The study concluded that between the US population being exposed to much lower levels of air pollution than 30 years ago and reductions in fine particulate matter in the environment, there are fewer cardiopulmonary disease and mortality issues.
Researchers controlled for socioeconomic status, smoking prevalence, and demographics. They determined that a decrease of 10 micrograms per cubic meter during the 2000 to 2007 contributed to an increased life expectancy of 0.35 in 545 US counties.
Urban areas seem to be affected more strongly by reductions in fine particulate matter and increase in life expectancy. The particulate composition may be different between urban and rural areas.
Improved US policy enforcing stronger air quality controls has contributed to ambient air quality. This, coupled with reduced fine particulate matter and general awareness of the dangers of pollution have led to an improved quality of life and an increased life expectancy.