## Facts

- The Clean Air Act requires EPA to set and periodically review primary National Ambient Air Quality Standards (NAAQS) at a level requisite to protect public health with an adequate margin of safety, including for sensitive populations.
- EPA historically regulated sulfur dioxide (SO₂) through 24-hour and annual primary standards but concluded those metrics did not adequately address short-term exposure spikes affecting vulnerable groups such as asthmatics.
- EPA relied heavily on controlled human exposure studies of exercising asthmatics indicating bronchoconstriction and symptoms from short-burst SO₂ exposures in the 200–300 ppb range in some subjects, with statistically significant effects at higher levels (about 400 ppb and above).
- EPA promulgated a new primary 1-hour SO₂ NAAQS of 75 ppb, expressed as a 3-year average of the 99th percentile of the daily maximum 1-hour concentrations.
- A coalition of industry and state petitioners challenged the final rule and EPA’s subsequent denial of petitions for reconsideration; environmental and public-health organizations intervened in support of EPA.

## Issues

1. Whether EPA violated APA/Clean Air Act notice-and-comment requirements by finalizing a “hybrid” 1-hour SO₂ standard (including its statistical form and indicator) that was not adequately disclosed in the proposal.
2. Whether EPA acted arbitrarily or capriciously, or exceeded its statutory authority, by selecting a 75-ppb 1-hour SO₂ standard in light of evidence that statistically significant adverse effects were observed at higher exposure levels.

## Decision

- The court denied the consolidated petitions for review and upheld the 75-ppb 1-hour primary SO₂ NAAQS and EPA’s denial of reconsideration.
- The final rule satisfied notice-and-comment because it was a logical outgrowth of the proposal and accompanying materials.
- EPA’s choice of level and form was reasonable under the Clean Air Act’s public-health and margin-of-safety mandate and was supported by the administrative record.

## Legal Principles

- A final agency rule satisfies notice-and-comment when it is a logical outgrowth of the proposed rule such that interested parties should have anticipated the possibility of the final approach.
- Under Clean Air Act § 109, EPA may set primary NAAQS to protect sensitive populations with an adequate margin of safety, which permits protective judgment in the face of scientific uncertainty and individual variability.
- Arbitrary-and-capricious review is deferential to EPA’s technical judgments when the agency explains a rational connection between the evidence (including risk/exposure assessments and clinical studies) and the selected level and statistical form.
- The Clean Air Act does not require EPA to set a standard no lower than the lowest concentration at which statistically significant adverse effects were observed; EPA may adopt a more protective standard if reasonably justified.

## Conclusion

The D.C. Circuit held that EPA provided adequate notice of the range of regulatory approaches under consideration and reasonably exercised its statutory discretion to adopt a 75-ppb 1-hour SO₂ NAAQS to protect asthmatics and other sensitive groups from short-term exposure spikes with an adequate margin of safety.


Nat'l Envtl. Dev. Ass'n's Clean Air Project v. EPA, 686 F.3d 803 (D.C. Cir. 2012)