Just how bad is air pollution for you? A study of more than 60 million Medicare recipients has found that even pollution levels below those generally considered safe increase the risk for premature death.

Using satellite, meteorological and other data, plus data gathered from 3,805 monitoring stations maintained by the Environmental Protection Agency, researchers were able to accurately estimate daily air pollution levels nationwide. The study is in The New England Journal of Medicine.

They followed the population for a median of seven years, recording 22,567,924 deaths. They found that each increase of 10 micrograms per cubic meter in particles smaller than 2.5 microns, or PM 2.5, was associated with a 7.3 percent increased mortality, and each increase of 10 parts per billion in warm-weather ozone was linked to a 1.1 percent increase.

Average PM 2.5 ranged from 6.21 to 15.65 over the study period; a level of 12 is considered tolerable. Warm-season ozone concentrations ranged from 36.27 to 55.86; a level of 70 is thought to be safe.

“When you have a large study that shows that the current level of air pollution is toxic — I hope that’s something we can do something about,” said one author, Francesca Dominici, a professor of biostatistics at Harvard.