With more than half the world’s population (75 percent in the United States) living in cities or towns, and more people driving than ever before, there’s a growing incentive to improve urban air now while it’s still (gasp) somewhat breathable.
Plants breathe in CO2 and release oxygen—an ideal combination for our highly carbon emitting ways. They also suck up other pollutants like nitrogen dioxide (NO2) and particulates such as dust and smoke, making them a perfect complement for cities choking in smog. It’s this effectiveness at combating pollution that has caused city government’s worldwide to aggressively grow their tree canopies.
Scientists at the University of Birmingham are looking up, not at trees, but at skyscrapers for the next pollution solution. They want to use this vertical real estate by planting climbing plants on billboard-like structures and placing them on walls, which is expected to reduce pollution by up to 30 percent—a far better outcome than planting trees in urban areas, which can only cut about 5 percent of pollution.
Much research has been done on the benefits of trees, which also applies to plants. Aside from reducing pollution, they lower ambient temperature (which can rise dramatically from the green outskirts of a city to the downtown core due to the heat island effect, even as much as 22 degrees F (12 degrees C) difference in the evening, according to the EPA). An acre of trees stores as much carbon as a car driven 26,000 miles. They reduce soil erosion and prevent floods. And they also humidify the air by releasing water vapour.
Trees benefit people too. Research has found that they can improve well-being and reduce the stress of those living around a lot of them. They increase property value as well, which might be another contributor to people’s well-being and reduced stress.
But according to the study, trees are only effective at cleaning air in areas with minimal pollution. The dirty downtown core of most major urban centres demands a more aggressive approach.
Tall buildings and traffic are a bad combination. Vehicles pollute the air and the buildings form street canyons that block pollution from escaping. Luckily, all these street canyons also mean a lot of places to plant.
Green walls are nothing elaborate. Just planting simple creepers like ivy work best. Though as with tree planting, it isn’t good enough to just plant vegetation on the walls and hope for the best, they have to be planted properly and in the right location to avoid drought, heat stress and vandalism.
Urban planners know the value of trees as a public works asset. Cities have so much vertical real estate just waiting to be put to use. From an environmental, economic and health perspective it makes sense to use these walls to build up a city’s green infrastructure.
The term “concrete jungle” has long been used to point out a city’s greatest weakness, it’s disconnection from nature. Enveloping citizens in green walls can fundamentally transform a city’s landscape from a dull, lifeless land of concrete to an alive, breathing garden of life while also cutting down on pollution—a wise utilization of an already existing resource.
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