Regulatory Tracker

Implementation of 2015 Ozone National Ambient Air Quality Standards (NAAQS)

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On this page we track EPA’s implementation of the 2015 ozone standards, EPA’s attainment designations, and challenges to those determinations. For information on EPA’s National Ambient Air Quality Standards (NAAQS) scientific review and approval process read our NAAQS Regulatory Tracker page here. To follow EPA’s work on the Ozone NAAQS, see our Ozone NAAQS Regulatory Tracker page here and for information on the particulate matter (PM) NAAQS, see our PM NAAQS Regulatory Tracker page here. Click here for our Air Transport – Cross-State Air Pollution Rule / Good Neighbor Rule, Section 126 Petitions, and Section 184 Ozone Transportation Commission Petition page.

Quick Take

EPA under the Trump administration delayed implementation of the 2015 ozone National Ambient Air Quality Standards (NAAQS) and also designated high emission areas as in attainment with the standards. Under legal pressure from environmental groups due to these missed statutory deadlines and baseless attainment findings, EPA under the Biden administration is working to implement the 2015 ozone NAAQS by making compliance determinations and is also facing legal challenges to those attainment and nonattainment designations. 

Why it Matters

Section 109 of the Clean Air Act (CAA) requires EPA to review existing NAAQS and make appropriate revisions every five years to provide requisite protection of public health and welfare. The Obama Administration finalized more stringent CAA NAAQS for ozone in 2015, which were set to take effect October 1, 2017. This action triggered EPA’s obligation to designate attainment areas as either meeting the new standards (in attainment) or failing to meet them (non-attainment). Section 110 of the CAA requires states to develop state implementation plans (SIPs) that provide for the attainment and maintenance of such standards and submit them to EPA for approval.

Current Status

Environmental groups challenged EPA’s implementing regulations for the 2015 standard. The DC Circuit struck down three provisions in these rules, finding EPA’s interpretation of these elements were inconsistent with the CAA’s plain language or unreasonable.

States and other interested parties have sued EPA for failing to make compliance determinations by the statutory deadlines. For some areas for which EPA has issued attainment designations, states and environmental groups are challenging these designations. On May 24, 2021, the Biden EPA issued a final rule reversing designations in seven states in response to the DC Circuit’s July 10, 2020 ruling on such designations. EPA has also recently entered into several consent decrees to act on and publish certain SIPs by specific dates.

Obama administration
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Oct. 26, 2015 EPA issues a rule to tighten national ozone pollution standards to 70 parts per billion (ppb) based on the latest science. The new standards are set to take effect October 1, 2017.

Sep. 14, 2016 Murray Energy sues EPA challenging the new standards. Murray Energy Corp. v. EPA, Case No. 15-1385 (D.C. Cir.).

Nov. 17, 2016 EPA proposes nonattainment classification thresholds and compliance timelines for the 2015 rule.

Trump Era – Implementation Regulations for the 2015 Ozone NAAQS
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July 3, 2018 EPA sends the final draft of its implementation regulations for 2015 ground-level ozone standard to the White House Office of Management and Budget for review.

Dec. 6, 2018 EPA publishes a rule finalizing implementation requirements for the 2015 NAAQS. The final rule is effective on February 4, 2019.

Feb. 4, 2019 Environmental groups ask the DC Circuit to review EPA’s final implementation rule for the 2015 NAAQSDownwinders at Risk v. EPA, 19-1024 (D.C. Cir.).

Sep. 23, 2019 EPA approves Texas’ State Implementation Plan.

Jan. 29, 2021 A three-judge panel for the U.S. Court of Appeals for the DC Circuit strikes down three parts of EPA’s 2015 and 2018 rules for implementing the 2015 ozone NAAQS. Specifically, the court strikes down the interprecursor trading program, which allowed emitters to use permitting offsets to comply with the NAAQs, and EPA’s interpretation of the CAA’s contingency measures requirements because both “contravene the statute’s unambiguous language.” The court also vacates EPA’s implementation of the milestone compliance demonstration requirements, which allowed states to demonstrate compliance showing “percentage implementation” instead of actual emissions reductions, because “it rests on an unreasonable interpretation of the statute.” Sierra Club v. EPA, No. 15-1465 (DC Cir.) (consolidated with Downwinders at Risk v. EPA, No. 19-1024).

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Oct. 1, 2017 Deadline for EPA to make all compliance determinations.

