A judge has ruled that Ohio is violating the federal Clean Air Act by letting small businesses ignore air-pollution limits.

The decision by Magistrate Mark R. Abel in U.S. District Court strikes down a 2006 state law that lets gas stations, auto-body shops and other small sources of air pollution use less than the best-available scrubbers and filters.

The exemption applied if a business emits less than 10 tons of air pollutants a year. The limit before the 2006 law was 1.8 tons.

The Ohio Environmental Protection Agency and industry groups had said the state law would cut costly and unnecessary delays in handing out air-pollution permits to new businesses that emit tiny amounts of pollution compared with big factories and power plants.

A small auto-body shop, for example, emits 3 tons of pollutants a year, while a power plant can spew more than 100,000 tons.

But in a lawsuit filed in September 2008, the Sierra Club argued that the Ohio EPA never got the U.S. EPA's approval to change its standards. The Sierra Club said the exemptions would worsen smog and soot in Ohio cities, including Columbus.

"The state of Ohio said, 'All of these small sources of pollution don't matter,'  " said David Altman, the Sierra Club's attorney. "That's not how it works when you're dealing with something as important as clean air."

Abel ruled that the exemptions the state granted businesses were illegal because they violated air-pollution limits set in Ohio's implementation plan. That plan is a legally binding agreement between the state and federal governments that outlines how the Ohio EPA will enforce the federal Clean Air Act. Any changes must be approved by the U.S. EPA.

"The state violates an emission standard or limitation each time it fails to enforce it," Abel wrote in the ruling, which was issued Tuesday.

He ordered the EPA to stop using the 10-ton exemption. Ohio EPA spokeswoman Heidi Griesmer said the agency will comply.

Griesmer said the Ohio EPA does not know how many businesses it granted exemptions to or how they affected air pollution. She said the agency doesn't know whether it will have to re-examine those exemptions.

The Ohio EPA did ask the U.S. EPA for permission to change its state implementation plan. In June 2008, U.S. EPA officials said Ohio first must show how the 10-ton standard wouldn't increase pollution.

Griesmer said the Ohio EPA hasn't sent that information to the U.S. EPA, and she did not know when it would be sent. U.S. EPA officials did not return calls seeking comment.

Jack Pounds, president of the Ohio Chemistry Technology Council, which represents chemical plants, said the law's sole purpose was to eliminate months-long reviews that the state conducts to determine which pollution-control devices are best. He said the delays mean lost time and money.

"Responsible businesses are not looking for loopholes to emit more air pollution," Pounds said. "We're looking for a process that's less costly and more efficient."

Altman said it was the Ohio EPA's job to show that small businesses wouldn't make air pollution worse, and the agency either could not or would not do it.

Ohio was clearly flouting federal law, he said.

shunt@dispatch.com