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CHEYENNE — It's ozone season in western Wyoming's Upper Green River Basin, but the weather so far hasn't been quite right to turn pollution from natural gas production into high levels of the irritating gas on the ground.

Ozone has been a perennial problem in the basin for several winters. Temperature inversions, which is cold air trapped by warmer air from above, combined with sunshine reflected off ground snow can trigger atmospheric chain reactions that turn gas-development pollution into ozone.

This winter, pockets of snow exist amid the sagebrush, but the wide expanses of snow said to be key to ozone formation aren't there yet. Usually Pinedale has more snow on the ground by this point in the winter.

"It feels strange," said Linda Baker with the Upper Green River Alliance.

But a snowstorm followed by a spell of clear, still weather could change things quickly. The Wyoming Department of Environmental Quality and companies that extract natural gas in the Pinedale area said they're ready if that happens.

"It's tough because we need the snow, we want the snow, but we don't want the ozone. We're continuing to always reduce our emissions, our impact," said Randy Teeuwen, spokesman for Calgary-based Encana.

The department planned a public meeting Tuesday to discuss developments and take ozone-related questions at the Sublette County library in Pinedale.

Last winter, ozone levels in the area soared above levels normally seen in big cities during the summer. Levels in the basin even surpassed any seen in smoggy Los Angeles in all of 2010, and state officials urged schools to keep children indoors during recess. The elderly and people with respiratory conditions also were told to stay inside.

Some people complained of itchy eyes and nosebleeds.

The Department of Environmental Quality has set up a daily forecast that will inform people when conditions will be ripe for high ozone and whether companies will need to scale back operations. The department has been working with Pinedale radio station KPIN to announce daily forecasts for ozone.

There have been no warnings for high ozone yet.

"We still have our ozone contingency plans in place, so if an advisory is issued we are prepared to act immediately," said Darci Sinclair, a Shell spokeswoman who also spoke on behalf of Ultra and QEP Energy.

The three companies operate the roughly 1,400-well Pinedale Anticline gas field just south of Pinedale. South of the anticline, Encana is the main operator in the Jonah Field, home to some 1,500 gas wells. The fields ranked sixth and fifth, respectively, among U.S. gas fields for production in 2009.

State regulators have not yet required companies to curtail operations when conditions are ripe for high ozone. Instead, 26 companies that operate in the basin have agreed to voluntary measures such as shutting off idling engines and refueling after ozone levels have peaked for the day.

Pinedale Anticline operators are looking ahead to plans to extend lines into the gas field to provide power for equipment for wastewater disposal wells, tank batteries and central gathering facilities. In each case, the imported power would eliminate the need for gas-fired generators that release the pollutants that can create ozone.

Environmentalists recognize that while the power lines would reduce pollution locally, they would create electricity demand met by coal-fired power plants elsewhere, said Baker.

"So are we trading one emission source for another?" she said.

Power lines also tend to frighten off sage grouse, which avoid places that offer high perches for eagles and other raptors.

State regulators will be taking into account two significant developments with ozone over the past year.

In September, President Barack Obama overruled the Environmental Protection Agency and scientific advisers by scrapping plans to lower the nationwide ozone limit. In December, the EPA announced it was moving ahead with a proposed ozone nonattainment designation for the Upper Green River Basin, a development that could bring more regulatory force to the area to curb ozone pollution.

The EPA expects to formalize ozone nonattainment areas nationwide by the end of May.