Non-GHG Emission Standards with GHG Co-Benefits

Ambient Standards (NAAQS)

This section covers ambient standards promulgated under the National Ambient Air Quality Standards (NAAQS) Clean Air Act program.

NAAQS for Ozone

Under section 109 of the Clean Air Act, EPA is required to set National Ambient Air Quality Standards (NAAQS) for air pollutants for which it has made an endangerment finding under section 108. Section 109 directs EPA to issue “primary” and “secondary” NAAQS. Primary NAAQS must be set at a level “requisite to protect the public health” with “an adequate margin of safety.” Secondary NAAQS must be set at a level “requisite to protect the public welfare.”

On June 5, 2023, EPA published a final rule with Federal Implementation Plan (FIP) requirements for twenty-six states regarding nonattainment of the 2015 ozone National Ambient Air Quality Standard (NAAQS). 88 Fed. Reg. 36,654 (June 5, 2023). The rule was proposed with EPA’s authority under the “good neighbor” provision of the Clean Air Act. (See Utah v. EPA in “Litigation” below.)

After the final rule was stayed by the Supreme Court (see details below), EPA issued a final interim rule in response to the judicial stay on November 6, 2024. 89 Fed. Reg. 87,960 (Nov. 6, 2024).

Litigation

Challenge to 2023 Rule - Utah v. EPA

On June 20, 2023, Utah and other parties filed a petition for review of EPA’s final rule in the D.C. Circuit Court of Appeals. The plaintiffs also filed a motion to stay the rule in the case, Utah v. EPA (No. 23-01157), which the Court of Appeals denied. Plaintiffs then filed emergency applications to the Supreme Court for a stay of the rule in the following cases: Ohio v. EPA (No. 23A349), Kinder Morgan v. EPA (No. 23A350), American Forest & Paper Association v. EPA (No. 23A351), United States Steel Corporation v. EPA (No. 23A384). The Supreme Court granted the applications and stayed the rule.

Biden Administration (2021-2024)

On June 5, 2023, EPA published a final rule with Federal Implementation Plan (FIP) requirements for twenty-six states regarding nonattainment of the 2015 ozone National Ambient Air Quality Standard (NAAQS). 88 Fed. Reg. 36,654 (June 5, 2023). The rule was proposed with EPA’s authority under the “good neighbor” provision of the Clean Air Act. (See Utah v. EPA in “Litigation” below.)

After the final rule was stayed by the Supreme Court (see details below), EPA issued a final interim rule in response to the judicial stay on November 6, 2024. 89 Fed. Reg. 87,960 (Nov. 6, 2024).

First Trump Administration (2017-2020)

Following a review of the Ozone NAAQS, in December 2020 the EPA decided not to update the 2015 standards, described below.

Obama Administration (2009–2016)

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.

Litigation

Challenge to 2023 Rule - Utah v. EPA

On June 20, 2023, Utah and other parties filed a petition for review of EPA’s final rule in the D.C. Circuit Court of Appeals. The plaintiffs also filed a motion to stay the rule in the case, Utah v. EPA (No. 23-01157), which the Court of Appeals denied. Plaintiffs then filed emergency applications to the Supreme Court for a stay of the rule in the following cases: Ohio v. EPA (No. 23A349), Kinder Morgan v. EPA (No. 23A350), American Forest & Paper Association v. EPA (No. 23A351), United States Steel Corporation v. EPA (No. 23A384). The Supreme Court granted the applications and stayed the rule.

NAAQS for Particulate Matter

Under section 109 of the Clean Air Act, EPA is required to set National Ambient Air Quality Standards (NAAQS) for air pollutants for which it has made an endangerment finding under section 108. Section 109 directs EPA to issue “primary” and “secondary” NAAQS. Primary NAAQS must be set at a level “requisite to protect the public health” with “an adequate margin of safety.” Secondary NAAQS must be set at a level “requisite to protect the public welfare.”

On January 27, 2023, EPA published a proposed rule to reconsider the National Ambient Air Quality Standards (NAAQS) for particulate matter. 88 Fed. Reg. 5,558 (Jan. 27, 2023). The proposal discusses the causal link between particulate matter and climate effects. On March 6, 2024, EPA finalized the rule. 89 Fed. Reg. 16,202 (Mar. 6, 2024). (See Kentucky v. EPA in “Litigation” below.)

Litigation

Challenge to 2024 NAAQS - Kentucky v. EPA

In March 2024, states and private parties filed a petition for review of EPA’s final rule in the D.C. Circuit Court of Appeals. The consolidated case has been briefed and oral argument was held on December 16, 2024.

Biden Administration (2021-2024)

On January 27, 2023, EPA published a proposed rule to reconsider the National Ambient Air Quality Standards (NAAQS) for particulate matter. 88 Fed. Reg. 5,558 (Jan. 27, 2023). The proposal discusses the causal link between particulate matter and climate effects. On March 6, 2024, EPA finalized the rule. 89 Fed. Reg. 16,202 (Mar. 6, 2024). (See Kentucky v. EPA in “Litigation” below.)

Litigation

Challenge to 2024 NAAQS - Kentucky v. EPA

In March 2024, states and private parties filed a petition for review of EPA’s final rule in the D.C. Circuit Court of Appeals. The consolidated case has been briefed and oral argument was held on December 16, 2024.