In the never-ending search for cleaner air in our cities, ‘canyons’ have long been a sticking point. Those canyons are the ones enclosed on both sides by tall buildings and holding the traffic arteries that carry hoards of pollution-emitting vehicles to and fro in any large city. Up until recently the common assumption was that greenery in the form of trees, grass, vines and shrubs could only reduce that pollution by about 5%.
New studies from several agencies indicate that strategically placed greenery can do much better than that. Findings published in the Journal of Environmental Science and Technology have demonstrated that nitrogen dioxide (NO2) and particulate matter (PM) can be reduced by at least 30% with the incorporation of innovative ‘green walls’ into the urban landscape.
One such study conducted by Prof. Thomas Pugh of Lancaster University and Robert MacKenzie at the University of Birmingham focused on the effects of added greenery in urban canyons. Their findings, published in Science Daily, concluded that proper placement of grass, ivy and other climbing vines and plants can reduce NO2 at street level by up to 40% and particulate matter by as much as 60%.
Green walls, those literally covered in living foliage, are possibly the most efficient air cleaners; trees work well too, but you have to be careful that polluted air doesn’t get trapped beneath their canopies. The biggest problems with all this greenery are the cost of planting it and the ongoing cost of keeping it healthy.
Transport for London (TfL) has been working on the concept for a couple of years now, and the head of environment (surface transport) Nicola Cheetham says their own research supports the other findings.
London now has two green walls, at Edgeware Road tube station and The Mermaid in Blackfriar, with plans for more. Besides cleaning up the air in the streets, they offer the added bonus of considerable aesthetic attraction.