The new EPA Clean Air Standard, which was proposed in June and is consistent with the advice from the agency’s independent science advisors, sets the annual health standard at 12 micrograms per cubic meter and is based on an extensive body of scientific evidence that includes thousands of studies. Many of the large studies used by EPA to set the standard show negative health impacts from PM2.5 at lower levels than previously understood.

EPA also utilized extensive consultation with stakeholders, including the public, health organizations and industry, and after considering more than 230,000 public comments.

The new standard has no effect on the existing daily standard for fine particles or the existing daily standard for coarse particles (PM10), which includes dust from farms and other sources), both of which remain unchanged. By 2020, ninety-nine percent of U.S. counties are projected to meet EPA’s revised health standard without any additional actions.

“These standards are fulfilling the promise of the Clean Air Act. We will save lives and reduce the burden of illness in our communities, and families across the country will benefit from the simple fact of being able to breathe cleaner air,” said EPA Administrator Lisa P. Jackson, who in December announced that she would be leaving the agency.

Fine particle pollution can penetrate deep into the lungs and has been linked to a wide range of serious health effects, including premature death, heart attacks and strokes, as well as acute bronchitis and aggravated asthma among children. A federal court ruling required EPA to update the standard based on best available science. The new standard builds on steps already taken by EPA to slash pollution in communities across the country. Thanks to these steps, 99 percent of U.S. counties are projected to meet the standard without any additional action.

It is expected that fewer than 10 counties, out of the more than 3,000 counties in the United States, will need to consider any local actions to reduce fine particle pollution in order to meet the new standard by 2020, as required by the Clean Air Act. The rest can rely on air quality improvements from federal rules already on the books to meet this new standard.