An interdisciplinary team of scientists from Portland State University (PSU) have found direct links between the presence of mature trees in a city and the air quality its citizens enjoy, uncovering new pathways to understanding the value provided by urban forests and the design of healthy cities.

The PSU Trees and Health team worked with numerous community volunteers, including many PSU and Washington State students, to place a web of 144 sensors across the greater Portland region. The scientists then examined neighborhood-specific air quality data correlated with detailed maps of Portland’s tree canopy, creating a new way to project and compare what its like to breathe in different corners of the city.

Then the researchers went a step further, calculating the total health-related respiratory benefit from Portland’s urban forest. The amount of nitrogen dioxide—an air pollutant that contributes to respiratory illnesses such as asthma—removed by the region’s trees amounts to $6.59 million per year saved by avoiding missed school and work days, emergency room visits, and hospitalizations.

The results of the study, published in the academic journal Environmental Pollution, is the first to take the study of air pollution effects to the neighborhood level and to quantify the regional ecosystem services provided by urban trees.

“This information will help us inform the discussion about how cities are built and how it matters to the people who live there,” said 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 as a majority of the most mature trees—the most valuable for reducing air pollution—are located in wealthy neighborhoods.”

This initial base of information will be used for further study by public health and environmental science research, and the team would like to see the study replicated across the country in order to help city leaders make informed decisions about city planning. While the easy answer to better air quality would seem to be “plant more trees,” some types of trees can create air quality problems through their own emissions.  The Trees and Health team scientists are drilling down into what types of trees are most beneficial in different urban settings.

The interdisciplinary Trees and Health team includes Shandas; 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.

About Portland State University (PSU)
Located in Portland, Oregon, PSU has about 30,000 undergraduate and graduate students. PSU’s motto is “Let Knowledge Serve the City,” and we provide every student with opportunities to work with businesses, schools and organizations on real-world projects. Our downtown campus exhibits PSU’s commitment to sustainability, and sustainability is incorporated into much of the curriculum. (

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