Maryland environmental regulators are asking their federal counterparts to crack down on 19 coal plants in five other states whose emissions — carried hundreds of miles by the wind — make the air here unhealthy to breathe on hot summer days.
The plants have spent billions of dollars on technology to reduce pollution, but according to Maryland officials, they don't use it every day during the summer, when heat and sunshine cause the pollutant ozone to form and make air quality its worst.
Ben Grumbles, the state's environment secretary, is asking the U.S. Environmental Protection Agency to step in before this summer.
"We're saying to EPA we know for a fact those power plants have the existing control technologies, they have installed them, but for whatever reason, they're not running them every day during the ozone season," Grumbles said. "That is one very easy way for downwind states like Maryland to benefit."
Northeastern and Mid-Atlantic states have long pressured federal officials and Midwest states to reduce the pollution that blows eastward.
Maryland's petition filed Wednesday presents a relatively new strategy in requiring the states to comply with the federal Clean Air Act, and it comes a month after New York and other states sued the EPA over interstate air pollution.
Maryland environmental officials estimate that 70 percent of this state's ozone pollution comes from upwind states. Such air pollution contributes to health problems that include respiratory illness and heart disease.
"Any effort to clamp down on that noxious pollution can only be of benefit to breathers in Maryland," said Frank O'Donnell, president of Clean Air Watch, an advocacy group in Washington. "There are multiple tools within the Clean Air Act to deal with interstate pollution."
Maryland's petition concerns 36 coal-fired units at 19 plants in Indiana, Kentucky, Ohio, Pennsylvania and West Virginia. Grumbles said the state has been tracking data and air pollution models for the past three years to learn that efforts to cut pollution have fallen short of their potential.
Coal plants across the country have been required to invest in technology to remove key pollutants from their exhaust — sulfur dioxide and nitrogen oxides, which react with other compounds in the atmosphere to form ozone.
In Maryland, regulations imposed last year require that power plants use the technology daily during the summer, when the weather multiplies the ozone pollution in the air and prompts air-quality health alerts.
In other states, however, plants don't have to use the pollution controls every day as long as their average output of the noxious gases remains under federal standards.
"We're not asking for anything that we're not already doing in Maryland," Grumbles said.
One air-quality advocate noted that the petition does not mention a Pennsylvania coal plant that two states have asked EPA to crack down on. Earlier this year, Connecticut and Delaware officials both asked the agency to require pollution controls at the Brunner Island Power Plant south of Harrisburg, Pa.
"We certainly think that plant impacts Maryland, as well," said Mark Kresowik, regional deputy director for the Sierra Club's Beyond Coal campaign. Still, he said, the organization is "encouraged" by Maryland's petition.
The state has asked the EPA to act by May, before next summer's "ozone season" begins.
Grumbles said he hopes the Obama administration acts on the request soon, but if it does not by Jan. 20, the state plans to continue to press the issue with the new administration of President-elect Donald Trump.
The petition fits "hand in glove" with a pending call for the EPA to add nine states to a regional commission focused on reducing interstate pollution, Grumbles said. Maryland was among eight states that asked the agency in 2013 to expand the group to include Illinois, Indiana, Kentucky, Michigan, Ohio, Tennessee, Virginia, West Virginia and North Carolina.
New York and five other states sued the EPA in federal court in New York City last month, demanding that it act on that request.
At that time, Grumbles said the state would not join the lawsuit and would instead focus on "working outside of the courtroom ... to reduce interstate smog."