For the third time in 12 days, authorities have issued an ozone advisory for the Pinedale area.

The Wyoming Department of Environmental Quality, in conjunction with the Wyoming Department of Health, is warning Sublette County residents that ozone levels could hit "unhealthy" levels today, as defined by the federal Environmental Protection Agency.

At ground level, ozone is a potentially poisonous gas that in high enough concentrations can cause breathing problems in children, the elderly and those with pre-existing respiratory conditions.

Inhabitants in the Pinedale region who are potentially sensitive to the pollutant are advised by the DEQ to limit strenuous or extended outdoor activities today.

An ozone advisory was also issued for the same area Monday, and 11 days prior, last month. The warning in February was the first of its kind in the Cowboy State.

From now on, the DEQ will issue ozone warnings one day at a time, so there is no confusion about when the advisories start or end, said Keith Guille, a DEQ spokesman.

"It's similar to the way they do it in Denver and other major metropolitan areas," Guille said. "We will issue each advisory the day before, for the following day only."

The air quality warnings will be sent to media outlets statewide, as well as to all local and regional newspapers, radio stations and TV stations, Guille said.

The Air Quality Division of the DEQ is in the process of conducting a study of wintertime ozone formation in the Upper Green River Basin.

Ozone gas is created when sunlight hits hydrocarbons and oxides of nitrogen that are present in the air. Both are pollutants created chiefly by the burning of fossil fuels at ground level.

Heavy snow cover in the Upper Green River valley, combined with slow wind speeds and strong temperature inversions seem to increase ozone production around Pinedale, said David Finley, the air quality administrator for the DEQ.

A temperature inversion occurs when a warm air mass sits atop a cold mass, compressing it toward the earth. The inversion can have the effect of trapping the air in the valley.

While some of the hydrocarbon and NOX pollutants come from other sources in the Upper Green, a significant portion, it appears, are being produced by gas extraction activities in the Jonah and Pinedale Anticline fields, Finley told the Star-Tribune in February.

"Pollutants are most certainly being created by gas production activities there," he said. "They're also emitted by cars and by fossil fuel combustion - but the oil and gas development activities out there are a large source of the volatile organic compounds," Finley said.

Randy Teeuwen, a spokesman for EnCana Oil and Gas Inc., which has active gas extraction operations in the Jonah field, said he hopes people understand that his company is genuinely interested in improving air quality in Sublette County.

"It's an issue that we are concerned about, just like everybody else," Teeuwen said. "We're part of the community as well, and we breathe the same air."

EnCana, he said, is continuously working to implement the most up-to-date, least-polluting equipment available. It is also working toward consolidating field operations in order to create fewer sources of possible emissions.

"I'd like people to know we are working on this. We're being very aggressive about it," Teeuwen said. "We, as an industry, are very heavily regulated. We work with the DEQ regularly. We're in constant communication with the DEQ, and we have to comply with the regulatory agencies."

Even though EnCana relies upon oil and gas consumption to turn a profit, Teeuwen said polluting less through better efficiency is the responsible thing for his company, and for everyone else, to strive for.

"In the world we live in today, where we're so heavily dependent on fossil fuels, one of the most important things everybody needs to do is work on reducing our consumption," Teeuwen said.

Bruce Pendery, air quality program director for the Wyoming Outdoor Council, said it's important that companies like EnCana work to reduce emissions, but it's also important the public understands what those reductions mean in the context of rapidly expanding development of the gas fields.

Even if each individual well is polluting less, the total pollution can increase as more wells are added to energy fields, he said.

"If you have 500 sources of emissions instead of 50 sources of emissions, even if those 500 sources have strong efforts to control pollution, like EnCana is claiming, the increased sources can just overwhelm and displace any efforts to control the pollution," Pendery said. "In the Pinedale area, the scale is so accelerated that even if there are good faith efforts to control emissions, those efforts are simply being swamped."

Pendery said the gas producers need to take aggressive actions to reduce emissions, as Teeuwen suggests they are, but they also might need to apply the brakes on expansion efforts.

"They might need to go slower," he said. "Nobody out there even wants to consider a reduced pace of development, but everything needs to be on the table. All options should be considered. Clearly, scaling back the pace of development should be one of those options."

There has not yet been an ozone advisory issued for Wednesday for the Pinedale region, and a spokesman with the DEQ said he couldn't predict whether there will be more warnings in the coming days, because changes in short-term weather conditions will change the ozone outlook.

Current information on ozone levels at the Air Quality Division's monitoring stations at Daniel, Jonah, and Boulder can be found at www.wyvisnet.com.

Environment reporter Chris Merrill can be reached at chris.merrill@trib.com or at (307) 267-6722.