Nov. 16, 2017 EPA certifies some 2,650 areas as in compliance (or in attainment) of the rule. It does not designate any non-attainment areas or release a timeline for doing so, which is necessary to “start the clock for states to come up with cleanup plans.

Dec. 4, 2017 A coalition of public health and environmental groups sue EPA for its delay of designating non-attainment areas. American Lung Assoc., et al. v. EPA, No. 3:17-cv-06900 (N.D.Cal.).

Dec. 5, 2017 New York attorney general Eric T. Schneiderman announces fifteen attorneys general sue EPA for its failure to designate non-attainment areas. State of California, et al v. EPA, No. 3:17-cv-06936 (N.D.Cal.).

Dec. 19, 2017 The DC Circuit Court orders EPA to “file a status report identifying with precision and specificity when it plans to file a final rule establishing air quality designations” by January 12, 2018, for the areas that were not covered by the attainment designations made on November 16, 2017. American Lung Assoc., et al v. EPA, No. 17-01172 (D.C. Cir.).

Jan. 5, 2018 EPA publishes notice that it will make the remaining attainment designations by April 30, 2018.

Jan. 19, 2018 EPA files declarations with both the Northern District of California and DC Circuit stating it will make all remaining attainment designations by April 30, 2018, with the exception of eight counties in the San Antonio, TX area, which it will designate by August 10, 2018.

Feb. 7, 2018 A three-judge panel of the DC Circuit Court orders EPA to file a progress report by May 15, 2018 “detailing the status of all final designations for the 2015 ozone national ambient air quality standards.” American Lung Assoc., et al v. EPA, No. 17-01172 (D.C. Cir.).

March 1, 2018 EPA issues a final rule setting the compliance timelines for areas in nonattainment and “establishing the air quality thresholds that define the classifications assigned to all nonattainment areas,” which were proposed in 2016 by the Obama EPA. The rule will take effect on May 8, 2018.

March 12, 2018 A Northern District of California District Court rules that EPA cannot delay the Texas counties, or any others, and must make all designations by July 17, 2018.

March 30, 2018 EPA publishes notice that it will finish designations for the Texas counties by the court-ordered deadline, and lists an intended designation for each area. The notice is open for public comment until April 30, 2018.

April 30, 2018 EPA announces it had made all remaining designations with the exception of the eight Texas counties. Fifty-one areas are in nonattainment, starting a clock for them to make improvements.

May 22, 2018 Fifteen states and the District of Columbia file a complaint with the US Circuit Court of Appeals for the DC Circuit, saying EPA had not listed its new ozone designations in the Federal Register. This listing is required to start the 60-day compliance clock. On May 24, 2018 a coalition of public health and environmental groups file in agreement with the states.

June 4, 2018 EPA publishes in the Federal Register designations for “all remaining areas, except for eight counties in the San Antonio, Texas metropolitan area,” starting a 60-day compliance clock for the designated areas.

July 25, 2018 EPA posts designations for the eight remaining counties in Texas that had not yet been designated. EPA designates Bexar County (where San Antonio, Texas is located) as a nonattainment area and the remaining seven counties as attainment/unclassifiable areas.

Jan. 2, 2019 the DC Circuit dismisses as moot American Lung Association v. EPA, No. 17-1172, regarding EPA’s delay in promulgating air quality designations.

May 7, 2019 Sierra Club and Center for Biological Diversity sue EPA to force the agency to determine the Ozone NAAQs compliance status of Dallas-Fort Worth, Baltimore, Houston, Chicago, New York City, and seven other metropolitan areas. The groups allege that EPA has missed its January 20, 2019 deadline to determine whether these areas are in violation of the Ozone standards. This suit is similar to the March 25, 2019 WildEarth Guardians lawsuit. Center for Biological Diversity v. EPA, No. 3:19-cv-02462 (N.D. Cal.).

Dec. 11, 2019 The district court in Center for Biological Diversity v. EPA orders that EPA must finalize a determination for Imperial County, California by Feb. 13, 2020. EPA has issued determinations for the other counties at issue in the case. No. 3:19-cv-02462 (N.D. Cal.).

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Aug. 1, 2018 Clean Wisconsin files a suit challenging the attainment designations of counties in Wisconsin. Clean Wisconsin v. EPA, No. 18-1203 (D.C. Cir.).

