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A new study led by federal scientists is shedding light on the complex photochemical reactions that often push wintertime ozone concentrations in the Uinta Basin over the federal limit.
Data gathered over the past three years shows colder, snowier conditions lead to more ozone formation, according to a paper published Wednesday by the National Oceanic and Atmospheric Administration, or NOAA.
The basin does not have a lot of people and cars, but it is awash in volatile organic compound (VOC) emissions associated with oil and gas drilling, production and processing, researchers found.
"We encountered a range of conditions during the three winters, from snowy in 2013 and 2014, to virtually no snow in 2012," said NOAA's James Roberts, who led the data collection. "Oil and gas emissions of VOCs were high in all three years, but high ozone occurred only in the cold, snowy, stagnant periods."
University of Colorado's Cooperative Institute for Research in Environmental Sciences, or CIRES, collaborated on the study.
The basin's high ozone levels have long puzzled scientists because they occur in the winter, when the sun is low in the sky. Most of the time, ozone levels soar during the summer, in urban areas laced with freeways.
Ozone, a three-atom oxygen molecule, is highly corrosive and can inflame the lungs of those who venture outdoors.
Over the basin town of Ouray, ozone exceeded national air quality standards 49 times during the winter of 2013, according to the study.
In contrast, the summertime air over densely populated Riverside, Calif. east of Los Angeles exceeded the standards, currently set at 75 parts per billion, about half as many times the same year.
According to the U.S. Environmental Protection Agency, oil and gas development is responsible for 97 percent of the VOC emissions in Duchesne and Uintah counties and 62 percent of the nitrogen oxides.
Wintertime inversions often trap cold air near the ground in the basin, concentrating VOCs and other industrial emissions. That ground-level soup helps spur ozone-forming reactions, which are further accelerated by sunlight reflecting off snow cover, the researchers say.
"So it's the same starting ingredients — nitrogen oxides and VOCs — that form ozone in Riverside, but it's a different spark in Utah in winter," said coauthor Steven Brown, a scientist with NOAA's Earth System Research Laboratory in Boulder, Colo. "Under wintertime conditions, the much higher VOCs in Utah break down to make carbonyl compounds, which set off the ozone production."
The Uinta Basin findings are forcing scientists to look at air pollution chemistry differently, according to CIRES researcher Joost de Gouw.
"Our findings could help state and local air quality managers who are faced with ozone episodes to design policies, and industry representatives to meet air quality standards in the regions where they operate." Gouw said.