A study on correlations between air quality and life expectancy is doing the rounds in a science press at the moment. The bottom line from their statistical analysis:
average life expectancy in 51 U.S. cities increased nearly three years over recent decades, and approximately five months of that increase came thanks to cleaner air.
Which doesn't seem unreasonable on the face of it: there's plenty of supporting evidence for the general thesis that air quality and longevity have some correlation. My caveat would be that any single study showing an effect of less than a year on human longevity should be taken with a grain of salt. Firstly that's certainly small enough to be either an artifact or due to some other, related correlation, and secondly it doesn't much matter in the grand scheme of things.
You can probably push your life expectancy a decade or more in either direction - 20 times as long as the variation in the paper - just by changing what you eat and the level of exercise in your life. Beyond that, progress in medical science has the potential to increase your healthy life span by a far greater number of years.
We don't have all the time in the world to make our future better, healthier, and longer. It's best to focus on what will have the greatest impact: everything else is a distraction.