THURSDAY, June 27 (HealthDay News) -- Parks and tree-lined streets may give city dwellers more than shade. They may also save some lives, a new study from the U.S. Forest Service suggests.
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Researchers estimate that across 10 U.S. cities, "urban forests" prevent an average of one death per year, by helping to clear the air of fine particulate matter -- tiny particles released when fossil fuels are burned. Car exhaust, wood burning and industrial sources such as power plants all contribute.
Those fine particles can be inhaled deeply into the lungs, and they are a particular concern when it comes to people's health, said David Nowak, a Forest Service researcher who led the study.
The particles are thought to cause inflammation in the blood vessels and airways, which can be dangerous for people with existing heart or lung disease.
The new findings, reported in the July issue of the journal Environmental Pollution, suggest that trees play a role in protecting urban dwellers from the health effects of air pollution.
But, Nowak said, it's not just a simple matter of "let's plant more trees."
This study shows a "large-scale" correlation between tree coverage and human health. But researchers still have to figure out the nitty-gritty, Nowak said. "How do we best design to protect people from [fine particle pollution]? What configuration of plants do we need? What species of tree?" he said.
And all of that, Nowak added, has to be figured out at the local and regional levels.
Trees, he noted, do a lot more than clear fine particles from the air. They have many beneficial effects -- including reducing other air pollutants such as ozone, and keeping the temperature down during the summer. But certain other effects are not so good for human health: Trees release pollen, for example, which can exacerbate allergies and asthma.
"We need to make smart decisions about what we should plant, where we should plant and when we should plant, in order to improve people's quality of life," Nowak said.
The findings are based on daily air-quality data from 10 U.S. cities, along with information on the cities' tree coverage. To gauge how trees might be affecting city residents' health, Nowak's team used a computer program from the U.S. Environmental Protection Agency (EPA) that estimates the health impact of changes in air quality.
Overall, Atlanta was number one when it came to the amount of fine particle pollution removed by trees, at 64.5 metric tons -- owing to the city's relatively dense urban forest.
But as far as lives saved, New York City came in on top, with an average of eight lives saved per year. That, Nowak said, was partly due to the city's large population, but also to the "moderately high" removal of fine particles from the air -- thanks to trees.
No one is claiming that trees are the answer to air pollution, though.
Trees may be a smaller-scale way to give people extra protection from pollution, said Janice Nolen, assistant vice president of national policy for the American Lung Association.
"But they're not going to be the solution," Nolen said.
The "big tools," she said, are measures to reduce emissions from power plants, cars and other sources of pollutants.
One of those wide-scale measures got extra attention this week. The U.S. Supreme Court on Monday agreed to review a controversial decision by the D.C. Circuit Court of Appeals that reversed a major EPA air-quality policy -- dubbed the Cross-State Air Pollution Rule, the Washington Post reported.
The regulation would have cut emissions from coal-fired power plants across more than half of U.S. states. Last August, the D.C. Circuit Court said the EPA had overstepped its authority in issuing the rule.
"We're very pleased the Supreme Court will review this," Nolen said.
As for trees, she said they are a worthy pollution-fighting measure to keep studying -- including whether strategic planting along roadways might be beneficial.
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SOURCES: David J. Nowak, Ph.D., urban forests, human health, and environmental quality unit, U.S. Forest Service, Syracuse, N.Y.; Janice Nolen, assistant vice president, national policy, American Lung Association; June 24, 2013, Washington Post; July 2013, Environmental Pollution
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