On December 14, 2012, the U.S. Environmental Protection Agency (EPA) completed a review of the particulate matter standards to better protect public health and welfare. At that time EPA strengthened the level of the annual primary PM2.5, National Ambient Air Quality Standard (NAAQS) to 12.0 micrograms per cubic meter (ug/m3), retained the 15 ug/m3 standard as the annual secondary NAAQS, and retained the 24-hour fine particle standard of 35 (ug/m3) EPA also retained the coarse particle (PM10) standards. For more information, including a fact sheet on the revision, please visit U.S. EPA: Particulate Matter: Regulatory Actions .
The EPA has requested that Governors recommend attainment, unclassifiable, and non-attainment designations, as appropriate for all PM2.5 areas under their jurisdiction and submit these recommendations to U.S. EPA by December 13, 2013. The recommendations are based on such factors as sources of PM2.5 emissions and monitored particulate matter levels. U.S. EPA's promulgation of final designations is expected by December 12, 2014.