A study of 60 million Americans over the age of 65 estimates that thousands of people are still dying prematurely each year because they are breathing polluted air.

The study, conducted by researchers at Harvard’s T.H. Chan School of Public Health, said these premature deaths are occurring in areas where air pollution levels are lower than federal National Ambient Air Quality Standards. The study, published in the New England Journal of Medicine, said that even a modest reduction in what are known as PM2.5 pollution particles — those measuring less than 2.5 microns — could prevent about 12,000 premature deaths annually.