Given that temperatures lately have barely climbed out of the single digits, it might seem odd to hope for a cooler summer.

Otherwise, the seven-county Pittsburgh metropolitan area probably will fail to meet federal health standards for smog, and that could mean stricter air-pollution controls on utilities, industries and vehicles.

That's a likely consequence of a new U.S. Environmental Protection Agency rule that will reclassify the seven-county Pittsburgh metropolitan area and more than a dozen other areas nationwide that are failing to meet the federal health standard for ozone, the primary component of smog.

The Pittsburgh region, now a "non-attainment" area, will be reclassified as a "moderate non-attainment" area for ground-level ozone.

Under the new classification, if the region fails to reduce ozone levels by 2010, it could be bumped into a "serious non-attainment" classification that would mandate stricter emissions reductions and controls on stationary and mobile pollution sources.

The rule, issued to comply with a 2006 federal court decision in a case brought by environmental groups against the EPA, would revise classifications made under the 1997 eight-hour ozone standard. The rule will go into effect when it is published this week.

Christopher Cripps, an environmental engineer in EPA's regional office in Philadelphia, said the Pittsburgh region's three-year ozone value for 2005-07 was 87 parts of ozone per billion parts of air. The 1997 federal standard was 80 parts per billion.

"Pittsburgh is close to meeting the old standard, and that makes it difficult to say what's going to happen, but meeting the standard will be difficult," Mr. Cripps said. "This summer's air-quality data will be critical."

Ozone is formed when volatile organic compounds, or VOCs, and nitrogen oxides in the air react with sunlight. Sunny, hotter summers produce higher levels of ozone, a colorless gas which can cause breathing problems, particularly for people who have chronic lung diseases, the elderly and small children -- an at-risk group that numbers 500,000 in the region.

After the hot summer of 2003, the Pittsburgh region's ozone value was 94 parts per billion. It went down to 83 parts per billion for the three years ending in 2006, but in 2007 there were eight ozone readings from 87 to 99 parts per billion on seven days.

Mr. Cripps said the region has already implemented a number of emissions controls, including vehicle exhaust inspections, gas station vapor recovery pumps and industry pollution limits. If the region can't meet the federal smog standard and is bumped to serious non-attainment, it will have to reduce VOC emissions by 15 percent, and the EPA can impose limits on emissions from new industries and road building and additional highway and off-road vehicle emissions controls.

The original EPA smog classifications were driven as much by politics as pollution or weather, said David Baron, an attorney with Earthjustice, which along with four other environmental groups challenged the original Clean Air Act classifications for Pittsburgh and 13 other regions, seven of those in California.

"It was a political decision by the EPA to apply the weakest controls wherever it could," Mr. Baron said. "But we thought that approach was illegal, and the court told them that, too. By proposing this rule, the EPA, limping to the finish line, is finally getting around to fixing that violation.

"In general this puts Pittsburgh and the other communities on a much stricter track toward clean air. The EPA approach gave them a lot of leeway and did little to protect public health."

The Pennsylvania Department of Environmental Protection said ozone levels across the state have dropped by 10 percent during the past five years because of cleaner-burning fuel and cleaner vehicle emissions and a more-comprehensive vehicle-inspection program.

Guillermo Cole, an Allegheny County Health Department spokesman, said the region's air also will be helped by implementation of the federal Clean Air Interstate Rule, which will limit pollution from coal-burning power plants in the Ohio River Valley west of Pittsburgh. It's estimated that a third or more of the ozone pollution in southwestern Pennsylvania is transported from those power plants by prevailing winds.

Last year only one of four ozone monitors in Allegheny County registered ozone levels higher than the federal standard. But that monitor, in Harrison, north of the city along the Allegheny River, is indicative of wider air-quality problems, Mr. Cripps said.

"The Harrison monitor only samples one area, but you can't put an ozone monitor on every street corner," he said. "If you've got one monitor showing high ozone, the region could well have a problem that is more widespread."

Allegheny, Armstrong, Beaver, Butler, Fayette, Washington and Westmoreland counties were designated as being in "non-attainment" of the federal smog standard in 1991.

Reflecting new health research, the EPA issued slightly tighter ozone standards of 75 parts per billion in May 2008. Classifications under those standards have not been finalized, but the EPA estimates that 345 counties nationwide -- including those in the Pittsburgh region -- will not meet the new standard.