December 18, 2012
Background Paper on Particulate Matter (PM) National Ambient Air Quality Standards (NAAQS)
Related Studies & Resources
Under Section 109 of the Clean Air Act (CAA), the U.S. Environmental Protection Agency (EPA) is required to issue national ambient air quality standards (NAAQS) for six air pollutants: ozone, nitrogen oxide (NOx), carbon monoxide (CO), sulfur dioxide (SO2), lead and particulate matter. EPA is required to issue both primary (health-based) and secondary (welfare-based) standards. EPA must review existing NAAQS and issue revised or new primary and secondary standards (as appropriate) every five years.
In October 2006, EPA published a final rule to revise the primary and secondary NAAQS for particulate matter (PM). In July 2007, it initiated the current review cycle for those NAAQS. Pursuant to court order, EPA issued its final rule on December 14, 2012.
The 2006 NAAQS for PM address fine particles (PM2.5), which are 2.5 micrometers in diameter or less, and inhalable course particles (PM10), which are less than 10 micrometers in diameter. A micrometer is 1/1,000th of a millimeter; there are 25,400 micrometers in an inch. The standards include an annual standard and a 24-hour standard and are expressed in terms of micrograms per cubic meter (µg/m3).
EPA’s final rule strengthens the PM 2.5 NAAQS, while retaining the existing standard for PM 10. EPA’s rule sets the PM 2.5 standard at 12 micrograms per cubic meter (µg/m3), a substantial strengthening of the current annual standard of 15 µg/m3, which has been in effect since 1997. EPA’s rule retains the existing 24-hour fine particulate standard (35µg/m3) which has been effect since 2006. EPA also is requiring changes to the monitoring network used to measure fine particle exposure on heavily traveled roads in areas with a population of 1 million or more. EPA anticipates making attainment/nonattainment designations by December 2014, with those designations likely becoming effective in early 2015. States would have until 2020 to meet the revised annual PM 2.5 health standards.
Potential Impact of RegulationDirect and indirect sources of fine particles include power plants, high-temperature industrial processes, e.g., steel mills and gasoline and diesel engines. Power plants, for example, emit SO2 and NOx, which contribute to the formation of fine particles. Revisions to existing NAAQS for PM may require more stringent controls on emissions from power plants (which may incur considerable compliance costs relating to the final rule on national emissions standards for hazardous air pollutants for power plants) and industrial facilities. Under the CAA, however, EPA may not take compliance costs into consideration when it issues NAAQS. EPA has estimated that compliance with this final rule will cost between $53 million to $350 million annually.