The U.S. Supreme Court announced yesterday that it would review a clean air case that could determine when the federal government can overrule state environmental decisions. The case concerns the Red Dog mine in Alaska, which produces zinc and lead. Two years ago, when the mine sought to build a new diesel generator, the state Department of Environmental Conservation agreed to allow the company to refit all of its generators with a low-cost pollution-control system to cut nitrogen oxide emissions. The U.S. EPA overruled that decision, ordering the company to instead install newer technology on the seventh generator, as mandated under the federal Clean Air Act’s New Source Review rule. The state argued that its plan would save money and cut overall emissions from the mine, but lost its case in both U.S. district court and in the 9th U.S. Circuit Court of Appeals. The high court will hear the case as part of its fall docket.