A federal appeals court denied a complaint by California's South Coast Air Quality Management District targeting the U.S. Environmental Protection Agency requirements for the 2008 National Ambient Air Quality Standards for ozone. But the court partially upheld a related challenge brought by environmental groups involving the revocation of the previous ozone standard.

South Coast had asked the U.S. Court of Appeals for the District of Columbia Circuit to invalidate the 2008 National Ambient Air Quality Standards, or NAAQS, provisions addressing what sources can be counted towards emissions reductions goals. According to the EPA, states may not take credit for reductions of ozone-forming pollutants that occur from sources outside of a nonattainment area to meet the rule's progress goals. "There is no legal basis for allowing states to credit reductions achieved at sources outside the nonattainment area," the EPA explained in the final rule.

But South Coast argued that because downwind nonattainment areas are impacted by emissions from upwind areas, the EPA could reasonably interpret "in the area" to mean a region encompassing a larger area of possible emission sources.

The D.C. Circuit on Feb. 16 rejected South Coast's complaint. Finding the text unambiguous, the court ruled that "in the area" refers to baseline emissions within the nonattainment area.

However, the court granted in part a separate complaint consolidated with the South Coast matter filed by the Sierra Club, Conservation Law Foundation, Downwinders at Risk, and Physicians for Social Responsibility.

The groups alleged that the EPA "acted arbitrarily and capriciously" in the way it replaced the 1997 NAAQS with the 2008 version. The complex challenge essentially asked the court to review whether the EPA, when promulgating the 2008 NAAQS, improperly waived the obligation for states to meet the 1997 version of the rule. The EPA contended that the Clean Air Act allows the agency to revoke a previous NAAQS when updating a rule if it establishes adequate anti-backsliding measures.

The court acknowledged finding previously that the EPA may revoke a previous NAAQS when updating a rule. However, it determined that the EPA failed to establish adequate backsliding provisions when it vacated the 1997 standard and replaced with the 2008 standards. The D.C. Circuit therefore vacated several provisions of the rule related to the backsliding issue.

Judge David Sentelle penned the court's decision for a panel that also included Judges Merrick Garland and Judith Rogers. South Coast v. U.S. EPA (No. 15-1115)