Early Friday afternoon, American Electric Power spokesman Phil Moye saw the plume rolling in from his office on the 11th floor of the Chase Building in downtown Charleston.

"When you look up the Valley, it's just a blue haze all the way up," Moye said.

Moye and other AEP officials said their giant John Amos Power Plant had nothing to do with the mysterious cloud that hung over the Kanawha Valley most of the afternoon.

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AEP officials say they believe their John Amos Power Station was operating normally on Friday, but state inspectors are examining whether any problems at the plant contributed to Friday’s blue haze problem. The plant is among the region’s largest polluters, but Columbus, Ohio-based AEP is spending hundreds of millions of dollars to greatly reduce emissions.

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But by early Friday evening, state Department of Environmental Protection officials had focused their investigation on the Amos facility, located just across the Kanawha River from Poca.

DEP inspectors flew over the area in a state helicopter. They saw a string of plumes - presumably from other coal-fired power plants along the Ohio River to the northwest - converge, combine and, perhaps, concentrate with emissions from Amos.

Inspectors also saw a thick, low-hanging layer of warm air, an unusually potent temperature inversion that appeared to be trapping plant pollutants over the river valley.

No injuries or serious health effects from the blue, chlorine-smelling plume were reported to area hospitals.

Kanawha County emergency officials did not order a formal shelter in place. But they did recommend that residents not "voluntarily prolong exposure because the substance is still unknown." That recommendation was lifted Saturday afternoon, after the haze appeared to have cleared out overnight.

Now, DEP investigators will continue to try to piece together exactly what happened.

Agency officials will study aerial photographs. Engineers will examine complex plant operational monitoring reports. Inspectors will interview plant personnel.

Was it just normal emissions from Amos, held over the valley longer by an especially strong weather system? Did AEP have a mishap that the company just hasn't identified yet? Or was it some combination of the two?

"There could or there could not be anything wrong with the facility," said John Benedict, director of the DEP Division of Air Quality. "We really have to look at the data."

Meanwhile, new DEP data obtained Saturday provided a glimpse of the air-quality impacts of whatever happened on Friday.

Starting about 1 p.m., concentrations of particulate matter - very fine smoke, soot and dust that are linked to a variety of respiratory problems - skyrocketed, according to data from a DEP monitoring station in downtown Charleston.

Average particulate matter concentrations between 1 p.m. and midnight Friday were four times higher than those the previous 12 hours, according to the DEP data. Concentrations peaked at 105 micrograms per cubic meter at 6 p.m., the DEP data showed.

Particulate matter is likely just one of an unknown number of chemicals that hung over the Valley on Friday. But it's a pollutant that DEP closely monitors, and provides an example of what happens when temperature inversions form a lid over the area.

Benedict said that the concentrations were still within legal limits, but were "consistent with the event that occurred."

A local powerhouse

 The John Amos plant, named for a former AEP executive and legislator, is the largest generation plant in the Columbus, Ohio-based utility's system. Completed in the early 1970s, the facility can churn out up to 2,900 megawatts of electricity.

Almost every year, the coal-fired plant ranks as the top source of air pollution in West Virginia. In 2005, the plant released nearly 18 million pounds of toxic chemicals from its stacks, according to the U.S. Environmental Protection Agency's Toxics Release Inventory.

Parent company AEP has also spent hundreds of millions of dollars to try to reduce the pollution from Amos.

Starting in 2002, it installed new equipment to greatly reduce nitrogen oxide emissions that contribute to smog. And AEP is nearly complete on the addition of sulfur dioxide scrubbers, a project that alone cost the company more than $1 billion.

These new pollution controls have not been without their problems. Both the nitrogen oxide controls and the scrubbers in use at Amos have been linked to pollution problems at other plants.

"When you look up the Valley, it's just a blue haze all the way up," Moye said.

Moye and other AEP officials said their giant John Amos Power Plant had nothing to do with the mysterious cloud that hung over the Kanawha Valley most of the afternoon.

Up and down the river, industrial facilities all offered similar answers. No leaks at the Bayer plant in Institute. Nothing wrong at Dow in South Charleston. And at John Amos? "All of our monitoring levels are fine," Moye said.

But by early Friday evening, state Department of Environmental Protection officials had focused their investigation on the Amos facility, located just across the Kanawha River from Poca.

DEP inspectors flew over the area in a state helicopter. They saw a string of plumes - presumably from other coal-fired power plants along the Ohio River to the northwest - converge, combine and, perhaps, concentrate with emissions from Amos.

Inspectors also saw a thick, low-hanging layer of warm air, an unusually potent temperature inversion that appeared to be trapping plant pollutants over the river valley.

No injuries or serious health effects from the blue, chlorine-smelling plume were reported to area hospitals.

Kanawha County emergency officials did not order a formal shelter in place. But they did recommend that residents not "voluntarily prolong exposure because the substance is still unknown." That recommendation was lifted Saturday afternoon, after the haze appeared to have cleared out overnight.

Now, DEP investigators will continue to try to piece together exactly what happened.

Agency officials will study aerial photographs. Engineers will examine complex plant operational monitoring reports. Inspectors will interview plant personnel.

Was it just normal emissions from Amos, held over the valley longer by an especially strong weather system? Did AEP have a mishap that the company just hasn't identified yet? Or was it some combination of the two?

"There could or there could not be anything wrong with the facility," said John Benedict, director of the DEP Division of Air Quality. "We really have to look at the data."

