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March 11, 2009 -- Long-term exposure to ground-level ozone significantly increases the risk of death from respiratory problems, a new study shows.
A team of scientists says the risk of dying from respiratory problems is more than 30% greater in metropolitan areas with the highest ozone concentrations than areas where ozone levels were the lowest.
Ground-level ozone, along with particulate matter, is a major component of smog. Ozone is a naturally occurring gas most prevalent high in the atmosphere, where it protects against harmful ultraviolet rays of the sun. However, ozone at ground level is produced when exhaust from cars, power plants, and other sources reacts chemically in sunlight. According to the Environmental Protection Agency, ground-level ozone can irritate breathing, decrease lung function, inflame airways, and worsen lung conditions such as asthma and emphysema.
Previous studies have shown that long-term exposure to fine particulate matter -- tiny particles of dust and soot -- are a major risk factor for death from heart and lung disease.
But until now, it was unclear whether ozone was linked to a higher risk of death from lung disease itself, Michael Jerrett, PhD, tells WebMD. Jerrett is an associate professor of environmental health at the University of California-Berkeley and lead author of the study.
Now that’s no longer in question, he says.
“This is the first study to show that ozone, long considered a secondary pollutant, is a key cause of death,” he says. “This is the first time we’ve been able to connect chronic exposure to ozone with the risk of death.”
The study, published in the March 12 issue of The New England Journal of Medicine, followed 450,000 people from 1982 to 2000 and covered 96 metropolitan regions. Over the 18-year study period, 118,777 people died.
“The study presents evidence for the first time that long-term exposure to ozone and fine-particulate pollution have separate, independent effects on mortality, and that they seem to impact different parts of the body,” Jerrett tells WebMD.
The study also makes clear that controlling ozone would not only reduce deaths, but mitigate global warming, Jerrett says.
George D. Thurston, ScD, a professor of environmental medicine at New York University School of Medicine and a study co-author, says ozone tends to form in higher concentrations in suburbs and rural areas downwind of cities.
That’s due in part to commuting patterns, Jerrett says. It’s hard to keep counts down when governments at all levels can’t control sprawl and “one-person-per-car-commuting,” he says.