Summary of Court Decision Regarding Stringency of 2015 Ozone Standard

In 2015, EPA lowered the primary and secondary ozone national ambient air quality standards (NAAQS) from 75 parts per billion (ppb) to 70 ppb. The final rule also included a grandfathering provision for the Prevention of Significant Deterioration (PSD) permitting program to allow compliance with the revised ozone standards not to delay the processing of certain pending permit applications.

Industry and state petitioners challenged the 2015 ozone NAAQS as overly stringent, and environmental NGOs and public health groups challenged the standard as not sufficiently stringent. Environmental petitioners had also argued that the grandfathering provision was inconsistent with the CAA.

On August 23, 2019, the D.C. Circuit upheld EPA's primary and secondary 2015 ozone NAAQS. However, the Court remanded certain aspects of the secondary ozone standard for EPA's reconsideration and vacated the final rule's grandfathering provision. This MJB&A Issue Brief summarizes the key aspects of the Court's opinion.