While the rate of improvement of U.S. air quality has slowed during the last decade, even those small improvements have had a beneficial effect on life expectancy, according to new research. In a study of 545 counties across the U.S., researchers from the Harvard School of Public Health found that a slight decrease of fine particulate matter of 2.5 micrometers or less in diameter — known as PM2.5 — from 2000 to 2007 was associated with an average increase in life expectancy of 0.35 years. During that period, researchers say, concentrations of PM2.5 decreased by 10 micrograms per cubic meter. While that improvement in air quality was far less significant than the pollution reductions observed between 1980 and 2000, the new findings suggest that continued improvements have additional health benefits. “It appears that further reductions in air pollution levels would continue to benefit public health,” said Harvard researcher Andrew Correia, lead author of the study published in Epidemiology.