Three coal-fired power plants in Arizona would need more pollution-trapping devices under a proposal released late Monday by the U.S. Environmental Protection Agency.
One is between Winslow and Holbrook, one on the Arizona-New Mexico border and a third east of Tucson.
The measure would "improve visibility and human health" at 18 national parks and wilderness areas, including Grand Canyon and the Petrified Forest, the EPA projected.
That would bring clearer views to some 11 million national park visitors in Arizona, the EPA stated.
There were no immediate estimates of cost on Tuesday.
Cholla Power Plant in Joseph City, owned by Arizona Public Service, is one of the nearest plants to Flagstaff and the Grand Canyon proposed for more pollution controls.
Specifically, the EPA would propose to cut 7,800 tons a year of nitrogen oxide emissions, a key ingredient in bad ozone -- or smog) at Cholla.
The EPA's proposal comes on the heels of litigation by nine environmental groups after the EPA missed legal deadlines for limiting pollution from Arizona power plants and factories.
The groups cheered Monday's announcement on Tuesday.
"This is a plan to finally get some very polluting coal plants out of the 1960s and '70s where they've been stuck," said Anna Frazier with Diné Citizens Against Ruining Our Environment (Diné CARE).
Fine-particulate pollution from the power plant in Joseph City likely contributed to 39 heart attacks and 460 asthma attacks annually, a study from the nonprofit Clean Air Task Force stated.
The EPA plans to make a final decision in November.