One More Reason to Hug Trees
It is well known that vegetation is good at filtering air indoors (check out the list of the best air-filtering house plants according to NASA!) and outdoors, but a new research paper shows that they might be even better than we thought. And not just a little bit, but up to 8x more when it comes to common urban pollutants like nitrogen dioxide (NO2) and disease-causing particulate matter (PM).
The study concluded that judicious placement of grass, climbing ivy and other plants in urban canyons can reduce the concentration at street level of NO2 by as much as 40 percent and PM by 60 percent, much more than previously believed. The authors even suggest building plant-covered “green billboards” in these urban canyons to increase the amount of foliage. Trees were also shown to be effective, but only if care is taken to avoid trapping pollutants beneath their crowns.
It would be very interesting to do more studies and figure out how to get the maximum air-filtration effect out of urban vegetation, and then make sure that urban planners use those best practices. The world is urbanizing fast, and while we can improve the air quality in cities by making it easier to walk, cycle, or take transit and by electrifying vehicles, whatever air pollution is left should be cleaned up, and vegetation is our best ally to do that.