EPA On Track to Regulate Fine Particulates More Stringently: D.C. Circuit Affirms Revised PM 2.5 NAAQS

EPA's judicial winning streak continues. Today, the D.C. Circuit Court of Appeals affirmed EPA's regulations lowering the PM 2.5 National Ambient Air Quality Standard from 15.0 ug/m3 to 12.0 ug/m3. This was not a close case or a difficult decision. Indeed, as we had previously pointed out, the D.C. Circuit had previously rejected EPA's decision to keep the NAAQS at 15 ug/m3 and EPA's Clean Air Science Advisory Committee had supported lowering the NAAQS to 12 ug/m3 or 13ug/m3. Given the courts' deference in recent years to EPA technical decisions supported by CASAC, this outcome was not a surprise.

As per usual, the Court noted that it "exercise[s] great deference when we evaluate claims about competing bodies of scientific research." In light of that deference, the Court's conclusion was "brief":