Portland’s tree canopy removes enough nitrogen dioxide from the air to save society $6.6 million a year, based on avoided health care costs and the value of missed school and work days, according to a study by Portland State University researchers.

PSU’s Trees and Health team worked with volunteers, including PSU and Washington State University students, to place a web of 144 sensors across the Portland region. They compared neighborhood-level air quality data and correlated that with maps of Portland’s tree canopy, to create a new way to project and compare what it’s like to breathe in different parts of the city.

The nitrogen dioxide impact from trees was significant, because it pollutes the air and contributes to respiratory illnesses including asthma.

The study, published in the academic journal Environmental Pollution, takes the study of air pollution effects to the neighborhood level and quantifies the regional ecosystem services provided by urban trees.

The study’s findings will help inform discussions about how cities are designed, says Vivek Shandas, associate professor in PSU’s Toulan School of Urban Studies and Planning, and a leader of the Healthy Trees, Healthy People research project. “It also highlights potential environmental justice issues,” Shandas says, “as a majority of the most mature trees—the most valuable for reducing air pollution—are located in wealthy neighborhoods.” 

The research team also included Linda George, professor of environmental science; Todd Rosenstiel, associate professor of biology; Alexis Dinno, assistant professor of community health; and Meenakshi Rao, a School of the Environment Ph.D. candidate. 

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