07/15/2020 - Regulatory Tracker

National Ambient Air Quality Standards for PM and Ozone

by EELP Staff

Click here to return to EELP’s Regulatory Rollback Tracker. While this is a Trump-era tracker, we continue to update these entries with early Biden administration actions. We are also developing new resources on the Biden administration available on our Environmental Governance page. If you’re a reporter and would like to speak with an expert on this rule, please email us.

Why it Matters

EPA sets National Ambient Air Quality Standards (NAAQS) for six common and harmful pollutants: carbon monoxide, lead, particulate matter (PM), ozone, nitrogen dioxide, and sulfur dioxide. The NAAQS are based solely on public health and welfare protection, meaning that the agency must not consider the cost of revising a standard if the current science demands a standard be tightened to protect public health or welfare. The NAAQS program is highly successful and is the cornerstone of EPA’s work to protect public health and the environment. EPA estimates that in the past 40 years, total emissions of the six pollutants regulated by NAAQS dropped by 71% while the economy grew by 182%.

The Clean Air Act requires that EPA review the NAAQS every five years to ensure their adequacy. The review process is a multi-stage, robust review of the current science that requires significant expert input. If a standard is tightened, there is a cascading effect on air quality policies and programs across the country. States and local regions must ensure that the sources of pollution in their jurisdiction decrease their emissions, so that the region can meet the new, more stringent national standard.

For more information on changes to the NAAQS review process under this administration, visit the public health section of our EPA Mission Tracker.

For more information on the implementation of the 2015 ozone standards, EPA’s attainment designations, and challenges to those determinations, see our Rollback Tracker page, 2015 Ozone National Ambient Air Quality Standards.

Current Status

Under former President Trump, EPA issued two final rules refusing to update the NAAQS for particulate matter (PM) and ground-level ozone. Multiple coalitions of environmental organizations and states have now sued EPA challenging both rules. The Biden administration also issued an Executive Order on Day 1 requiring EPA to review both the ozone and PM NAAQS rules. Multiple organizations and states have since challenged both the PM and ozone NAAQS rules. On June 10, 2021, EPA announced it was beginning the process of reconsideration of the Trump administration decision not to strengthen PM standards and expects to issue a proposed rule in Summer 2022.


Jan. 15, 2013 EPA concludes its 2012 review of the PM NAAQS and determines that the existing standards inadequately protect public health. EPA tightens annual health-based standards for fine particles (PM2.5) to 12.0 micrograms per cubic meter. EPA estimates that the benefits of the revised standards will be between $3.6 and $9 billion.

Dec. 3, 2014 EPA announces the beginning of its next review of the PM NAAQS by issuing a call for information to assist EPA in developing the Integrated Science Assessment.

Oct. 25, 2015 EPA concludes its review of the ozone NAAQS and determines that the existing standards inadequately protect public health and welfare. EPA tightens the health-based and welfare-based standards to 0.070 parts per million.

Dec. 2016 EPA releases the final review plan for the PM NAAQS review. EPA projects that the scientific review will be completed in Fall 2020 and a final decision made on the NAAQS in 2022.

Trump Era

Oct. 31, 2017 Administrator Pruitt issues a memo changing the membership requirements for the Clean Air Science Advisory Committee (CASAC). CASAC is an independent expert committee that assists EPA in reviewing the NAAQS. Under the new guidelines, scientists who have received grants from EPA are no longer eligible to serve on the committee.

April 16, 2018 President Trump issues a memo ordering the EPA Administrator to reexamine the NAAQS review process and develop criteria to “ensure transparency” regarding scientific evidence used in that process. The memo also requires EPA, when issuing any final NAAQS rule, to concurrently issue rules and guidance to implement those standards.

June 26, 2018 EPA announces the beginning of its next review of the ozone NAAQS by issuing a call for information to assist EPA in developing the review plan and science assessment.

May 9, 2018 Administrator Scott Pruitt signs a Memorandum, Back-to-Basics Process for Reviewing National Ambient Air Quality Standards, which modifies and accelerates the process for reviewing and setting the NAAQS. The memo directs the agency to complete the current reviews of the ozone NAAQS by October 2020 and the PM NAAQS by December 2020. Many experts argue that this schedule is incompatible with the thorough scientific review required by the Clean Air Act.

Oct. 10, 2018 EPA issues a press release tasking CASAC with reviewing the ozone and PM NAAQS, notably eliminating the role of independent review panels that were historically convened to assist CASAC. The PM panelists report receiving a dismissal email from EPA. These expert panels are essential to a robust scientific review, given that CASAC has – by consequence of being a seven-member panel – limited expertise.

Oct. 23, 2018 EPA announces the public comment period for the draft Integrated Science Assessment for PM.

Dec. 10, 2018 Three current CASAC members urge EPA to reconvene the Ozone Review Panel in their comments on the draft Integrated Review Plan for Ozone NAAQS.

