Trees Are Awesome: Study Shows Tree Leaves Can Capture 50%+ of Particulate Matter Pollution

CC BY-SA 2.0. Wikimedia

Nature's high-tech air scrubbers

Breathing is not optional, so air pollution matters. Recent studies by the World Health Organization (WHO) and five National Academies of Science and Medicine have shown that air pollution kills more people than AIDS and malaria combined and causes cancer—at least 5 million according to the academies. Thankfully, a lot of progress has been made in many places, but some others are still quite bad (especially in the Middle-East and Asia, and Europe could improve a lot too -- see the map below).

We always knew that trees are good air filters, but it's been hard to quantify just how much. One new study from Lancaster University, in the U.K., tried to do so. What they found is quite interesting, and one more reason to hug a tree today!

Air pollution map WHO

Map of global air pollution compiled by the World Health Organisation/Public Domain

The scientists started by measuring how much air pollution go into a certain number of houses in Lancaster using dust monitoring devices and by swiping surfaces and then analyzing what was collected with magnetic remanence, a technique that provides information on concentrations of iron-bearing particles.

Then the team placed a screen of 30 young silver birch trees in wooden planters in front of four of the houses, including one of the control houses, for 13 days. Wipes from all eight houses showed that ones with the tree screens had 52 to 65% lower concentrations of metallic particles. A comparison of all of the dust monitoring data from the two original control houses confirmed that drop, showing a 50% reduction in PM1, PM2.5, and PM10 in the house with the trees in front.
By examining the silver birch leaves with a scanning electron microscope, the researchers confirmed that the hairy surfaces of the leaves trapped metallic particles. Like the particles measured inside the houses, these metallic particles are most likely the product of combustion and brake wear from vehicles passing by. Previous work has indicated a strong correlation between the amount of material identified by magnetic remanence and benzo(a)pyrene, a carcinogenic polycyclic aromatic hydrocarbon found in particulates, Maher says. (source)
Trees in Chicago photo

© Michael Graham Richard

So when do we start planting trees everywhere? Not that we needed this study to tell us that it's a good idea, but it never hurts to add some evidence on top of the mountain that we already have.

If you're looking to do this on a smaller scale, try adding air-filtering indoor plants approved by NASA.