According to scientists at the British universities of Birmingham and Lancaster, greening streets with trees, bushes and living walls, could cut pollution by as much as 30 percent. This is more than 10 times what was previously thought.
Research published in the Environmental Science and Technology journal reports that growing vegetation in the concrete-and-glass urban canyons of cities would deliver cleaner air at street level where most people are exposed to the highest pollution, and could be implemented street-by-street without the need for large-scale and expensive initiatives, according to 2 degrees.
Plants in cities clean the air by removing nitrogen dioxide and microscopic particulate matter, both of which are harmful to human health. These pollutants are significant problems in cities in developed and developing countries: the UK Government Environmental Audit Committee estimates are that outdoor air pollution causes 35,000-50,000 premature deaths per year in the UK, while the World Health Organization's outdoor air quality database puts the figure at more than 1 million worldwide.
The researchers have found that, because pollution cannot easily escape these concrete-and-glass urban canyons, green walls of grass, climbing ivy and other plants have a better opportunity than previously thought to act as an air pollution filter. Instead of reducing pollution by 1 percent or 2 percent, reductions of more than 10 times this magnitude could be achieved.
Using a computer model that captures the trapping of air in street canyons, as well as the hundreds of chemical reactions that can affect pollution concentrations, the research team could distinguish the effects of plants in canyons from those of plants in parks or on roofs. Green walls emerged as clear winners in terms of pollutant removal. Street trees were also effective, but only in less polluted streets where the tree crowns did not cause pollution to be trapped at ground level.
Professor Rob MacKenzie, from the University of Birmingham's School of Geography, Earth and Environmental Sciences, said, "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. 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."
Read more about green landscaping.