09/27/2017 - Regulatory Rollback

Implementation of 2015 Ozone National Ambient Air Quality Standards

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

Ground-level ozone, or smog, is formed when pollution from vehicles, power plants, and other industrial sources reacts with sunlight. It can aggravate asthma and cause other respiratory problems, especially in children who are playing outdoors and people with existing lung problems.

Stricter ozone standards were finalized in 2015 and set to take effect October 1, 2017. These standards are called the National Ambient Air Quality Standards (NAAQS). Once the updated NAAQS are in effect, EPA must designate counties as either meeting the new standards (in attainment) or failing to meet them (non-attainment).

This page tracks EPA’s implementation of the 2015 ozone standards, EPA’s attainment designations, and challenges to those determinations.

EPA also finalized rules refusing to update the ozone NAAQS as part of the required five-year review process. For more information, see our post, National Ambient Air Quality Standards for PM and Ozone.

States that are upwind affect downwind states’ ability to meet the NAAQS. For information on cross-state air pollution and downwind states’ petitions seeking greater emissions cuts from upwind states, see our posts: Cross-state Air Pollution Rule and Section 126 Petitions.

Current Status

States and other interested parties have sued EPA for failing to make compliance determinations by the statutory deadline. For some areas for which EPA has issued attainment designations, states and environmental groups are challenging these designations.

Environmental groups have also challenged EPA’s implementing regulations for the 2015 and 2018 standards. 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.


Oct. 26, 2015 EPA issues a rule to tighten national ozone pollution standards 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


April 7, 2017 EPA asks the Court to delay the oral argument scheduled for April 19, 2017. EPA states it “intends to closely review the 2015 Rule, and the prior positions taken by the Agency with respect to the 2015 Rule may not necessarily reflect its ultimate conclusions after that review is complete.”

April 11, 2017 The Court removes the argument from its calendar and orders EPA to provide status reports every 90 days.

June 6, 2017 Administrator Pruitt announces EPA will delay implementation of the new ozone standards by one year.

June 28, 2017 EPA publishes a formal notice that it will delay implementation of the ozone standards by one year to October 1, 2018.

July 12, 2017 Environmental groups sue EPA over the delay of the ozone rule. American Lung Association et al v. EPA, Case No. 17-1172 (D.C. Cir.).

Aug. 1, 2017 Fifteen states and the District of Columbia sue EPA over the delay of the rule. New York v. EPA, No. 17-1185 (D.C. Cir.)

Aug. 2, 2017 EPA announces it will walk back the national delay and proceed as originally scheduled.

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.

July 3, 2018 The Court of Appeals for the District of Columbia returns the Murray Energy Corp. v. EPA litigation to its active docket. Murray Energy Corp. v. EPA, No. 15-1385 (D.C. Cir.).

Aug. 1, 2018 EPA files a status report with the DC Circuit indicating that “the appropriate EPA officials have reviewed the 2015 [Ozone NAAQS] Rule and have determined that at this time, EPA does not intend to revisit the 2015 Rule.” In this filing, EPA indicated it intends to address background ozone and the “relative contribution of natural and anthropogenic ozone to design values” in its new review of the Ozone NAAQS. “EPA anticipates revisiting both the question of when background concentrations interfere with attainment of the NAAQS and the question of how to consider potential interference with attainment in deciding whether or how to revise the NAAQS.” Murray Energy Corp. v. EPA, No. 15-1385 (D.C. Cir.).

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 NAAQS. Downwinders at Risk v. EPA, 19-1024 (D.C. Cir.).

Aug. 23, 2019 The DC Circuit upholds the 2015 primary ozone NAAQS in Murray Energy Corp. v. EPA, No. 15-1385. The panel denies most challenges, sends back secondary standards to the agency for reconsideration, and vacates a provision that grandfathered in permit applications submitted by industry before the 2015 revision that would not comply with the newly revised NAAQS.

Sep. 22, 2020 A three-judge panel of the DC Circuit holds oral arguments in Downwinders at Risk v. EPA, No. 19-1024.

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 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).


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.

Dec. 5, 2017 New York attorney general Eric T. Schneiderman announces 15 attorneys general sue EPA for its failure to designate non-attainment areas. Northern District of California, Case 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.

Dec. 22, 2017 EPA announces it sent letters to areas not covered by the attainment designations, seeking further information from them in order to make a designation, with a 120-day deadline for response.

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.”

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 17, 2018 EPA completes 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. The designations are posted in the Federal Register on July 25, 2018.

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.

March 25, 2019 WildEarth Guardians sue EPA for failing to determine whether the Denver area meets the 2008 ground level ozone standards of 75 parts-per-billion. WildEarth alleges that EPA was required to set the compliance status of the area by January 20, 2019. WildEarth Guardians v. Wheeler, No. 1:19-cv-00897 (D. Co.)

March 26, 2019  Colorado withdraws its request to extend the attainment date for the 2008 Ozone NAAQS for the Denver Metropolitan/North Front Range Nonattainment Area.

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.).

July 22, 2019 Judge Kane finds Administrator Wheeler failed to comply with his nondiscretionary duty to determine whether the Denver area should be downgraded to “serious nonattainment” with the 2008 Ozone NAAQs by January 20, 2019. Wheeler does not object to the finding, telling the court he has not yet made this determination. WildEarth Guardians v. Wheeler, No. 1:19-cv-00897 (D. Co.).

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.).


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.).

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

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.