During much of the Obama administration, states and EPA were in conflict about how to craft Clean Air Act plans to reduce “regional haze” impairment of visibility in national parks and wilderness areas. The technical and policy issues are daunting. Regional haze forms in the atmosphere from many sources’ air emissions — emissions from cars and trucks, construction equipment, factories and power plants (among others), plus natural sources like wildfires and dust storms. Developing regional haze implementation plans entails complex policy choices and weighing sometimes heavy compliance costs for emission controls — costs that may total in the hundreds of millions or even billions of dollars — against improvements in visibility that can be hard to measure and in some cases are even imperceptible to the human eye.

The Clean Air Act principle of “cooperative federalism” is supposed to govern: states have the main decision-making role, while EPA approves (or disapproves) state plans, depending on whether they meet statutory criteria. The Obama EPA disapproved many states’ regional haze plans and imposed stricter requirements by establishing federal plans to control sources in those states. One result was hard-fought litigation brought by states that argued that EPA’s actions exceeded federal authority. Now, with President Trump’s election, the tide of federal assertiveness in this regulatory arena may start to recede.

President Trump’s nominee as EPA administrator, Scott Pruitt, was one of several state attorneys general who battled EPA in federal court litigation over state-plan disapprovals during the Obama administration. In 2011, EPA disapproved major parts of Oklahoma’s regional haze plan — including the plan’s “best available retrofit technology,” or “BART,” controls for certain electricity-generating power plants. EPA’s 2011 action substituted a federal plan with more stringent and expensive controls. The state of Oklahoma, represented by Attorney General Pruitt, led the litigation challenge to EPA’s action. National environmental organizations supported EPA in the case, as they generally have done when EPA’s disapprovals of state regional haze plans have been challenged. Initially, Oklahoma and other challengers won a stay of the EPA rule from the US Court of Appeals for the Tenth Circuit, but then, in 2013, that court ruled against Oklahoma, and for EPA and its environmental-group supporters, on the case’s merits (State of Oklahoma v. EPA, 723 F.3d 1201 (10th Cir. 2013)). The US Supreme Court in 2014 declined Oklahoma’s request to review the Tenth Circuit’s decision.

Particularly in light of Attorney General Pruitt’s experience, many expect that in the new administration, EPA will allow states greater flexibility. BART plans are now in place for most states — in some cases because of EPA approval of state plans, in other cases because EPA imposed its own federal BART plans. But in some states, BART requirements are subject to continuing litigation or otherwise remain unresolved. And a new phase of regional haze regulation now looms on the horizon: development of new “reasonable progress” state plans (due in 2021) that will be designed to achieve continued progress toward natural visibility conditions in national parks and other protected federal lands.

Litigation on EPA’s disapproval of a Texas reasonable-progress plan already has been pending in the US Court of Appeals for the Fifth Circuit for nearly a year. In July, that court stayed the effectiveness of the January 2016 EPA rule that disapproved major elements of Texas’s plan and substituted a federal plan with far more demanding — and far costlier — control requirements for coal-fired power plants. After the November 2016 elections, the federal government asked the court to return the rule to EPA for further consideration, while the state of Texas and industry parties in the case have asked the court to invalidate the rule. The court is considering the parties’ competing motions.

While the Texas case moved forward, the Obama EPA took one of its last regulatory actions: publication, just 10 days before President Trump’s inauguration, of a broad new rule revising the agency’s underlying regional haze regulations, with a focus on reasonable progress requirements. In line with many of EPA’s state-plan disapproval actions, parts of this new rule seek to establish a relatively prescriptive approach that could constrain state discretion. Once presidentially appointed decision-makers take the reins at EPA, they will need to consider how best to address this last regional haze initiative of the Obama administration.

Will Scott Pruitt’s appointment as EPA administrator usher in a new federal policy on regional haze regulation under the Clean Air Act — an approach under which state determinations could find a friendlier reception at EPA? If so, the possibility of a more cooperative “cooperative federalism” in regional haze regulation may become a reality.