More than 100 million people living in 46 metro areas are breathing air that has gotten too full of soot on some days, and now those cities have to clean up their air, the Environmental Protection Agency said Monday.

The EPA added 15 cities to the sooty air list, mostly in states not usually thought of as pollution-prone, such as Alaska, Utah, Idaho and Wisconsin. That's probably because of the prevalence of wood stoves in western and northern regions, a top EPA official said.

But environmentalists said the EPA was only doing half its job on soot-laden areas, letting some southern cities with long-term soot problems — such as Houston — off the hook.

The EPA notified elected officials in 211 counties in 25 states that their air violated newly tightened daily standards for fine particles of pollution from diesel-burning trucks, power plants, wood-burning stoves and other sources. Those particles, often called soot, can cause breathing and heart problems.

These lists of what EPA calls "nonattainment areas" are important because regions that have air that is too sooty must come up with plans by 2012 on how to clean it and then do it by 2014. When old power plants and factories in these areas expand or do major refurbishing, they have to show EPA that it would not further pollute the air. It could mean also controls on vehicle emissions and regions having to take pollution into effect when they build new roads.

Fifty-four counties that didn't violate soot standards in 2004 — the last time EPA put out such a list — now do. They include areas around Fairbanks and Juneau, Alaska; Nogales, Ariz.; Pinehurst, Idaho; Davenport and Muscatine, Iowa; Klamath and Oakridge, Ore.; Provo and Salt Lake City, Utah; Seattle, Wash.; Green Bay, Madison, and Milwaukee, Wis., and the Logan, Utah, area that also includes part of Franklin County, Idaho.

The air is getting cleaner, but the daily soot standards were made nearly 50 percent tougher in 2006, said Robert Meyers, the principal deputy assistant administrator for air and radiation at EPA.

Since 2006, EPA has had two sets of soot standards and this list only looks at one of them. There are daily air quality standards and long-term yearly standards. The Bush Administration tightened the daily standard, but not the long-term one, despite EPA's science advisers' recommendation to do so.

The EPA came out with a new list based on the tightened daily standards, but doesn't plan to take another look at cities violating the longer-term standards, Meyers said. That list was last completed in 2004 and 95 million people lived in cities considered too full of soot.

Because of that, at least five regions, including Houston, that did violate the yearly soot standards, don't have to do anything about it and residents are not told there's a problem, said Frank O'Donnell, president of the environmental group Clean Air Watch

"EPA has failed to protect many millions of people from deadly particle soot by pretending that areas are clean where the air is actually dirty," O'Donnell said. "The poster child for this is Houston."

"It is a very bad holiday gift to breathers in cities like Houston," O'Donnell said. "The Bush administration has given them the gift of dirty air."

The other areas left off the EPA's list, but still violating annual standards, include Augusta and Columbus, Ga.; Greenville, S.C., and Fairmont, W.Va., O'Donnell said.

Meyers said that's not the case.

"The overall trend is encouraging," Meyers said in a telephone interview "We're having success in controlling things like diesel particles from trucks."