Federal regulators say they will let Arkansas enforce a portion of its own haze-reduction program, prompting criticism from environmentalists who say the plan is too weak.
The U.S. Environmental Protection Agency said Monday it had approved Arkansas' proposal for reducing nitrogen oxide, which with sulfur dioxide contributes to haze.
The Clean Air Act targets haze in national wildlife areas. The EPA in 2012 took issue with part of Arkansas' plan and set up its own after the state never resubmitted a new one. The federal plan imposed limits on specific power plants while the state wanted to let utilities "trade" emissions allowances.
The Sierra Club says the state plan, now approved, dismantles clean air protections. It had said previously that nitrogen oxide contributes to ground-level ozone that can be hazardous.