SUBLETTE COUNTY – Snow will blanket the Upper Green River Basin’s sagebrush flats in the near future, and on sunny days with temperature inversions, the potential for increased, unhealthy levels of winter ozone will rise with more gas and oilfield pollutants trapped at ground level.
Last winter, the Upper Green River Basin’s unusual winter ozone levels exceeded the federal standard of 70 parts per billion for eight hours, leading to seven “ozone action days” as designated by the Wyoming Department of Environmental Quality.
The first known winter ozone exceedances were recorded here in 2005, when the federal standard had been 84 ppb since 1997. The Environmental Protection Agency lowered that to 75 ppb in 2008 and revised it to 70 ppb in 2015.
Since 2005, scientists identified four factors that when combined could lead to ozone exceedances – mainly high “precursor” levels of nitrogen oxides (NOx) and volatile organic compounds (VOCs) or polluting chemicals that “bake” in bright sunlight reflected from unbroken snow cover with temperature inversions and low winds present.
Resulting high levels of ozone can cause or aggravate respiratory problems in the young, old and people active outdoors. The Wyoming Department of Health has noted increased problems reported after OADs.
After years without UGRB exceedances and lower gas and oilfield activity, the 2017 ozone action days were unexpected.
Last May 3, Air Quality Division Administrator Nancy Vehr took comments at the UGRB post-season ozone meeting. One was