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Portland Business Journal: How trees help Portland kids avoid missing 7,380 days of school
Author: Wendy Culverwell
Posted: August 28, 2014

Read the original story in the Portland Business Journal's Sustainable Business Oregon blog here

Portland’s urban canopy keeps kids in school, thwarts asthma attacks, curbs emergency room visits and helps elderly residents stay out of the hospital.

So says a unique study from Portland State University that set out to quantify just how trees in Portland improve air quality and reduce asthma-related events.

The study, published in the academic journal Environmental Pollution, was conducted by researchers collaborating across three departments at Portland State — the Department of Environmental Science and Management, the Department of Biology and the Nohad A. Toulan School of Urban Studies and Planning.

Collectively, the PSU Trees and Health research team deployed a series of 144 sensors across the region to measure nitrogen dioxide levels.

NO2 levels rise in tandem with traffic and industry and contribute to respiratory illnesses such as asthma.

Trees remove N02 from the atmosphere. The study concludes that even light tree cover of 20 percent has a measurable impact on NO2 levels and by extension, the respiratory health of the area’s residents.

The financial impact is considerable. The region’s existing canopy helped deter asthma and related episodes translating into a $6.59 million benefit in terms of lost school days, ER visits and hospitalizations.


Children ages 4 to 12 avoided missing 7,380 school days related to asthma attacks and had 21,466 fewer asthma-related episodes.

Residents of all ages avoided 54 asthma-related visits to local emergency rooms.

Residents ages 65 and over avoided 46 hospital stays due to respiratory illness.

The avoided incidents translate to a $6.5 million benefit, calculated in 2013 dollars.

The researchers say further study is needed to explore the relationship between urban forests and health benefits.

It also notes that N02-related health issues fall disproportionately on lower-income residents.

“Due to the geographic variation in the distribution of air pollutants in a city, the health impacts are not uniform and tend to be increasingly borne by susceptible and socially disadvantaged populations,” it said.

Citation: “Assessing the relationship among urban trees, nitrogen dioxide, and respiratory health.” Authors: Meenakshi Rao, Linda A. George, Todd N. Rosenstiel, Vivek Shandas and Alexis Dinno.

An abstract of the study is posted at the Environmental Pollution web site.