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Even low levels of air pollution may not be safe, a new study suggests.

The Environmental Protection Agency rates air pollution based on concentrations of particles smaller than 2.5 microns, or PM2.5. It generally regards as safe an annual average of 12 micrograms per cubic meter of air, or 35 micrograms per cubic meter over a one-day period.

Researchers studied all Medicare recipients in New England, using satellite data to rate short- and long-term exposure. They tracked daily air pollution from 2003 to 2008 and used Medicare data on residents older than 65 to calculate death rates. More than 550,000 people were included in the analysis, published in Environmental Health Perspectives.

Generally, E.P.A. standards were met. But each 10 microgram per cubic meter increase in PM2.5 was associated with a 2.14 percent increase in death rate over a two-day period, and a 7.52 percent increase over a year.

Even in rural areas like northern Maine, where the E.P.A. standard was consistently met, the results were similar. For each 10 microgram increase, there was a 2.14 percent higher death rate short-term, and 9.28 percent higher over a full year.

“The E.P.A. should tighten its standards,” said the lead author, Liuhua Shi, a doctoral student at the T.H. Chen Harvard School of Public Health, “and we need to reduce particles in the air, which we can do with off-the-shelf technologies.”