Urban air pollution could be more effectively tackled in built up areas by strategically planting hedges along roads, rather than larger trees, researchers say.

The UK, US and EU research found that in areas populated with large buildings on both sides of the road, trees tended to make pollution more concentrated, while hedges reduced exposure.

However in “open road” conditions, thick, tall and dense vegetation was best at restricting freshly emitted vehicle emissions from reaching the roadside in high concentrations. Green walls and roofs also acted as a “sink” to reduce pollution, the research found.

It is these kinds of findings that lead author Professor Prashant Kumar, who is from the University of Surrey, hopes will lead to better urban planning outcomes.

“We all know air pollution is a major factor of everyday urban life,” he said.

“This comprehensive review highlights that trees and hedges, as well as other green infrastructure, must be used strategically to help create healthier, less polluted cities that are also more pleasant for everyone to live and work in.”

A previous study by Professor Kumar also showed that buildings too needed protection from air pollution.

“Our earlier study showed the weathering impact of air pollution on the building materials such as limestone, sandstone and carbon steel, used in many heritage buildings and built infrastructure,” Professor Kumar said.

“This is why we need to protect buildings as well as humans in cities in future urban planning, so the strategic placing of hedges, trees and other green infrastructure can have a direct benefit as an air pollution control measure in cities.”

He said additional benefits of green infrastructure included urban heat island mitigation, the potential reduction in energy consumption, better stormwater management and climate change mitigation.

The research forms part of the iSCAPE: Improving Smart Control of Air Pollution in Europe project, the next step of which will be to quantify the effects of different types of greenery along busy open roadsides.

“This will help to develop evidence-based guidelines to support future urban planning and the public to make informed choices to ‘green up’ their surrounding environments,” Professor Kumar said.

The research has been published in Atmospheric Environment.

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