As we have noted previously (An Opportunity for a New Federal-State Relationship Under the Regional Haze Program, July 17, 2017; A New Perspective on Regional Haze Regulation?, February 14, 2017), the US Environmental Protection Agency (EPA) recently signaled a new openness to recognizing state prerogatives and flexibility in implementing the regional haze program under the Clean Air Act (CAA). That program addresses impairment of visibility in the skies over protected national parks and wilderness areas that is attributed to widespread haze resulting from emissions to the air from varied sources.