Nobody pretends that polluted air isn't terrible for your health. Clean up the skies over any dirty city, and the people who live there will all but certainly become healthier. That, at least, has been popular wisdom, but until now, no one had ever put it to a statistical test. Now someone has, and the results are striking: according to a study just published in the New England Journal of Medicine, when local governments decide to scrub out the smog, local residents actually live an average of five months longer.
"It's very reassuring," says Dr. Douglas Dockery, one of the study's three authors and an environmental epidemiologist at Harvard's School of Public Health. "We can see some benefits from the regulations of air pollution that have been put in place in the past 20 to 30 years." (See pictures of the world's most polluted places.)
In order to reach so precise a finding, the study's authors had to do some exhaustive number-crunching, surveying pollution rates and longevity in 51 cities across the U.S. over a 21-year period from 1979 to 2000. Overall, they found that lifespan in all of the areas increased by an average of nearly three years from 74 to 77 as a result of a host of factors, most notably reduced smoking and improved income. But 15% of the change was attributable to cleaner air.
One of the reasons curbing pollution can have so immediate an effect is that even a little dirt can do a lot of damage. A reduction of just 10 micrograms (10 millionths of a gram) of pollution per cubic meter of air a degree of improvement many of the surveyed cities were able to attain during the two-decade-plus period could extend human lifespans a full nine months. How small is 10 micrograms per cubic meter? Consider that simply by living with a cigarette smoker, you're exposed to a daily dose of 20 to 30. Pittsburgh, Pa., is one city in the survey that was at the 30-microgram level before the decline of the steel industry in the 1980s drove the dirt out of the skies even as it drove jobs out of town. Pittsburgh was one of the biggest winners in the new study, with residents gaining roughly 10 months in life expectancy over what they had when the mills were still churning. (See pictures of the effects of global warming.)
How can researchers separate the role that improved air quality plays from other factors? Very carefully. "The problem is," says Dr. C. Arden Pope III, the study's lead author and an epidemiologist at Brigham Young University, "if you consider every factor that extends life expectancy and add them up, you almost always end up with more than a 100% improvement." This is because many of the factors overlap, so scientists must take care not to count an extra week, say, as an extra two or three weeks.
The benefits of cleaner air may even be felt in towns whose skies weren't that dirty to begin with. Those that began with the very lowest levels still saw health benefits from small improvements. The evidence isn't yet there to determine whether those benefits would continue growing until the fine-particle pollution got down to zero; one of the cities closest to that, Albuquerque, N.M., still hovers around 5 micrograms per cubic meter. But at this point, it doesn't seem that the benefits taper off. "If it continues to follow what we've observed, it appears that there are health benefits down to very low levels of exposure," says Pope. (See the Year in Health, from A to Z.)
The next step for both researchers and policymakers is determining which sources of dirt power plants, motor vehicles, other industrial polluters make the biggest contributions to particle levels and thus should be most aggressively targeted. "In a difficult economic situation," asks Dockery, "where can we spend the dollars that would have the most benefit?"
As with so many other things, the inauguration of President Barack Obama has people hoping that these kinds of questions will be more aggressively addressed than they were over the past eight years. Even during the most heated days of the fall campaign, neither candidate went so far as to promise longer life in exchange for a vote. But a smart environmental policy could deliver just that.