## Facts

- EPA revised the ozone National Ambient Air Quality Standard (NAAQS) from a one-hour standard (0.12 ppm) to a more stringent eight-hour standard (0.08 ppm).
- In a 2004 implementation rule for the eight-hour ozone NAAQS, EPA revoked the one-hour standard on a set date and adopted transition rules for nonattainment areas.
- EPA concluded that certain one-hour-era control obligations would not be retained under the eight-hour regime, including some Subpart 2 programs such as specified new source review (NSR) requirements and penalty provisions.
- EPA also interpreted the Clean Air Act (CAA) to allow some eight-hour ozone nonattainment areas to be regulated primarily under Subpart 1 (general nonattainment provisions) rather than Subpart 2 (ozone-specific scheme).
- Environmental organizations, South Coast Air Quality Management District, states, and industry groups petitioned for review.
- In an earlier decision, the court vacated and remanded significant portions of the rule for misreading the CAA’s Subpart 1/Subpart 2 structure and for violating anti-backsliding requirements.
- Multiple parties sought panel rehearing and rehearing en banc, disputing the statutory analysis and the scope of vacatur.

## Issues

1. Whether EPA could treat Subpart 1 as displacing or substantially supplanting Subpart 2 when implementing the revised eight-hour ozone NAAQS.
2. Whether the CAA required retention of certain one-hour ozone controls (including specified NSR and penalty provisions) when transitioning to the eight-hour standard under anti-backsliding principles.
3. Whether the court’s earlier vacatur remedy was overbroad and should be modified to preserve unaffected portions of the implementation rule.

## Decision

- The court denied all petitions for panel rehearing and rehearing en banc.
- The court reaffirmed that EPA exceeded its statutory authority by interpreting the CAA to allow Subpart 1 to function as a substitute for Subpart 2’s ozone-specific requirements in implementing the eight-hour standard.
- The court reaffirmed that EPA’s selective retention of one-hour-era requirements failed to satisfy anti-backsliding obligations because it allowed elimination of required controls without replacement by measures at least as stringent.
- The court clarified that its remedy operated as a partial vacatur, permitting continued implementation of lawful portions of the eight-hour ozone program while EPA revised the invalidated elements.

## Legal Principles

- When Congress prescribes pollutant-specific implementation requirements, an agency may not use general statutory provisions to nullify or bypass the more specific scheme.
- EPA’s gap-filling authority in implementing a revised NAAQS must be exercised consistently with the CAA’s structure and cannot rewrite the boundary between Subpart 1 and Subpart 2 for ozone.
- Anti-backsliding in the CAA requires that, during transition to a revised (more stringent) NAAQS, existing control obligations cannot be discarded unless replaced with measures at least as stringent.
- Vacatur of unlawful regulatory provisions may be tailored to avoid disruptive regulatory gaps; partial vacatur may preserve valid program components while the agency cures statutory defects on remand.

## Conclusion

The D.C. Circuit refused to revisit its prior invalidation of key portions of EPA’s eight-hour ozone implementation rule, holding that EPA could not shift ozone implementation from Subpart 2 to Subpart 1 and could not drop one-hour-era controls in violation of anti-backsliding requirements, while clarifying that the remedy preserved unaffected parts of the program pending revision on remand.


S. Coast Air Quality Mgmt. Dist. v. EPA, 489 F.3d 1245 (D.C. Cir. 2007)