Aug. 2, 2018 Illinois Attorney General Madigan and the City of Chicago files suit challenging attainment designations made for counties in Indiana, Illinois, and Wisconsin. Illinois v. EPA, No. 18-1208 (D.C. Cir.). Three lawsuits challenging designations have also been filed by environmental groups Sierra Club, Environmental Law & Policy Center, Respiratory Health Association, and the city of Sunland Park, NM, and Familias Unidas del Chamizal, an El Paso, TX.

Aug. 28, 2018 Texas Attorney General Paxton files suit challenging attainment designations made for Bexar County including the San Antonio area. Texas v. EPA, No. 18-60606 (5th Cir.).

July 10, 2020 The DC Circuit orders EPA to reconsider its 2015 ozone compliance designations in more than a dozen counties in Colorado, Illinois, Indiana, Michigan, Missouri, Texas, and Wisconsin. Clean Wisconsin v. EPA, No. 18-1203.

biden administration
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May 24, 2021 EPA issues a final rule revising or reversing Trump-era designations for the 2015 ground-level ozone NAAQS in seven states. The rule is in response to a D.C. Circuit ruling sending the designations back to EPA. Clean Wisconsin v. EPA, No. 18-1203 (D.C. Cir.).

May 26, 2021 Environmental groups file an amended deadline suit against EPA for failing to issue “formal findings of failure” to New York, Pennsylvania, and Virginia, which have all exceeded the Clean Air Act’s six-month deadline to submit revised SIPs in compliance with the 2008 and 2015 ozone NAAQS. Center for Biological Diversity et al. v. Regan, No. 4:21-cv-02498 (N.D. Cal.).

July 23, 2021 EPA and environmental groups enter into a consent decree, which requires EPA, by specific dates, to approve or disapprove, in whole or in part, SIPs for Coachella Valley and Kern County, California as well as the Metro Denver area.  Center for Biological Diversity et al v. Regan, Docket No. 3:20-cv-06020 (N.D. Cal.)

July 29, 2021 EPA published a notice of a proposed consent decree in State of New York, et al. v. Regan et al., No. 21 Civ. 252 (ALC) (S.D.N.Y.) with New York, Connecticut, Delaware, Massachusetts, and New Jersey, and the City of New York which would establish deadlines for EPA to act under the good neighbor provision of the Act to either approve or disapprove portions of six 2015 ozone NAAQS SIPs by Indiana, Kentucky, Michigan, Ohio, Texas, and West Virginia.  Comments on the proposed consent decree are due by August 30, 2021.

Oct. 15, 2021 EPA releases a proposed consent decree in Downwinders at Risk v. Regan, which will require EPA to approve or disapprove six states’ 2015 ozone SIPs by April 30, 2022 or propose a FIP addressing the good neighbor obligations for such states by February 22, 2022, and a final FIP by December 15, 2022. For more on this case and the Clean Air Act’s Good Neighbor Provision, see EELP’s Tracker page on the Cross-State Air Pollution Rule (CSAPR).

Oct. 22, 2021 EPA releases a proposed consent decree resolving a complaint by Our Children’s Earth Foundation requiring EPA to publish online comprehensive SIP information for almost all US states excluding California, Connecticut, North Carolina, Wisconsin, Puerto Rico and the US Virgin Islands by Dec. 21, 2021, and all US states by Sep. 30, 2022. Public comments are due by Nov. 22, 2021. Our Children’s Earth Foundation v. Regan, No. 4:20-cv-08530 (N.D. Cal.).

Nov. 18, 2021 EPA defends a Trump-era decision to allow Houston and Dallas to drop “anti-backsliding” measures required to maintain air quality under the now-revoked ozone standards set in 1979 and 1997, which have since been replaced by the 2008 and 2015 standards. EPA’s decision is based on criteria set by the D.C. Circuit in South Coast Air Quality Management District v. EPA to determine if a city will meet limits in effect. Sierra Club, et al. v. EPA, No. 20-1121 (D.C. Cir.).

Nov. 24, 2021 EPA and environmental groups reach a settlement in which the agency will issue a finding that New York and Pennsylvania failed to submit state plans implementing the 2015 ozone NAAQS by December 10, 2021. The agreement also states that EPA will approve, partially approve, or disapprove California’s standards for crude oil and natural gas facilities by July 2022. According to plaintiff environmental groups, oil and natural gas is the largest source of VOCs, which contribute to ozone pollution. Ctr. for Biological Diversity v. Regan, No. 4:21-cv-02498 (N.D. Cal.).

