On December 14, 2012, EPA revised the National Ambient Air Quality Standard (NAAQS) for PM2.5 (fine particulate matter). The annual standard was reduced from 15.0 micrograms per cubic meter (ug/m3) to 12.0 ug/m3. The existing 24-hour PM2.5 standard, as well as existing PM10 standards, remain unchanged. In addition to the revised annual standard, EPA issued implementation provisions, including grandfathering of certain pending construction permits. Initial attainment/nonattainment designations are expected to occur in 2014, with final designations issued in 2015. EPA expects that most of the U.S. already meets the new standard and that 99% of counties will meet the new standard by 2010 without any additional local PM2.5 control measures.
For more information: http://www.epa.gov/pm/actions.html#dec12