Even slight increases in low-level ozone pollution cause death rates for heart and lung disease to rise, researchers with the Johns Hopkins Bloomberg School of Public Health conclude in the first national study to document a connection between the pollutant and deaths.
A roughly 35 percent reduction in daily ozone levels nationally would save almost 4,000 lives a year, author Francesca Dominici and four colleagues write in an article published in today's Journal of the American Medical Association.
"Ozone is a national problem. But there are lots of things we could do to reduce ozone pollution, including driving less, carpooling more, creating more mass transportation and adding technology to reduce pollution from power plants and industrial sources," said co-author Michelle L. Bell, who worked at Johns Hopkins until January, and is now an assistant professor at Yale University.
The report, based on examination of death rates and pollution levels over 14 years in 95 U.S. cities, including Baltimore, is the first to provide convincing evidence that even levels of ozone considered healthy by the federal government are dangerous, said Arden Pope, a professor at Brigham Young University who specializes in air pollution.
"This study is troubling, because it suggests that even if we are fully in compliance with EPA ozone standards, we would have negative impacts on our health," said Pope, who did not participate in the Hopkins study. "On the other hand, it suggests that even small improvements in ozone levels will save lives."
Ozone is a odorless, colorless gas that forms when pollutants from smokestacks and vehicle tailpipes blend on hot, sunny days.
Ozone levels nationally have been generally declining over the past 30 years, in part because of improving emission controls on cars and industry. But 474 of the nation's 3,000 counties and cities - including the Baltimore area - still don't meet the Environmental Protection Agency's health standards for ozone, affecting 159 million inhabitants.
Previous studies have shown that high levels of ground-level ozone cause coughing and wheezing, and can trigger asthma attacks. Researchers also have found that microscopic soot particles can cause heart attacks and retard the growth of children's lungs.
The EPA requested and paid for the Hopkins study, and will examine its results as it decides whether to change what it considers safe levels of ozone, said John Millett, an EPA spokesman.
"We have suspected a link ... but this study provides new evidence indicating that ozone is associated with increased death rates," Millett said.
In an attempt to combat the problem, the EPA is expanding pollution credit trading programs that provide financial incentives for power plants and industries to reduce pollution.
California has the worst ozone pollution among the 50 states, followed by Texas, Ohio, Pennsylvania and Michigan, according to a September report by the U.S. Public Interest Research Group, a Washington-based nonprofit organization. Maryland ranked 16th, with its ozone levels exceeding federal health standards 57 times last year, according to the report, which uses state and federal air pollution data.
William D. Fay, president of a power industry-funded group called the Foundation for Clean Air Progress, questioned the significance of the Hopkins report and said there "is some uncertainty" in the connection between ozone and deaths.
But the authors said the reams of mortality and air pollution data they examined spanning 1987 through 2000 for America's largest urban areas suggest "strong evidence of an association between mortality and short-term exposure to ozone."
After eliminating deaths from accidents, injuries, traffic accidents, heat and other causes not linked to air pollution in a city, the authors found that for every increase in ozone levels by 10 parts per billion, daily death rates there rose by half a percentage point. The deaths are often caused by heart or lung failure, the study says.
The federal standard for healthy ozone levels is 80 parts per billion over an eight-hour period, which is the equivalent of 60 parts per billion over a 24-hour period.
New York City had an average daily ozone level of 20 parts per billion from 1987 to 2000, but it ranged from zero to 81 parts per billion over a 24-hour period. Every increase of 10 parts per billion corresponded to an additional 319 annual deaths in that city, according to the report.
"Small increases in ozone are associated with small increases in mortality; large increases in ozone are associated with large increases in mortality," Bell said.