In last month’s Clean Air Notes, we talked about the air quality benefit of trees.  In this month’s Clean Air Notes, we discuss which trees work best to remove air pollution.  Some trees are better able to remove air pollution than others.  Of those that can remove air pollution, some are better at absorbing ozone pollution while others are better at capturing particulate matter.  Both offer a benefit to air quality! 

Ozone and other gaseous pollutants are removed by trees through their leaf stomata where trees and plants perform their normal gas exchange that includes taking in carbon dioxide and releasing oxygen.¹ After being absorbed into the leaf, the pollutants are converted to less harmful substances or broken down. ² Some of the best trees to plant for ozone reduction include the common beech, London plane, maple, tulip, and horse chestnut trees. ³

Particulate matter is not absorbed by trees but can be captured on leaves, especially those that are waxy, resinous, hairy, or scaly.  It can also be captured by uneven, rough branch surfaces.¹ The leaves and branches capture the particulate matter until rain fall removes the pollutants from the tree surfaces and deposits them on the ground. ² Some of the recommended trees for filtering particulate matter are the English oak with rough leaves, the silver birch with leaves that are covered in tiny hairs, and the ginkgo biloba that has a large surface area for particulate matter capture. ² Evergreen trees like the eastern white pine and cypress trees are also good for filtering particulate matter and offer the benefit of keeping their dense needles throughout the year allowing for air quality benefits year-round!²

¹   Center for Urban Forest Research, Trees – The Air Pollution Solution, https://www.fs.usda.gov/psw/topics/urban_forestry/products/cufr_658_Air _pollution_solution.pdf.

²   Biology Insights, Which Trees are Best for Cleaning the Air, https://biologyinsights.com/which-trees-are -best-for-cleaning-the-air/

³   Science, Ozone-reducing urban plants: Choose carefully, https://www.science.org/doi/10.1126/science.add9734