Trees are believed to save 870 lives a year and prevent 670,000 incidences of acute respiratory symptoms.
The study, conducted by the United States Forest Service and collaborators, was the first broad-scale estimate of air pollution removal by trees, the U.S. Department of Agriculture reported.
Trees remove about one percent of air pollution from the environment, but this makes a big difference. Their effect reduces air pollution by about $7 billion every year. Pollution removal is significantly higher in rural regions compared to urban areas, but cities seem to reap more health benefits.
"With more than 80 percent of Americans living in urban area, this research underscores how truly essential urban forests are to people across the nation," said Michael T. Rains, Director of the Forest Service's Northern Research Station and the Forest Products Laboratory. "Information and tools developed by Forest Service research are contributing to communities valuing and managing the 138 million acres of trees and forests that grace the nation's cities, towns and communities."
The study looked at four pollutants: nitrogen dioxide, ozone, sulfur dioxide, and particulate matter less than 2.5 microns in aerodynamic diameter. These are considered for Environmental Protection Agency (EPA) air quality standards. Health effects imposed by these pollutants include problems in the pulmonary, cardiac, vascular, and neurological systems. There are about 130,000 deaths related to particulate matter and 4,700 ozone-related deaths were estimated to have occurred in the year 2005.
"In terms of impacts on human health, trees in urban areas are substantially more important than rural trees due to their proximity to people," study co-leader Dave Nowak said. "We found that in general, the greater the tree cover, the greater the pollution removal, and the greater the removal and population density, the greater the value of human health benefits."
