The U.S. EPA issued a final rule for states to use in creating their plans to address particulate matter pollution, including new due dates for attainment and plan submissions and information on how to demonstrate compliance.

The July 29 publication addresses current and future National Ambient Air Quality Standards for fine particulate matter, which sets limits on emissions of that pollutant. Particulate matter can be emitted directly from a source, such as unpaved roads or construction sites, which the EPA regulates through the primary NAAQS for the pollutant, but can also be formed in the air due to a chemical reaction after certain pollutants are emitted from sources such as power plants.

The EPA regulates this particulate matter as the secondary standard, referring to the chemicals necessary for the reaction as "precursors." Power plants are among the leading sources of the precursor pollutants.

Also on July 29, the U.S. Court of Appeals for the District of Columbia Circuit issued a decision related to the issues addressed in the rule, but the EPA confirmed in an Aug. 2 email that the decision and the rule release will have no impact on each other.

The D.C. Circuit in 2013 remanded the EPA's NAAQS for particulate matter back to the agency, finding that the standards were set under an incorrect section of the Clean Air Act. The EPA responded by issuing the PM2.5 Deadline and Classification Rule in April 2014 under the correct section of the act, which was the underlying rule at issue in the July 29 court decision, the agency said.

The final rule issued the same day also responds to the remand by finalizing planning requirements for states with areas that do not meet the 1997 and 2006 particulate matter standards, as well as for the 2012 standards. The agency said states that do not meet the standards addressed in the new rule will now have to develop plans, and the new rule offers guidance on how to demonstrate compliance. Those plans must be completed within 18 months of being designated as out of attainment with the NAAQS consistent with the corrected Clean Air Act section.

The new guidance applies to current areas deemed nonattainment and future regions that receive such a designation. The final rule selects the precursor pollutants — sulfur dioxide, nitrogen oxides, volatile organic compounds and ammonia — which will need to be controlled in most circumstances. But the rule also gives states a chance to demonstrate that a particular pollutant is not contributing to the exceedance of particulate matter pollution in a given nonattainment area.

There are two classes of attainment designations, moderate and serious, and the EPA has now clarified the process of reclassifying areas from moderate to serious. The agency is revoking the original 1997 primary standard for areas designated as attainment because the agency revised that standard in 2012. The particulate matter NAAQS were reviewed and revised in 2006 and most recently in 2012.

Finally, the rule addresses new source review permitting, defining major sources and major stationary sources of particulate matter precursor pollutants and designating significant emissions rates of these precursors that would apply for modifications of existing major stationary sources.