Scientific study – Green walls lead to cleaner cities

from the journal Environmental Science and Technology

We’ve been involved with greenwalls since 2008, and a frequent question we get is “why green walls?”  Typically green roof projects can justify their existence (environmentally, at least), by retaining storm water and reducing the urban heat island effect, along with other benefits.  Greenwalls don’t have that luxury – while they do insulate a wall of a building, it’s hard to cover enough of the wall to provide significant benefit. Typically we find they are installed for the visual effect more than any other reason.

Finally, there has been a study that provides compelling environmental benefits to putting greenwalls throughout cities.


Planting living “green walls” of vegetation could provide a faster and cheaper way of cleaning up the air in cities than large-scale initiatives such as congestion charging, scientists will say today.

Reductions of street level pollution of as much as 30 per cent could be achieved at a low cost simply by growing trees, bushes, and other greenery amid the concrete and glass “street canyons” that characterize modern cities, according to new research published in the journal Environmental Science and Technology.

Plants clean the air of nitrogen dioxide and particulate matter, which are blamed for a significant portion of the 35,000 to 50,000 of premature UK deaths that are attributed to outdoor air pollution each year. The World Health Organisation’s outdoor air quality database puts the figure of air quality related premature deaths at more than one million a year worldwide.

Scientists at the Universities of Birmingham and Lancaster say pollution struggles to escape “street canyons”, which makes planting green walls of grass, climbing ivy and other plants far more effective at filtering out pollutants than previously thought.

Computer modelling suggested green walls trumped plants in parks and on roofs, as well as street trees, which were most effective in less polluted streets where high level leaves did not trap polluted air at ground level.

The scientists say rolling out more foliage would be simple to achieve on a street-by-street basis, while plant covered “green billboards” could be installed in urban canyons. Although they also warned care would have to be taken to grow hardy vegetation that can cope with drought, heat stress, or vandalism.

“Up until now, every initiative around reducing pollution has taken a top-down approach – scrapping old cars, adding catalytic converters to cars, and bringing in the congestion charge – some of which have not had the desired effect,” said Professor Rob MacKenzie, professor of atmospheric science at the University of Birmingham.

“The benefit of green walls is that they clean up the air coming into and staying in the street canyon – planting more of these in a strategic way, could be a relatively easy way to take control of our local pollution problems.”

This is the first real solid research we’ve seen in this direction. Obviously we’re enthusiastic about the premise – it remains to be seen if this can be proven in a real context. The City of London has been attempting to test this in several locations – we’ll see what their results are.

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