The Hogan administration notified the federal Environmental Protection Agency Thursday that it plans to file a lawsuit alleging it has failed to act against states whose smokestack emissions pollute Maryland’s air.

In a letter to EPA Administrator Scott Pruitt, Maryland Environment Secretary Ben Grumbles charged that the Trump administration has failed to enforce mandatory provisions of the Clean Air Act despite evidence that five upwind states are illegally emitting nitrogen oxide that contributes to Maryland’s pollution problems.

The warning signals a new aggressiveness in Gov. Larry Hogan’s approach toward President Donald J. Trump, a fellow Republican whom he did not support in last year’s election.

Hogan spokeswoman Amelia Chasse said protecting Maryland’s air quality is a priority for the administration.

“We will take whatever steps are necessary to ensure that other states and the federal government are meeting their responsibilities," she said.

Jon Mueller, vice president of litigation at the Chesapeake Bay Foundation, praised the move.

“We join and wholeheartedly support Maryland in its effort to protect the health of its residents and the Chesapeake Bay against upwind, out-of-state power plants which choose to make higher profits rather than turn on their pollution controls during hot summer months,” Mueller said in a statement.

David Smedick, policy director for the Sierra Club’s Maryland chapter, said the organization welcomes the action.

“The next step is to pull the trigger and actually file suit,” he said.

Nitrogen oxide from air pollution, known as NOX, is one of the major contributors to nutrient pollution of the Chesapeake Bay. During hot weather, it also contributes to the formation of health-threatening ozone near the earth’s surface.

Grumbles’ letter says that Maryland presented the EPA last November with a petition asking it to rule that 36 power units at 19 plants in Indiana, Ohio, West Virginia, Kentucky and Pennsylvania are violating the “good neighbor provision” of the Clean Air Act.

Maryland contendsthat the EPA has failed to either uphold or deny Maryland’s claim and has not scheduled a hearing on the matter. The state said the EPA in January gave itself a six-month extension of the law’s 60-day deadline for responding to such allegations but then failed to meet a July 15 deadline to act on its petition.

The state alleges that pollution from those upwind states contributes significantly to Maryland’s inability to meet clean air standards for ozone.

Grumbles told The Baltimore Sun the notification is required before the state can file suit against a federal agency. He said the EPA has 60 days to decide how to respond before the state can go to court.

“This is an important step, and we’re willing to take all the steps we need to take,” Grumbles said. “Our message is that this is an important priority for us and we’re going to use all available tools to make clear air progress.”

If Maryland files suit against the EPA over pollution from out-of-state power plants, it will be only the second state to do so, Grumbles said. He said Connecticut was the first to sue the EPA for that reason, but that Maryland’s petition is much broader. Any suit would be filed in the U.S. District Court in Baltimore.

The threatened suit has the makings of a red-state/blue-state conflict. Maryland voted decisively for Democrat Hillary Clinton in the presidential election. The five states where Maryland wants the EPA to take action voted for Trump.

Under Pruitt, a former Oklahoma attorney general who was fierce critic of the EPA, the agency has taken a sharp turn in the direction of less regulation. Pruitt is known as a staunch defender of fossil fuels at a time when much of the world is shifting tow the use of less-polluting, renewable energy sources.

A spokeswoman said the EPA does not comment on matters involving litigation.

Grumbles said Maryland's notice comes after months of communication with EPA officials yielded no results.

About 70 percent of the ozone in Maryland’s atmosphere comes from out-of-state plants, Grumbles said. He said Maryland has been working with the other states to bring their power plants into compliance.

The Obama administration adopted tougher ozone standards in 2015. Grumbles said the out-of-state emissions, carried on the wind from the west, threaten Maryland’s efforts to comply with those regulations.

Grumbles said the power plant units where the state is asking EPA to enforce the clean air law are equipped with technology that controls the amount of nitrogen oxide . But he said those plants are not consistently using those controls. Maryland is asking the EPA to require the plants to use their pollution-control technology on a consistent basis.

“We’re not asking anything of them that we’re not already doing in Maryland,” Grumbles said.

The state’s petition does not ascribe motives to the plant operators, Grumbles said. But he said one reason might be to save money.

Mueller said the bay foundation estimates that the power plants earned an extra $24 million in profit in 2014 by not using the controls.

“They have old technology but they're not even using that,” Smedick said. “We believe they can upgrade and run that technology all the time.”

Smedick said ozone is a big problem in Maryland, especially Baltimore. The air quality index for metropolitan Baltimore Thursday was scored as Code Red, or unhealthy. Under a Code Red, people with lung problems or asthma, especially children, are warned to avoid heavy outdoor exertion. Healthy people are advised to reduce such activity.

“Ozone is great high in the atmosphere but down here it’s really bad to breathe in,” Smedick said. “It’s like getting sunburn on your lungs.”

Smedick said Maryland has seven coal-burning power plants, of which four do not have the most modern controls.

The Hogan administration rejected rules requiring those four to upgrade to the best technology, Smedick said. However, he said the administration did adopt rules that require all seven plants to use the technology they have in place during the summer months.

Sen. Paul Pinsky, one of the General Assembly’s most ardent environmentalists, said the administration made the correct decision in notifying the EPA of its intent to file suit. But the Prince George’s County Democrat expressed hope that the state will be equally tough on power plants in Maryland.

“I don’t want to deflect our own responsibility to clean up our own emissions,” he said.

mdresser@baltsun.com

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