Don: Time to go again to the A Moment of Science mailbag. A listener writes:

     Dear Yaël and Don,
     I know that it's important to have clean air, but why? Besides making the air smell      better, what's the advantage of reducing air pollution?

Yaël: Interesting question. There are many reasons why reducing air pollution is      important. For example, several studies over the past few years have linked higher      levels of air pollution to putting people at greater risk for heart disease.

D: But maybe the clincher is that decreasing air pollution appears to actually increase      human life expectancy. A study by researchers at the University of Utah looked at air      pollution statistics collected from more than sixty cities across the United States from      1979 to 1983, and then again from 1999 to 2000. The researchers also looked at      life expectancy during the same periods.

Y: By 2000, Americans were living an average of nearly three years longer than they      had twenty years earlier. The researchers considered other factors, including      fewer people smoking cigarettes, changes in income and improvements in health      care. But less air pollution played an important role, too, accounting for around five      months of the life expectancy increase.

D: The finding is important because, as our listener's question suggests, the positive      effects of cleaning the air aren't always clear. The Utah study paints a pretty clear      picture: the cleaner our air, the longer we live.  

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