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Environment & Climate Change

How much do urban trees help with particle pollution?

Photo courtesy of Fellowship of the Rich, Flickr
Grand Rapids is trying to take better care of its city trees.

It’s no secret that trees do some good things for us. But scientists are putting numbers on just how good trees are at removing certain kinds of pollution from the air.

David Nowak is a project leader with the U.S. Forest Service.  He and his team looked at the overall impact urban trees have on fine particle pollution (their study is published in the journal Environmental Pollution). Those are very tiny particles found in smoke and haze.

“These particles tend to stay in the atmosphere longer and tend to go deeper into your lung system and have greater human health impacts,” says Nowak.

Here's what the Environmental Protection Agency says about particle pollution:

Particle pollution - especially fine particles - contains microscopic solids or liquid droplets that are so small that they can get deep into the lungs and cause serious health problems. Numerous scientific studies have linked particle pollution exposure to a variety of problems, including: premature death in people with heart or lung disease, nonfatal heart attacks, irregular heartbeat, aggravated asthma, decreased lung function, and increased respiratory symptoms, such as irritation of the airways, coughing or difficulty breathing. People with heart or lung diseases, children and older adults are the most likely to be affected by particle pollution exposure. However, even if you are healthy, you may experience temporary symptoms from exposure to elevated levels of particle pollution.

Nowak and his team looked at ten cities across the U.S. (Atlanta, Chicago, Los Angeles and Minneapolis among them).  He found that urban trees removed a small amount of fine particle pollution. That pollution can stick to a tree’s leaves.

“We’re talking fractions of a percent annually. But because of these health impacts, even minor changes from the plants have health impacts on humans,” says Nowak.

Nowak says trees do help reduce air pollution, but it’s much better to reduce particle pollution at the source, from things like power plants, cars and industries.