Plant hedges to combat near-road pollution exposure

January 4, 2019, University of Surrey
Credit: CC0 Public Domain

Urban planners should plant hedges, or a combination of trees with hedges—rather than just relying on roadside trees—if they are to most effectively reduce pollution exposure from cars in near-road environments, finds a new study from the University of Surrey.

In a paper published in Atmospheric Environment, researchers from the Global Centre for Clean Air Research (GCARE) looked at how three types of road-side green infrastructure—, hedges, and a combination of trees with hedges and shrubs—affected the concentration levels of air . The study used six roadside locations in Guildford, UK, as test sites where the green infrastructure was between one to two metres away from the road.

The researchers found that roadsides that only had hedges were the most effective at reducing , cutting black carbon by up to 63 percent. Ultrafine and sub-micron particles followed this reduction trend, with (less than 2.5 micrometres in diameter) showing the least reduction among all the measured pollutants. The maximum reduction in concentrations was observed when the winds were parallel to the road due to a sweeping effect, followed by winds across the road. The elemental composition of particles indicated an appreciable reduction in harmful heavy metals originating from traffic behind the vegetation.

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

Roadsides with only trees showed no positive influence on pollution reduction at breathing height (usually between 1.5 and 1.7m), as the tree canopy was too high to provide a barrier/filtering effect for road-level tailpipe emissions.

According to the United Nations, more than half of the global population live in —this number increases to almost two thirds in the European Union where, according to the European Environmental Agency, air pollution levels in many cities are above permissible levels, making air pollution a primary environmental health risk.

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."

"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 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", adds Professor Kumar.

Explore further: Cities need to 'green up' to reduce the impact of air pollution

More information: K.V. Abhijith et al, Field investigations for evaluating green infrastructure effects on air quality in open-road conditions, Atmospheric Environment (2019). DOI: 10.1016/j.atmosenv.2018.12.036

Related Stories

Recommended for you

Fish-inspired material changes color using nanocolumns

March 20, 2019

Inspired by the flashing colors of the neon tetra fish, researchers have developed a technique for changing the color of a material by manipulating the orientation of nanostructured columns in the material.

Researchers shed new light on the origins of modern humans

March 20, 2019

Researchers from the University of Huddersfield, with colleagues from the University of Cambridge and the University of Minho in Braga, have been using a genetic approach to tackle one of the most intractable questions of ...

One transistor for all purposes

March 20, 2019

In mobiles, fridges, planes – transistors are everywhere. But they often operate only within a restricted current range. LMU physicists have now developed an organic transistor that functions perfectly under both low and ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

billpress11
not rated yet Jan 05, 2019
Hedges could also be used as a barrier between opposing lanes on Interstate highways. In addition they could cut down on light glare at nighttime between the lanes. They can also make excellent noise barriers.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.