highest levels of government, and though it is definitely not the sole factor, it is one that is relatively easy to change.

As this admittedly small but interesting study shows, a return to using hedgerows would be good for humans and for many flagging urban and suburban animal species.

Photo credit: Getty Images.

55 comments

Barbara S
Barbara S8 days ago

thanks for sharing

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Tabot T
Tabot T8 days ago

Thank you for sharing!

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Leanne K
Leanne K8 days ago

Roadside planting is usually to catch and hide all that litter. But when its time to clean up, which is damn rare, they just bull doze the lot. Think of that next time you hurl something out the window. Oh sure you dont

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Leanne K
Leanne K8 days ago

Dont you dare cut down the trees. Plant hedgings or thick growing bushes that are indigenous to the area by all means.

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Pam Bruce
Pam Bruce8 days ago

Not only hedges along the road ways would be helpful but putting shelterbelts in the middle of farmed fields like there used to be. These hedges and shelterbelts provide habitat for wildlife along with preventing erosion. Go back to the old methods of farming.

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Rebecca S
Rebecca S8 days ago

In the USA we have been cutting down hedges for decades it's no longer fashionable. The UK has miles of lovely hedges ones with berries provide food for wildlife as well. It would wonderful to have hedges everywhere!

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Clare O'Beara
Clare O'Beara9 days ago

Windbreaks for animals.

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Clare O'Beara
Clare O'Beara9 days ago

Hedges also provide a way for water to follow roots down into the ground and provide a snow block.

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Clare O'Beara
Clare O'Beara9 days ago

This has long been known.

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Danuta W
Danuta W9 days ago

Thanks for posting.

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