Green plants reduce urban air pollution 8x more than expected

WASHINGTON, — The latest episode in the American Chemical Society’s (ACS’) award-winning Global Challenges/Chemistry Solutions podcast series concludes that trees, grass and other greenery growing in the concrete-and-glass canyons of cities can reduce levels of two of the most worrisome air pollutants by eight times more than previously believed.

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Based on a report by Thomas Pugh, Ph.D., in ACS’ journal Environmental Science & Technology, the podcast is available without charge at iTunes and from. In the new episode, Pugh and colleagues explain that concentrations of nitrogen dioxide and microscopic particulate matter — both of which can be harmful to human health — exceed safe levels on the streets of many cities. Past research suggested that trees and other green plants can improve urban air quality by removing those pollutants from the air. However, the reduction seemed to be small, typically less than 5 percent. The study sought a better understanding of the effects of green plants in the sometimes stagnant air of city streets bounded by buildings, which the authors term “urban street canyons.” It concluded that careful placement of grass, climbing ivy and other plants in urban canyons can reduce street-level concentrations of nitrogen dioxide by up to 40 percent and particulate matter by 60 percent. That is much more than previous studies indicated. Pugh also pointed out, however, that trees actually could worsen street-level air quality in the most polluted urban canyons. In these areas, trees might trap more pollutants than they could remove. The study suggested that urban planners consider the benefits of planting trees in these areas. Global Challenges/Chemistry Solutions is a series of podcasts describing some of the 21st century’s most daunting problems, and how cutting-edge research in chemistry matters in the quest for solutions. Global Challenges is the centerpiece in an alliance on sustainability between ACS and the Royal Society of Chemistry. Global Challenges is a sweeping panorama of global challenges that includes dilemmas such as providing a hungry, thirsty world with ample supplies of safe food and clean water; developing alternatives to petroleum to fuel society; preserving the environment and assuring a sustainable future for our children and improving human health. For more entertaining, informative science videos and podcasts from the ACS Office of Public Affairs, view Prized Science, Spellbound, Science Elements and Global Challenges/Chemistry Solutions.