As the EPA nears release of its proposal to revise the National Ambient Air Quality Standards (NAAQS) for ozone, the U.S. Court of Appeals for the D.C. Circuit reissued a relevant opinion that considered the validity of the approach the Agency took in setting the 2008 ozone NAAQS.  In light of the upcoming regulatory action, we review the import of the D.C. Circuit’s earlier opinion. 

In July 2013, the D.C. Circuit ruled in Mississippi v. EPA on challenges from both the left and right to the Agency’s 2008 revisions of the primary and secondary ozone NAAQS.  The thrust of those challenges was that the Agency had not based its revisions on specific scientific findings.  Environmental groups and some states also argued that the final standards did not align with recommendations made by the Clean Air Scientific Advisory Committee (CASAC). 

Declining to delve into the details of the scientific evidence presented by the various litigants, the D.C. Circuit instead said that the Agency offered a reasonable explanation for selecting the final primary standard, an approach that satisfied the procedural requirements of the Clean Air Act (CAA).  Therefore, all challenges to the primary standard were denied.  However, the D.C. Circuit was not satisfied with how the EPA set the secondary ozone standard.  Accordingly, the court ordered the Agency to reconsider the secondary standard; the court declined to vacate the standard to ensure that the protections it did provide would not be sacrificed. 

CASAC recommendation

The 2008 action lowered the primary ozone NAAQS from 0.080 parts per million (ppm) to 0.075 ppm averaged over 8  hours.  The primary standard is intended to protect human health with an adequate margin of safety.  The CAA also requires that the Agency set a secondary NAAQS to protect “human welfare,” a term that covers environmental impacts.  The EPA set the secondary standard to be identical to the primary standard.  The standards did not meet the recommendations of the CASAC, which had stated that the primary NAAQS should be in the range of 0.060 ppm to 0.070 ppm.  The CASAC also recommended that the secondary standard take a seasonal rather than an 8-hour form. 

EPA’s reasonable explanation

The court reached several key conclusions:

• Industry and a group of states (collectively “Mississippi”) argued that the EPA could not impose new ozone NAAQS because the Agency did not conduct an item-by-item analysis of why the preexisting (1997) ozone NAAQS were no longer adequate.  The D.C. Circuit disagreed.  “The statutory framework requires us to ask only whether EPA’s proposed NAAQS is ‘requisite’; we need not ask why the prior NAAQS once was ‘requisite’ but is no longer up to the task,” stated the court.  “Following Mississippi’s approach would bind EPA to potential deficiencies in past reviews because discrepancies between past and current judgments as easily reflect problems in the past as in the present.  We decline Mississippi’s invitation to enter that funhouse and will defer as long as EPA reasonably explains its actions.”
• Other states and environmental groups argued that the EPA was compelled to accept CASAC’s recommendations.  But the D.C. Circuit emphasized that the CAA requires that the EPA consider CASAC’s recommendations and, if those recommendations are not adopted, explain why.  In the rulemaking, the Agency agreed with the CASAC in that the 0.080 ppm primary standard is not sufficiently protective of public health.  But the CASAC did not indicate an exact lower value that is.  “CASAC never made clear the precise basis for its recommendation,” stated the court.  “All we know for certain is this: both CASAC and EPA believed the existence of adverse health effects to be certain at the 0.080 ppm level and reached differing conclusions about what level below 0.080 ppm was requisite to protect the public health with an adequate margin of safety.”
• The EPA justified setting the secondary standard at a level and form identical to the primary standard basically by engaging in a comparison exercise that purported to show that the primary standard was sufficient to protect public welfare.  The court rejected this approach.  “As we explained there [the 2009 decision in American Farm Bureau v. EPA, concerning the particulate matter NAAQS], it is insufficient for EPA merely to compare the level of protection afforded by the primary standard to possible secondary standards and find the two roughly equivalent.  EPA must expressly ‘determine what level of . . . protection is requisite to protect the public welfare.’”

In setting the revised ozone NAAQS, the degree to which the EPA interprets these and related conclusions reached by the D.C. Circuit will influence the capacity of the standards to withstand likely judicial challenges.

Reissued opinion in Mississippi v. EPA