Clean air doesn't just give Americans a pleasant, smog-free view. It's added an average of five months to our lives.

In a study of three decades of health data from 51 U.S. cities, researchers found that people are living about three years longer than they did before. Controlling for changes in income, education, demographics and smoking, about five months of that can be chalked up to air improvements.

"Our efforts in the past 20 years to reduce air pollution through better technology and regulation have actually worked," said Majid Ezzati, an international health expert at the Harvard School of Public Health. "People are living longer as a result of it."

Along with Harvard environmental epidemiologist Douglas Dockery and Brigham Young University economist C. Arden Pope, Ezzati tracked the drop of what are known as PM2.5s — pollutant particles with a diameter of 2.5 microns, or 1/25 the diameter of a human hair.

During the 1980s and 1990s, average PM2.5 levels in the 51 cities dropped from 21 to 14 micrograms per cubic meter. A 10μg drop, calculated the researchers, produced a seven-month increase in life expectancy. The research was published Wednesday in the New England Journal of Medicine

Their estimates are necessarily rough, but track with similar findings in Canada, Finland and the Netherlands, where a 10μg reduction in pollution produced life extensions of between .80 and 1.37 years.

Ezzati declined to speculate on whether the Bush administration's approach to air pollution, criticized as being lax and industry-friendly, would reverse some of these gains.

Instead he stressed the principle at stake. "Rather than just saying pollution is bad for health," he said, "we can say that regulations are good for health."

"This finding provides direct confirmation of the population health benefits of mitigating air pollution," wrote Daniel Krewski, CEO of Risk Sciences International, in an editorial accompanying the study.

Citation: "Fine-Particulate Air Pollution and Life Expectancy in the United States." By C. Arden Pope III, Majid Ezzati and Douglas W. Dockery. New England Journal of Medicine, Vol. 360 No. 4, Jan. 21, 2009.

Image: Flickr/Sean McGrath

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