A recent study suggests that plants are even more effective at reducing air pollution in urban centers than previously thought.
According to Thomas Pugh and his colleagues, plants filter far more of two pollutants toxic to humans, nitrogen dioxide (NO2) and microscopic particulate matter (MP), from the air of dense urban centers than previous studies seemed to have shown.
Initial estimates suggested only a reduction of 5% or less for both pollutants in so-called “urban canyons” (places where the street is densely lined with buildings on both sides, creating a canyonlike environment where air exchange can be minimal), but this study indicates rather a reduction of N02 up to 40% and of PM by up to 60%, a truly significant contribution.
Vines are the most efficient at depolluting the air in urban canyons, as they can be allowed to climb up the sides of buildings whether they take up little to no valuable horizontal space, yet provide abundant foliage that filters the air. There is room for vines on even the narrowest urban streets. And no, vines don’t damage buildings, despite a persistent belief that claims the contrary). Shrubs, perennials, and grasses are also very effective. Trees can also be effective, but only if care is taken to avoid trapping pollutants beneath their canopy.
The authors even suggest the installation of “green billboards” (independent green walls, covered with vegetation on both sides) in the most polluted urban canyons to increase the amount of air-filtering foliage.