How planting hedges can reduce near-road pollution exposure

How planting hedges can reduce near-road pollution exposure
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Planting hedges, or a combination of trees with hedges, is an effective way to reduce near-road pollution exposure, according to a new study from the University of Surrey.

The study suggests that urban planners should focus on planting hedges to minimise the levels of near-road pollution exposure in urban environments.

Combatting near-road pollution exposure

According to the United Nations, over half of the global population live in urban areas. In the European Union specifically, two thirds of the population live in urban areas. The European Environmental Agency say that air pollution levels in many cities in the European Union are above permissible levels.

Professor Prashant Kumar, the senior author of the study and the founding Director of the GCARE at the University of Surrey, said: “Many millions of people across the world live in urban areas where the pollution levels are also the highest. The best way to tackle pollution is to control it at the source. 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. The iSCAPE project provided us with an opportunity to assess the effectiveness of passive control measures such as green infrastructure that is placed between the source and receptors.”

Why should urban planners focus on planting hedges?

The study assessed three types of roadside green infrastructure (trees, hedges, and a combination of trees with hedges and shrubs) affected the concentration levels of pollution.

Six locations in Guildford, UK, were used as test sites to assess the near-road pollution. The green infrastructure was between one to two metres away from the road.

The researchers found that:

  • The roadsides which had only hedges were the most effective at reducing pollution exposure, cutting black carbon by up to 63 percent; and
  • Roadsides with only trees showed no positive influence on pollution reduction at breathing height. This is because the tree canopy was too high to provide a barrier/filtering effect for road-level tailpipe emissions.

The hedges only, or a combination of hedges and trees, were the most effective green infrastructure in improving air quality behind them under different wind directions.

Kumar added: “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… 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.”

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