Nov. 30, 2021 EPA issues a final rule declaring all of Weld County in northern Colorado out of compliance with the 2015 ozone NAAQS. The county includes the majority of Colorado’s oil and gas production.

Jan. 28, 2022 The Texas Attorney General and the Texas Commission on Environmental Quality challenge EPA’s designation of El Paso County as an ozone nonattainment area. State of Texas, et al. v. EPA, et al., No. 22-01013 (D.C. Cir.).

Apr. 13, 2022 EPA proposes three actions related to 31 areas classified as “marginal” nonattainment for the 2015 ozone standard. EPA proposes to recognize six areas as achieving attainment, grant a one-year extension for attainment for the Uinta Basin, Utah area, and reclassify 24 areas that failed to achieve attainment as “moderate.” The reclassified states will then be required to submit SIP revisions to EPA by Jan. 1, 2023. A virtual public hearing will be held on May 9, 2022, and comments are due on or before June 13, 2022

May 9, 2022 D.C. Circuit Court of Appeals hears oral argument in Sierra Club, et al. v. EPA, as to whether EPA’s determination regarding the Houston and Dallas “anti-backsliding” measures is properly before the D.C. Circuit because the policy decisions amount to a national policy on backsliding. Sierra Club, et al. v. EPA, No. 20-1121 (D.C. Cir.).

June 7, 2022 Coalition of environmentalists and medical professionals file a complaint with the U.S. District Court for the District of Columbia, alleging EPA missed its deadline to make final determinations as to whether 36 “marginal” attainment areas met the 2015 ozone NAAQS, some of which are included in EPA’s April 13th proposal. Alliance of Nurses for Healthy Environments, et al. v. Regan, Docket No. 1:22-cv-01606 (D.D.C. Jun. 7, 2022).

July 12, 2022 Center for Biological Diversity filed suit in the 10th Circuit, challenging EPA’s approval of Colorado’s implementation plan for the 2015 8-Hour Ozone Standard. Center for Biological Diversity v. EPA, Docket No. 22-09546 (10th Cir. Jul. 12, 2022).

Aug. 26, 2022 The DC Circuit held that the anti-backsliding case is not reviewable by the DC Circuit because it is within EPA’s discretion to decide whether its determinations are locally applicable or nationwide in effect. The Court did not reach the merits of the case. This ruling transfers the petition to the Fifth Circuit Court of Appeals to consider EPA’s backsliding measures. Sierra Club, et al. v. EPA, No. 20-1121 (D.C. Cir.).

Oct. 7, 2022 EPA issues compliance determinations for 28 areas classified as “marginal” for the 2015 ozone NAAQS. The EPA determined that five marginal areas attained the standard by August 3, 2021, the applicable attainment date. The 22 areas that failed to attain the standards will be reclassified as “moderate” nonattainment zones on November 7, 2022. As such, the responsible state agencies must submit SIP revisions and implement controls to satisfy the requirements for “moderate” areas. EPA also granted a one-year attainment date extension for the Uinta Basin, UT.

Oct. 14, 2022 EPA proposes to approve California’s revised SIP, which incorporates a 2018 California clean bus rule that is key to reaching attainment with the 2015 Ozone NAAQS. EPA is facing pressure from environmental justice groups to approve this SIP revision to ensure enforceability rule, which may be relaxed due CARB’s financial strain. Comment here by November 14, 2022.

Sept. 29, 2023 Sierra Club sued EPA in the DC Circuit, alleging that EPA has missed its deadline to issue findings of “failure to submit” SIPs under the 2015 Ozone NAAQS for 13 states. Sierra Club v. EPA, No. 23-cv-02901 (DC Cir. Sept. 29, 2023).

Oct. 18, 2023 EPA issues a final action finding that 11 states failed to submit SIP revisions required by the CAA in a timely manner for certain nonattainment areas classified as Moderate. This finding triggers an 18-month timeline from the effective date before imposing mandatory sanctions if a State does not submit a complete SIP addressing the outstanding requirements.

Dec. 21, 2023 Sierra Club and EPA filed a joint stipulation of voluntary dismissal with prejudice, noting that EPA has taken all of the actions that they requested in the suit. Sierra Club v. EPA, No. 23-cv-02901 (DC Cir. Sept. 29, 2023).

Jan. 2, 2024 The District Court for the District of Columbia dismissed the Sierra Club case based on the joint stipulation of voluntary dismissal. Sierra Club v. EPA, No. 23-cv-02901 (DC Cir. Sept. 29, 2023).