WASHINGTON — Federal courts heard two pollution cases Tuesday centered on whether Southern and Midwestern states should have to crack down on emissions from coal-fired power plants to help clear the air in Northeastern states.

In the U.S. Supreme Court, justices indicated they may reinstate an Obama administration rule that sought to impose tougher standards on 28 states accused of contributing to air pollution elsewhere. The court’s decision likely won’t be released for months, but justices appeared skeptical at times of arguments that the U.S. Environmental Protection Agency had overstepped its authority.

“It is what the statute says, and it seems to me that if the EPA had taken a different view, it would have been contrary to the statute,” said Chief Justice John Roberts, one of the conservative members of the court.

Although Maine was not a party to the cross-state pollution case pending before the Supreme Court, state Attorney General Janet T. Mills had supported the EPA’s position in a second case over national standards for mercury emissions from power plants. That case was heard in the U.S. Court of Appeals for the District of Columbia Circuit.

Both cases pitted coal-rich or coal-reliant states in the South and Midwest against Northeastern states struggling to meet federal air quality standards due, in part, to pollution drifting up the eastern seaboard.

Although separate, the two cases seek to test the scope of the federal government’s regulatory reach under the Clean Air Act, with the resulting verdicts likely to affect future regulation.

Arguing for the states opposed to the EPA’s cross-state pollution rule, Texas Solicitor General Jonathan Mitchell said the agency had violated its authority by imposing pollution-reduction plans on states without first allowing them to write their own plans. He also said the EPA left states “completely in the dark” by not setting emissions levels.

The challengers also suggested that the EPA was forcing some states to make aggressive changes – based on arbitrary cost standards – that were far above what was necessary to account for pollution in neighboring states.

Mitchell’s arguments, as well as those of a representative for energy utilities, resonated with Justice Antonin Scalia. But many of the other eight justices present – especially those from a more liberal judicial perspective – appeared skeptical of the challengers’ arguments.

Justice Elena Kagan stated that “the states that are required to do more are the states that haven’t done much already.”

Highlighting the regional nature of the issue, the governors of eight Northeastern states – including all of New England except Maine – are separately petitioning the EPA to impose stricter ozone pollution standards on nine upwind states. The other five New England states also were participants in the case heard Tuesday by the Supreme Court.

The Republican administration of Maine Gov. Paul LePage opted not to join either the petition or the cross-state air pollution case because Maine currently meets – or is “in attainment” of – federal standards for ozone. Ground-level ozone is a respiratory irritant created when nitrogen oxide and volatile organic compounds – the byproducts of vehicle exhaust and industrial emissions – combine with sunlight and oxygen.

Marc Cone, director of the Maine Department of Environmental Protection’s Bureau of Air Quality, said Tuesday that roughly 93 percent of the ozone pollution measured by the EPA in Maine in 2008 – the last year in which surveys were done – originated from outside of the state.

But the vast majority of that pollution was attributable to Northeastern states that already participate in a regional ozone-reduction plan; only a small portion of that pollution – less than 4 percent – was attributable to the nine states targeted by the petition.

“At this point in time, we do not see them as having a large contribution to our attainment status in this state,” Cone said. “We are in attainment.”

It is Maine’s attorney general – not the governor – who ultimately decides whether the state should become a party to federal legal cases, although the two offices typically collaborate.

The other federal case pending in Washington on Tuesday – which Maine did join – involved EPA rules that would require coal-fired power plants to reduce emissions of mercury, arsenic and other toxic substances.

In 2008, Maine and six other Northeastern states petitioned the EPA to take action on airborne mercury pollution stemming from other states. That petition led to the national standards now under scrutiny by the D.C. Circuit appellate court, which is the same court that struck down the cross-state pollution rule.

Mercury pollution in Maine comes from sources both within and outside of the state’s boundaries. Some of the mercury that taints Maine’s waterways – prompting fish consumption advisories on some rivers – stems from the days before state and federal regulations prohibited discharges of mercury-tainted waste from paper mills and other industrial factories.

But airborne mercury is a significant component of modern mercury pollution in Maine.

“By acting to protect one of the most vulnerable segments of our population – children – EPA has hewn closely to the goals of the Clean Air Act” and federal statutes, reads a brief filed with the court by Mills and 15 other state attorneys general.

“Given that 7 percent of women of childbearing age may already be exposed to dangerous mercury levels, the serious health effects of mercury contamination, and the limitations of the patchwork of fish consumption advisories and other controls in place, national regulation of (power plant) mercury emissions is not only ‘appropriate and necessary,’ it is imperative.”

Air pollution has emerged as a political issue in Maine in recent months.

The LePage administration angered some in the health and environmental community by seeking to exempt some Maine industries from having to purchase “offset” credits for emissions as part of the regional ozone reduction plan. The administration of Democratic Gov. John Baldacci sought similar but more limited exemptions.

Additionally, residents of Eliot, Maine, have asked the EPA to determine whether a coal-fired power plant in Portsmouth, N.H., is causing elevated levels of sulfur dioxide and health problems in the town.

Ed Miller, senior vice president for policy at the American Lung Association of the Northeast, said he was disappointed that Maine did not join the cross-state air pollution case or the EPA petition.

Miller said the lung association believes that the current ozone level standards are too high to adequately protect public health. So the fact that Maine is in compliance does not necessarily mean residents are not being exposed to unhealthy ozone levels, Miller said.

But the cross-border rule also addresses particulate matter – a key ingredient of smog – spewed by coal-fired power plants in other states.

“We are much stronger when all of the Northeastern states act in unity on these issues,” Miller said.

Kevin Miller can be contacted at 317-6256 or at:

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