Meanwhile, new DEP data obtained Saturday provided a glimpse of the air-quality impacts of whatever happened on Friday.

Starting about 1 p.m., concentrations of particulate matter - very fine smoke, soot and dust that are linked to a variety of respiratory problems - skyrocketed, according to data from a DEP monitoring station in downtown Charleston.

Average particulate matter concentrations between 1 p.m. and midnight Friday were four times higher than those the previous 12 hours, according to the DEP data. Concentrations peaked at 105 micrograms per cubic meter at 6 p.m., the DEP data showed.

Particulate matter is likely just one of an unknown number of chemicals that hung over the Valley on Friday. But it's a pollutant that DEP closely monitors, and provides an example of what happens when temperature inversions form a lid over the area.

Benedict said that the concentrations were still within legal limits, but were "consistent with the event that occurred."

A local powerhouse

 The John Amos plant, named for a former AEP executive and legislator, is the largest generation plant in the Columbus, Ohio-based utility's system. Completed in the early 1970s, the facility can churn out up to 2,900 megawatts of electricity.

Almost every year, the coal-fired plant ranks as the top source of air pollution in West Virginia. In 2005, the plant released nearly 18 million pounds of toxic chemicals from its stacks, according to the U.S. Environmental Protection Agency's Toxics Release Inventory.

Parent company AEP has also spent hundreds of millions of dollars to try to reduce the pollution from Amos.

Starting in 2002, it installed new equipment to greatly reduce nitrogen oxide emissions that contribute to smog. And AEP is nearly complete on the addition of sulfur dioxide scrubbers, a project that alone cost the company more than $1 billion.

These new pollution controls have not been without their problems. Both the nitrogen oxide controls and the scrubbers in use at Amos have been linked to pollution problems at other plants.

Unintended consequences

To comply with the 1990 Clean Air Act, AEP installed sulfur dioxide scrubbers at its James M. Gavin Plant in Cheshire, Ohio, in the mid-1990s. Technically, scrubbers are known as flue gas desulfurization. A mixture of limestone and water is sprayed into plant emissions to capture sulfur dioxide.

In 2001, AEP began operating new nitrogen oxide controls at Gavin. These controls are called selective catalytic reduction units, or SCRs. They use a catalyst, usually anhydrous ammonia, to turn nitrogen oxides into nitrogen and water.

If not operated a certain way, scrubbers can create too much oxygen, turning sulfur dioxide into sulfur trioxide. This in turn can form a liquid aerosol form of sulfuric acid. This mist often causes a blue haze.

SCRs can also cause acid plumes and, when operated in conjunction with scrubbers, can greatly increase the formation of acid mist, according to court records.

At Gavin, Cheshire residents, across the Ohio River from Mason County, began to complain of watery eyes, headaches and breathing problems when plumes of this mist would touch town.

In April 2002 - just months after a federal report found the acid plumes to be a public health threat - AEP announced that it would pay $20 million to buy most of Cheshire.

Four years later, AEP agreed to a separate settlement with remaining Cheshire residents, who sued to force Gavin to reduce its pollution.

A similar suit is pending in federal court in Cincinnati over nearly identical pollution problems at Duke Power's William H. Zimmer Power Station in Moscow, Ohio.

Charleston lawyer Ben Bailey, who represented Cheshire residents, said Saturday similarities with the Gavin incidents raised questions about what was going on at Amos.

"The parallels make one wonder," Bailey said.

'The mysterious blue haze'

At the Amos plant, officials are running the SCR pollution controls. But they have yet to complete the scrubbers and, according to DEP inspectors, are not yet testing those devices.

The SCRs alone could create a blue-haze problem, officials said, but AEP experts don't think that's what happened.

"All we can do really is look at the operational data at the plant," Moye said Friday night. "And we just really aren't seeing anything that could have contributed to the haze in the valley."

Complicating matters for investigators is that, while the haze appeared blue, most residents reported a strong chlorine bleach smell. A chlorine cloud would be more likely a yellowish color. And a sulfuric acid plume from a power plant would probably not smell like bleach.

State emergency responders took samples Friday evening, and their analysis did not indicate the presence of a sulfuric acid problem, according to Kanawha County emergency services director Dale Pettry. More detailed samples to determine what was in the chemical cloud are still being analyzed.

"The mysterious blue haze remains just that - mysterious," said County Commissioner Kent Carper.

Benedict, the DEP air director, said that unusual weather conditions probably trapped in the valley a variety of other pollutants that typically disperse high in the air. It's hard to tell what mix occurred, what sort of reactions developed, or what smells were created. But there's no question that weather made matters worse.

Usually, air closer to the surface of the Earth is warmer than the air above it. That's because it is heated from below as sunlight warms the Earth's surface. Under certain conditions - such as when a high-pressure system persists, as happened in the Valley late last week - the air flips so colder air is closer to the ground.

When this happens, a layer of warm air above that lower cold air can trap pollutants like a lid on a jar.

Dave Marsalek, a National Weather Service meteorologist, said that is partly what happened in the Valley on Friday. There was an especially strong and thick inversion, located very low to the ground, an estimated 1,500 to 2,000 feet up, he said. There was also little wind, further eroding any dilution of pollution.

"They are common, but this one was particularly strong," Marsalek said. "That's a pretty shallow layer of atmosphere that this material - whatever it was - was confined to."

To contact staff writer Ken Ward Jr., use e-mail or call 348-1702.