OK, so it's an average figure and there's lots more that goes into life expectancy calculations, but new research on the effects of declining air pollution in the United States is promising nevertheless.
The details, from the work of researchers from the Harvard School of Public Health, published in Epidemiology:
The study looked at the effects on health of fine particulate matter, small particles of 2.5 micrometers or less in diameter -- referred to as PM2.5. Numerous studies have shown associations between acute and chronic exposure to fine particle air pollution and cardiopulmonary disease and mortality. Studies have also shown that reductions in air pollution are associated with reductions in adverse health effects and improved life expectancy. Air pollution has been declining steadily in the U.S. since 1980, but the rate has slowed in the years since 2000. The HSPH researchers wanted to know whether the relatively smaller decreases in PM2.5 levels since 2000 are still improving life expectancy. (Science Daily
After controlling for a variety of factors (class, smoking, others), the results showed that the decreases in air pollution resulted in increased life expectancy of 4.2 months in the 545 counties examined.
Interestingly, there was a stronger association between declining air pollution in urban areas with increased life expectancy, along with a greater benefit for women than men. The scientists speculate that the composition of the air pollution in urban areas, while of the same size as rural areas, may make the difference.