According to an article in the Denver Post, ozone levels in Utah's Uintah Basin, a hotbed of oil and gas drilling, soared in the winter of 2010 and 2011. The 2011 peak was 139 parts per billion (ppb), which is 85% higher than the federal health standard. In the winter of 2005, ozone levels in Pinedale, Wyoming, reached 120 ppb. Pinedale is in the heart of the Green River Basin, and is surrounded by 2,900 gas wells.
Ground-level ozone, which exacerbates asthma and other respiratory ailments, is usually a summertime urban problem. These elevated winter levels exceed New York City's highest reading of 2011, which was 99 ppb.
Brock LeBaron, manager of the Uintah study for the Utah Department of Environmental Quality, told the Denver Post that "What we are seeing in the Uintah Basin and [Wyoming's] upper Green River [Basin] has implications for the entire West." Researchers who looked at the phenomenon in Wyoming speculated that sunlight and heat reflecting off snow can trap the emissions from the oil and gas wells as well as those of vehicles. National Oceanic and Atmospheric Administration scientist Russell Schnell said he suspects the snow acts "as a huge sponge," absorbing chemicals when the temperature drops at night and then releasing them when the sun rises.
The source study can be seen at the Utah Department of Environmental Quality.