O is for ozone. D is for death.

By David Steinkraus

Wednesday, November 17, 2004 2:05 AM CST

Study finds that even a little ozone can kill In the annual rankings of air quality, southeastern Wisconsin commonly receives an F. A study published today suggests that grade should be a D - for death.

In an examination of how ozone affects the death rate, a team of researchers concluded that an increase of just 10 parts per billion in the ozone concentration increased the daily death rate by about one-half percent in 95 urban areas.

This indicates a substantial health cost from ozone, the authors write in today's issue of the Journal of the American Medical Association. They estimate 3,767 premature deaths annually in those 95 communities. Moreover, they write, this doesn't take into account all effects of ozone.

The study addressed only the effects of ozone exposure from day to day. What it doesn't measure are the deaths that may result from a lifetime of exposure, said Francesca Dominici, 35, one of the paper's co-authors and an associate professor of biostatistics in the School of Public Health at Johns Hopkins University.

"So we're not saying that ozone two weeks ago does not have an impact," said Michelle Bell, 34. She is the lead author on the paper and is an assistant professor at the Yale University environment school.

Ozone is formed by the interaction of nitrous oxides in smog with oxygen in the atmosphere. In the presence of sunlight these form ozone, an unstable molecule of three oxygen atoms that irritates lungs and eyes. Much of the smog in urban areas comes from automobile exhaust, hence the emissions testing that is mandated by Wisconsin and other states.

This study is one of the largest ozone pollution studies ever conducted, Dominici said. Unlike previous studies, which focused on single cities, this one applied the same methods to information from all over the country.

The study also found that it isn't just the elderly or very ill who are most susceptible. The effect was similar for all age groups, Bell said. "That means that everyone needs to be concerned about ozone and mortality, even young healthy adults."

There are steps which the researchers are planning now. First will be exploring whether there's a threshold, an ozone concentration below which there's no harm, "which is very timely for environmental policy," Dominici said.

The U.S. Environmental Protection Agency, which is in the process of reviewing its ozone standard, sponsored the study, Bell said.

Another step will be to look at some of the differences they found. For example, Los Angeles, a place where cars rule and smog blankets the surrounding mountains starting in early summer, showed a smaller death increase due to ozone than Milwaukee. Deaths due to ozone also increased more in Madison than Milwaukee, and more still in Chicago.

What's important, Bell said, is the demonstration of incremental harm. Increase the ozone levels and deaths increase. Increase ozone more, and there are even more deaths.

"We're saying that every little bit of ozone is harmful for you, and every little bit you decrease is beneficial."

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