April 11, 2019 CASAC writes a letter to Administrator Wheeler critiquing the Draft Integrated Science Assessment for PM. CASAC advises EPA to develop a Second Draft Integrated Science Assessment for the committee to review and to reappoint the disbanded PM panel. CASAC specifically seeks additional expertise in diverse scientific fields to ensure that “meaningful independent scientific review” can occur.

Aug. 22, 2019 EPA publishes the Integrated Review Plan for the Review of the Ozone NAAQS, which includes a timeline projecting that EPA will finalize the Ozone NAAQS in “Winter 2020/2021.” EPA does not include a plan to develop a Risk and Exposure Assessment and instead plans to include the relevant analysis in the Policy Assessment. The Risk and Exposure Assessment is a separate scientific assessment that builds upon the conclusions of the Integrated Science Assessment. EPA has historically made the Risk and Exposure Assessment available for public comment and sought CASAC’s review of the document independently from other assessments.

Sep. 5, 2019 EPA releases the draft Policy Assessment for PM NAAQS. The Policy Assessment states that the available evidence and analyses “can reasonably be viewed as calling into question the adequacy of the public health protection afforded by” the PM2.5 standards.

Sep. 13, 2019 EPA announces the selection of 12 consultants to answer individual questions passed through the CASAC chair from CASAC members regarding the review of the NAAQS for ozone and PM. The use of consultants, rather than an independent panel, severely reduces transparency and effectiveness of the review process by not allowing for an open debate among and deliberation by experts meeting together.

Sep. 26, 2019 EPA publishes the draft Integrated Science Assessment for Ozone, which will be discussed at the December 2019 CASAC meeting.

Oct. 22, 2019 The Independent Particulate Matter Review Panel, which comprises 18 former members of the now-disbanded PM Review Panel, submit consensus recommendations to CASAC ahead of its October meeting. The independent panel recommends tightening the PM NAAQS in order to meet the Clean Air Act standard of adequately protecting public health. This report follows a two-day meeting by the group, which sought to closely mirror the meeting they would have had if EPA had not disbanded the panel.

Oct. 31, 2019 EPA releases the draft Policy Assessment for the Ozone NAAQS before CASAC has reviewed and sought revisions to the science assessment. The Policy Assessment finds that the newly available evidence continues to support the current ozone NAAQS. The Policy Assessment is also slated for discussion at the December 2019 CASAC meeting.

Nov. 13, 2019 CASAC releases a draft report following its October meetings. The report recommends EPA retain the current PM NAAQS but acknowledges that CASAC did not reach a consensus on this recommendation.

Dec. 2, 2019 18 former members of the CASAC Ozone Review Panel send a letter to EPA stating that the changes EPA has made to the NAAQS review process  “are collectively harmful to the quality, credibility, and integrity of EPA’s scientific review process and to CASAC as an advisory body.” The letter goes on to state that “[t]he NAAQS review for ozone should be suspended until these deficiencies are corrected.”

Dec. 3-6, 2019 CASAC meets to discuss the Integrated Science Assessment and Policy Assessment for Ozone as well as the Policy Assessment for PM.  Reviewing the ozone science and policy assessments together decreases the level of review possible by CASAC and departs from the previous long-standing NAAQS process of determining the science before considering policy.

Dec. 3, 2019 CASAC votes to approve an updated version of the Nov. 13 report that recommends EPA retain the current PM NAAQS. The report makes clear that this recommendation does not reflect a consensus among CASAC members, meaning that not all members agree that the current PM NAAQS adequately protect public health.

Dec. 6, 2019 CASAC fails to reach consensus regarding the adequacy of the existing ozone NAAQS. Six members endorse retaining the current standards while one member would recommend tightening the standards. CASAC later announces a teleconference on Feb. 11-12 to continue discussing the committee’s recommendations for ozone.

Dec. 16, 2019 CASAC finalizes its report to Administrator Wheeler on the PM NAAQS. The report confirms that CASAC is divided as to whether the current science calls into question the adequacy of the existing standards, but ultimately, CASAC recommends EPA retain the existing NAAQS.

Jan. 27, 2020 EPA publishes the final 2019 Integrated Science Assessment for PM.

Jan. 29, 2020 EPA releases the final Policy Assessment for PM. The final assessment states that ” the available scientific evidence, air quality analyses, and the risk assessment…can reasonably be viewed as calling into question the adequacy of the public health protection afforded by the combination of the current annual and 24-hour primary PM2.5 standards. In contrast to this conclusion, a conclusion that the current primary PM2.5 standards do provide adequate public health protection would place little weight on the broad body of epidemiologic evidence reporting generally positive and statistically significant health effect associations, particularly for PM2.5 air quality distributions likely to have been allowed by the current primary standards.” This conclusion calls into question CASAC’s recommendation to retain the existing PM NAAQS.

Feb. 10, 2020 The Southern District of New York holds that EPA violated the law when issuing the conflicts of interest directive and vacates the relevant language. As a result, until EPA modifies its decision or fixes the procedural defects the court identified, EPA cannot categorically prohibit grant recipients from serving on advisory panels. Natural Resources Defense Council, Inc. v. EPA, No. 1:19-cv-05174-DLC.

