State regulators have issued the first ozone advisories for the western Wyoming gas patch in more than two years and are telling people sensitive to air pollution to take precautions.
High levels of ozone are associated with smog, which smudges the sky in the Upper Green River Basin when conditions are right during the winter. Such conditions include snow on the ground, abundant sunshine, a temperature inversion and air pollution including nitrogen oxides and volatile organic compounds.
On Sunday and Monday, the Wyoming Department of Environmental Quality issued ozone advisories for Monday and Tuesday. The advisories meant that conditions for the area -- which includes the towns of Pinedale, Boulder, Marbleton and Big Piney -- were forecast to be ideal for ozone levels exceeding the federal healthy standard.
They were the basin's first advisories since February 2009.
"Our forecasters here are doing a great job looking at the whole area and what we might see to create ozone," said department spokesman Keith Guille.
The department said children, the elderly and people with respiratory conditions should limit strenuous or extended outdoor activity.
Heavy drilling has made the Upper Green River Basin one of the nation's top gas producing areas in the last decade or so. The Jonah Field ranked seventh and the Pinedale Anticline field third for 2009 gas production, according to the U.S. Energy Information Administration.
The area had two ozone advisories in 2009 and none last winter. The department issued several in 2008, when drilling peaked before the worst of the recession.
Petroleum companies operating in the Pinedale Anticline said they were taking steps to reduce air pollution during the ozone advisory.
Shell has been telling workers and contractors to postpone nonessential truck trips and to not allow vehicles to idle unnecessarily, company spokeswoman Darci Sinclair said.
The company also is postponing nonessential maintenance that requires bleeding off gas from equipment, she said.
"Just anything we can do that isn't essential in terms of operations or safety," Sinclair said.
Guille didn't speculate on whether industry measures have resulted in less ozone.
"It's kind of hard to tell if it was industry working to reduce those precursors, or if it was certain weather conditions," he said.