A federal appeals court ruled today that U.S. EPA must re-examine how it implements standards for fine particulates emitted by power plants, boilers and motor vehicles.

The three-judge panel of the U.S. Court of Appeals for the District of Columbia Circuit rejected EPA's argument that it is required under the Clean Air Act to use a less stringent implementation regime for fine particulates than it is for more coarse -- and less dangerous -- particles.

Today's ruling means EPA must look again at the implementation of the existing standards. Separately, the agency recently set new standards for fine particulate matter, or PM 2.5, that cover particles smaller than 2.5 micrometers in diameter (Greenwire, Dec. 14, 2012).

The Natural Resources Defense Council and Sierra Club had said states have too much flexibility, which means that in some cases standards are not being met. They challenged two George W. Bush-era rules, one from 2007 and one from 2008, that laid out how fine particle standards last set in 1997 should be implemented.

The environmental groups argued that EPA ignored language in the Clean Air Act as amended in 1990, which stated that particulate matter implementation is addressed in a different section of the statute than implementation requirements for other types of pollution.

The statute's language specifically dealing with particulate matter is stricter and gives states less leeway.

EPA said the Clean Air Act language raised by the environmental groups applies only to implementation of standards for coarse particles, otherwise known as PM 10.

In today's ruling, the court held that the Clean Air Act did not require EPA to handle fine particulate matter differently from the coarser pollutants. References in the statute to PM 10 indicate Congress was referring to particulate matter in general, which would include PM 2.5.

EPA had offered only "several unconvincing arguments" to support its theory that Congress intended for PM 2.5 to be dealt with differently from PM 10, Judge Karen Henderson wrote in the opinion.

The panel agreed with Paul Cort of Earthjustice, who during October's argument repeatedly made the point that PM 2.5 is included in the statutory definition of PM 10 (Greenwire, Oct. 17, 2012).

The court also rejected EPA's suggestion that the environmental groups' challenge was untimely because it should have been filed when the 1997 standards were first finalized.

Cort hailed today's decision as a "good day for clean air." It could force some jurisdictions that have yet to attain the 1997 standards to come up with new, more rigorous plans if they want more time, he added.

"It gives them less flexibility," he said.

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