Trees save 870 lives a year and prevent 670,000 incidences of acute respiratory symptoms, according to a new study.

The study was conducted by the United States Forest Service and collaborators. It is the first broad-scale estimate of air pollution removal by trees, the U.S. Department of Agriculture reported in a press release.

Trees remove approximately one percent, or $7 billion, in air pollution from the environment every year.

Pollution removal is higher in rural regions compared to urban areas, but cities still seem to enjoy the 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, according to the release. "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."

For the study, researchers looked at four pollutants: ozone, sulfur dioxide, nitrogen dioxide, and particulate matter less than 2.5 microns in aerodynamic diameter.

These are considered for Environmental Protection Agency (EPA) air quality standards.

Problems in the pulmonary, cardiac, vascular, and neurological systems can occur due to these pollutants.

About 130,000 deaths have occurred relating to particulate matter and 4,700 ozone-related deaths occurred in 2005, according to the study.

 "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, according to the release. "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."

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