"Americans are living longer because the air they breathe is getting cleaner, a new study suggests. The average drop in pollution seen across 51 metropolitan areas between 1980 and 2000 appears to have added nearly five more months to people's lives, according to a study published Wednesday in The New England Journal of Medicine."
http://www.cnn.com/2009/HEALTH/01/21/healthmag.airpollution.lifespan/index.html This is pretty cool. I'm skeptical about how they were able to filter out all the other potential causes for the improvement in lifespan, but in any case it's very good news.