Regulation Database – Non-GHG Emission Standards

In 2015, based on EPA’s review of the air quality criteria for ozone (O3) and related photochemical oxidants and for O3, EPA revised the levels of both standards. EPA revised the primary and secondary ozone standard levels to 0.070 parts per million (ppm), and retained their indicators (O3), forms (fourth-highest daily maximum, averaged across three consecutive years) and averaging times (eight hours).

While EPA did not quantify the greenhouse gas reduction co-benefits of this rule, it did recognize in an implementation memo that sources of ozone pollution may generate GHG emissions (e.g., motor vehicles) and thus actions to reduce ozone pollution will also have GHG co-benefits.

In May 2011, EPA proposed National Emission Standards for Hazardous Air Pollutants (NESHAP) for coal and oil-fired electric utility steam generating units, commonly referred to as the Mercury and Air Toxics Standards (MATS) rule, which would require facilities to achieve an emissions rate for mercury and air toxics consistent with the implementation of the maximum available control technology (MACT). As part of the same rulemaking, EPA also proposed New Source Performance Standards (NSPS) for criteria pollutants (PM, NOx, and SO2) from fossil fuel-fired electric utility, industrial, commercial, and institutional steam generating units.

The final MATS / NSPS Rule was published in February 2012. Responding to an industry challenge, EPA revised certain aspects of the rule in April 2013 to soften standards for new power plants. In November 2014, EPA revised certain aspects of the rule pertaining to startup and shutdown standards. In April 2016, EPA issued technical corrections to the rule.


In Michigan v. EPA, 135 S.Ct. 2699 (2015), the U.S. Supreme Court ruled that EPA had improperly failed to consider compliance costs at the outset of developing the MATS Rule. The rule remained in effect pending remand to EPA, and in April 2016, EPA issued a supplemental finding considering compliance costs and concluding that the MATS Rule was appropriate and necessary.

Rule Documents:

In August 2011, EPA published the final Cross-State Air Pollution Rule (CSAPR). The rule replaced EPA’s 2005 Clean Air Interstate Rule (CAIR). The rule establishes a regulatory framework for reducing interstate sulfur dioxide (SO2) and nitrogen oxide (NOx) emissions from power plants in “upwind” states that contribute to non-attainment with, or impaired maintenance of, National Ambient Air Quality Standards (NAAQS) for ozone and fine particulate matter (PM2.5) in “downwind” states. In December 2011, EPA supplemented the final rule to cover additional states for certain pollution. EPA has also issued minor revisions to the rule’s compliance deadlines since it has been finalized. As of January 2017, the CSAPR requires 28 states in the eastern United States to reduce power plant emissions of SO2, annual NOX, and ozone season NOX affecting downwind states.

The U.S. Supreme Court upheld the CSAPR in EPA v. EME Homer City Generation, L.P., 134 S. Ct. 1584 (2014), reversing the D.C. Circuit Court of Appeals’ 2012 overturn of the rule. With the litigation ended, EPA began implementing Phase I of the CSAPR in 2015. EPA is scheduled to begin implementing Phase II in 2017, which would require certain states to make additional reductions in SO2 emissions.

In September 2016, EPA finalized Federal Implementation Plans (FIPs) in the CSAPR Update to address air quality impacts of the interstate transport of ozone air pollution in the eastern United States.

Rule Documents:

In March 2011, EPA promulgated national emission standards for hazardous air pollutants (NESHAPs) from three major source categories: industrial boilers, commercial and institutional boilers, and process heaters. The emission standards reflect the maximum achievable control technology (MACT) for control of mercury, hydrogen chloride, particulate matter, and carbon monoxide from coal-fired, biomass-fired, and liquid-fired major source boilers.

Upon reviewing reconsideration requests for the 2011 rule, in January 2013, EPA published a revised rule adjusting emission limits for different types of units subject to the regulations (some more stringent, some less), and establishing an alternative emission standard for carbon monoxide. After receiving further reconsideration requests, in November 2015, EPA published a new final rule making changes to the definitions pertaining to unit startup and shutdown. The new rule also made certain technical corrections to the previous rule.

In March 2011, EPA also published NESHAPs for two area source categories: industrial boilers and commercial and institutional boilers. The rule requires MACT for control of mercury and polycyclic organic

matter emissions from coal-fired area source boilers, and requires generally available control technology (GACT) or management practices for control of hazardous air pollutants emissions from biomass-fired and oil-fired area source boilers. In February 2013, EPA responded to reconsideration requests with a new rule revising compliance dates and making certain technical corrections. In September 2016, EPA responded to further reconsideration requests by revising: the alternative particulate matter (PM) standard for new oil-fired boilers; performance testing for PM for certain boilers; and fuel sampling for mercury for certain coal-fired boilers. EPA also made certain technical corrections in this final rule.

EPA regulates nine pollutants (particulate matter, carbon monoxide, dioxins/furans, sulfur dioxide, nitrogen oxides, hydrogen chloride, lead, mercury, and cadmium) from four types of incinerators (municipal solid waste; hospital, medical and infectious solid waste; commercial and industrial solid waste; and other solid waste). In March 2011, EPA published a final rule revising standards applicable to these incineration facilities: NSPS and emission guidelines for existing sources. In February 2013, EPA made certain technical and clarifying amendments. In June 2016, EPA made further minor amendments. In January 2017, EPA proposed a federal plan to implement emission guidelines in states without an approved state plan to implement the guidelines.

Regulation on Use of Science at EPA

Deregulatory Action: In April 2018, EPA proposed the Strengthening Transparency in Regulatory Science Rule, which would restrict EPA to relying only on scientific research for which the underlying data has been made available to the general public. Commenters warned that researchers are often unable to share the confidential information of participants in public health studies. In the revised proposal, EPA offers two alternatives: 1) prohibiting EPA from relying on studies for which the underlying data is not available for validation; or (2) allowing EPA to use such studies, but giving them lesser weight than those for which the underlying data is available. EPA is seeking comment on which approach should be adopted.

On January 5, 2021, EPA finalized a rule to limit the use of scientific studies for which underlying data is not publicly available. The final rule applies to scientific data that the agency uses in crafting regulations as well as all "influential scientific information" at the agency, a broad term that could apply to informal guidance or other agency actions.


Revised Clean Air Act Cost-Benefit Analysis

On December 9, 2020, the EPA finalized a rule to create standard practices for analyzing new regulations' costs and benefits under the Clean Air Act. The rule could be used to limit the agency's consideration of co-benefits when developing and justifying new regulations. This could constrain the agency's ability to consider climate regulations' ancillary benefits, such as reductions in conventional pollutants like soot.