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An air quality alert has been issued for Sublette County because of a long standing ozone issue

Pine trees and snow in the foreground, with Pinedale and Fremont Lake in the background.
Caitlin Tan
Wyoming Public Media
Overlooking the town of Pinedale and Fremont Lake.

The Upper Green River Basin has been under an air quality alert for the last couple of days. This comes after 15 years of air quality issues for the area.

The Wyoming Department of Environmental Quality (DEQ) issued an ‘Ozone Action Day’ on Tuesday, March 7, for Sublette County, which means the air quality could be harmful for the elderly, children and those with pre-existing respiratory conditions.

Ground-level ozone is an invisible gas that can be caused by pollutants – like from energy production and cars – that react with sunlight. Notably, the Jonah Field is one of the top producing natural gas fields in the U.S. and is located in Sublette County.

The state has tracked ozone levels in Sublette County since 2005, when the gas industry boomed in the area. Efforts were made in the following years to reduce pollutants and to warn residents of high ozone level days, like retrofitting oil and gas industry equipment to limit emissions and implementing a contingency plan for ‘Ozone Action Days.’ The plan asks the public, including oil and gas operators, to limit idling and refueling trucks and to delay non-essential construction and maintenance activities.

While the average ozone levels did drop in the area between 2011 and 2017, they started to creep up again during the winter of 2017.

“For the last five to six years we haven’t seen those levels up to what we saw in 2011. We’re seeing them again,” said DEQ Spokesman Keith Guille to WPR in 2017. “That prompted the department to issue Ozone Action Days.”

He had pointed out that winter conditions, like sun and limited wind, exacerbate the high ozone issue.

“One of the challenges with wintertime ozone is obviously we can’t control the weather. That being said, the thing we can control the best in our ability as an agency is those emissions,” said Guille.

In 2022, Sublette County received an ‘F’ for ozone pollution from the American Lung Association.

On Sunday, March 5, the max ozone level in the area was 75 parts per billion (ppb)å. The federal health standard is 70 ppb.

The air quality alert expires Tuesday evening, March 7, but March is considered a high ozone month because of the weather conditions, and it is possible to see elevated numbers. On high ozone days, children, elderly and those with respiratory issues should limit time outside.

Caitlin Tan is the Energy and Natural Resources reporter based in Sublette County, Wyoming. Since graduating from the University of Wyoming in 2017, she’s reported on salmon in Alaska, folkways in Appalachia and helped produce 'All Things Considered' in Washington D.C. She formerly co-hosted the podcast ‘Inside Appalachia.' You can typically find her outside in the mountains with her two dogs.
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