Feb. 12, 2020 CASAC agrees on a final report to Administrator Wheeler recommending no change to the existing ground-level ozone standard. The report also urges EPA to restore the independent ozone review panel and in-person meetings between CASAC and members of the panel.

March 4, 2020 EPA sends its proposed decision on whether to maintain the Particulate Matter NAAQS to the Office of Management and Budget for review. This is a required step prior to publishing the guidance.

April 1, 2020 Administrator Wheeler sends a letter to CASAC Chair Tony Cox stating that EPA will stick to its 2020 deadline for the Ozone NAAQS. Wheeler acknowledges that this deadline means many of CASAC’s comments on the Integrated Science Assessment that are “more substantial or cross-cutting” will not be addressed in this review cycle.

April 14, 2020 EPA announces that it is proposing to retain the PM NAAQS. The proposed action is open for comment until June 29, 2020.

May 31, 2020 EPA publishes the final Policy Assessment for ozone, affirming that the most recent scientific evidence continues to support retaining the current ozone NAAQS. The Policy Assessment projects that EPA will publish a proposed decision on retaining or changing the ozone NAAQS in mid-2020.

July 13, 2020 EPA announces it is proposing to retain the ozone NAAQS. The proposed decision will be open for comment once it’s published in the Federal Register.

Nov. 4, 2020 EPA submits its final rule to maintain the PM NAAQS to the Office of Management and Budget (OMB) for final review. This is the last step in the review process before EPA publishes the rule in the Federal Register and it becomes effective. 

Dec. 7, 2020 EPA issues a final rule refusing to update the primary and secondary NAAQS for particulate matter (PM) due to “important uncertainties” in the evidence regarding adverse health effects of PM below current standards. The rule bypasses a report published by EPA’s Office of Air Quality Planning and Standards finding that the current primary PM standards fail to prevent “a substantial number” of premature deaths each year.

Dec. 18, 2020 EPA issues a response to significant comments received on the PM NAAQS proposed rule. EPA defends its refusal to consider evidence linking soot exposure and increased COVID-19 mortality arguing that “research in this area is new and emerging.”

Dec. 31, 2020 EPA publishes a final rule retaining the current NAAQS for ozone, finding “that the current primary standard is requisite to protect public health, including the health of at-risk populations, with an adequate margin of safety, and should be retained, without revision.” The rule is effective immediately.

Jan. 13, 2021 A coalition of 17 states and New York City files a lawsuit against EPA for refusing to update the PM NAAQS. The coalition alleges that EPA conducted a flawed review of the current NAAQS and disregarded the scientific consensus on the need for stronger standards. California v. EPA, No. 21-01014 (D.C. Cir.). 

Jan. 19, 2021 A coalition of 15 states, the District of Columbia, and New York City challenges EPA’s decision not to update the ground-level ozone NAAQS. The group alleges that the decision violates EPA’s Clean Air Act obligations by conducting a flawed review process that imperils public health. New York v. EPA, [Docket No. Pending] (D.C. Cir.). 

Jan. 19, 2021 A group of 11 public health and environmental organizations challenges EPA’s decision not to update the PM NAAQS. The group argues that EPA rushed its decision to not update the NAAQS, despite the scientific consensus of the danger of the current PM standards. American Lung Association v. EPA, No. 21-01027 (D.C. Cir.).

Early Biden Actions

Jan. 20, 2021 President Biden issues an Executive Order revoking a Trump-era memo that required EPA to reevaluate its process for setting the NAAQS. Administrator Pruitt relied on the President’s memo to issue the Back-to-Basics memo that accelerated EPA’s process for reviewing and setting the NAAQS. Under the same order, EPA will review both the ozone and PM NAAQS rules.

Feb. 9, 2021 The Center for Biological Diversity (CBD) sues EPA alleging the agency failed to consider the effects of soot pollution on endangered plants and animals when it refused to update the PM NAAQS. Center for Biological Diversity v. EPA, [Docket No. Pending] (D.C. Cir.).

Feb. 11, 2021 14 public health and environmental groups challenge EPA’s refusal to update the ozone NAAQS, arguing that EPA rushed the scientific review process, and endangered public health. American Academy of Pediatrics, et al., v. EPA, [Docket No. Pending] (D.C. Cir.).

Feb. 16, 2021 A coalition of states petitions EPA to reconsider the PM NAAQS, pointing to new studies demonstrating significant long-term health risks from PM exposure, including increased mortality from COVID-19. The same day, a coalition of public health and environmental groups submits a similar petition.

Feb. 25, 2021 The Center for Biological Diversity files a petition for review in the DC Circuit challenging the ozone NAAQS, claiming EPA failed to consult wildlife experts regarding the rule’s impact on endangered species. The suit is similar to a suit CBD filed regarding the PM NAAQS. Center for Biological Diversity v. EPA, No. 21-1073 (DC Cir.).

June 10, 2021 EPA announces it will reconsider the Trump administration decision not to strengthen PM standards. It plans to issue a proposed rulemaking in Summer 2022.