Ozone, when it's high in the atmosphere, is great at shielding us from radiation—thus the concern about the ozone hole. But ozone down at our level, formed when organic compounds such as vapors from gas pumps react with sunlight, may cause health problems. Researchers at Yale and Johns Hopkins universities looked at ozone exposure and mortality.

What the researchers wanted to know: Does a short-term rise in ozone increase death rates?

What they did: The researchers used data on deaths in 95 urban areas from the National Center for Health Statistics and combined it with the Environmental Protection Agency's database of air quality. Ozone tends to be particularly high in the summer in urban areas, when there's plenty of sun.

What they found: On average, an increase in ozone of 10 parts per billion over six days led to a 0.52 percent increase in mortality on the next day. Yes, that's an increase of less than 1 percent, but it's still statistically significant and suggests that elevated ozone kills some people. For a sense of what a 10-ppb increase means, the EPA's ambient air quality standard for ozone is 80 ppb. Oh, and if you needed another reason to move to Honolulu, it had the lowest ozone concentrations of the cities studied.

What the study means to you: If this study is correct, an increase in ozone kills people.

Caveats: This study focused on urban areas; rural areas may have ozone problems sometimes, too. Also, the researchers don't know whether they're measuring the effect of ozone specifically, or whether ozone is just one pollutant standing in for a bigger pollution problem or representing a different pollution.

Find out more: Information from the EPA on ozone and health: www.epa.gov/O3healthtraining/population.html

Read the article: Bell, M.L. et al. "Ozone and Short-term Mortality in 95 U.S. Urban Communities, 1987–2000." Journal of the American Medical Association. Nov. 17, 2004, Vol. 292, No. 19, pp. 2372–2378.

Abstract online: http://jama.ama-assn.org