High wintertime ozone concentrations are relatively new phenomena in rural areas of the West. First observed in 2005 in the oil and gas production areas in the Upper Green River Basin (UGRB) of Wyoming, preliminary studies showed that wintertime ozone levels would spike when snow cover, sunny skies, and strong temperature inversions trapped ozone and its precursor gases near the ground. Emissions from oil and gas operations were implicated as a major source of these e precursors.
During the winter of 2009-10, air quality monitoring showed ozone levels in the Uinta Basin that exceeded air quality standards set by the Environmental Protection Agency (EPA). These high readings raised a number of concerns:
- Effects of High Ozone Levels on the Health of Uinta Basin Residents
- Possible Designation of the Basin as a Nonattainment Area
- Impacts to the Local Economy, Particularly Oil and Gas Operations, from a Nonattainment Designation
Although there have been numerous studies on summertime ozone, less is known about the causes of winter ozone. While summer and winter ozone formation involve the same precursor gases—volatile organic compounds (VOCs) and oxides of nitrogen (NOx)—the atmospheric conditions are different.
Utah State University and DAQ conducted a winter ozone study in 2010-2011 to confirm the presence of these high ozone levels and learn more about the meteorological and climatic conditions associated with elevated ozone concentration. Beginning in the winter of 2011-2012, a collaborative group of county, state, and federal entities, industry organizations, and research organizations launched the multi-year Uinta Basin Ozone Study (UBOS) to gather more information on the causes and possible remedies to wintertime ozone in the Basin.
Support for the multi-year study has come from a variety of partners including the Bureau of Land Management’s (BLM) Utah Office, the Environmental Protection Agency (EPA) Region 8, the National Oceanic and Atmospheric Administration (NOAA), Utah State University, the Uintah Impact Mitigation Special Service District, Western Energy Alliance, Tri-County Health Department, Duchesne and Uintah Counties, and the Ute Indian Tribe.
DAQ partnered with the Utah State University Energy Dynamics Lab to learn more about the extent and behavior of winter ozone development in the Basin. Ten portable air monitors were placed throughout the Basin and neighboring oil and gas fields to measure ozone levels. Five additional monitors were operated by partner agencies and located in other areas of the Basin. Study findings showed areas near Ouray and the central Basin having the highest ozone values while concentrations decreased with distance and increased elevation.
- Episodes Occur Basin-wide
- Highest Ozone Values are Found in the Central Basin
- Ozone Decreases with Increased Elevation
This study was the largest air quality study ever conducted in Utah, with funding coming from a wide range of agencies and partner organizations. While mild wintertime conditions kept ozone standard below federal air quality standards, scientists were still able to collect critical data on the atmospheric chemistry that leads to the formation of winter ozone.
- Snow cover and temperature inversions are key elements of high ozone episodes.
- Oil and gas operations were responsible for 98-99 percent of volatile organic compound (VOC) emissions and 57-61 percent of nitrogen oxide (NOx) emissions.
- Study team’s current best estimate is that VOC controls will reduce ozone, but effectiveness of this strategy is unknown.
- A voluntary “ozone action day” may be a cost effective way to reduce peak ozone concentrations.
Persistent snow cover in 2013 led to inversions, which in turn resulted in ozone concentrations well above the national ambient air quality standards (NAAQS). Individual episodes of elevated ozone ranged from 3 to nearly 15 days in length.
- Reflection of sunlight from the snow surface significantly increases the rate of ozone formation.
- Based on 2012 data, VOC reductions appear to reduce ozone but the overall effectiveness is unknown. The effectiveness of NOx reductions is less certain and under some conditions may increase ozone levels. It is unclearwhether NOx controls become effective when ozone levels are particularlyhigh.
- Unreactive nitrates that recycle into reactive NOx through chemical reactions in snow and on particles in the atmosphere may impact the effectiveness of NOx controls.
- Nitrous acid (HONO) and formaldehyde were found to be the biggest contributors to the creation of the chemically reactive radicals that drive ozone formation.
- Reducing formaldehyde would be an effective way to reduce ozone, but it is not yet clear which sources of formaldehyde are most important.
- Uncertainty in HONO concentrations makes it difficult to predict how responsive ozone will be to reductions in both VOC and NOx emissions.
This study looked at quantifying the contribution of nitrous acid (HONO) and formaldehyde (HCHO) to the chemical reactions responsible for ozone formation. Prior studies in the Basin showed that the radical chemistry that drives ozone production is dominated by HONO and formaldehyde. The final report is due at the end of 2014.
Key preliminary findings
- Nitrous acid (HONO) does not appear to be a major source of radicals during the winter episodes.
- Ozone formation at the Horse Pool study site is sensitive to VOC reductions, and these results also suggest that NOx reductions, either by themselves or in conjunction with VOC reductions, would lead to ozone reductions at Horse Pool. These findings are not sufficiently robust to apply as Basin-wide control strategies, but they provide additional data on possible control options.
- Formaldehyde and other aldehydes are the dominant radical sources in the Basin. Aromatic VOCs, including toluene and xylene, while less abundant than other VOC species in the Basin, are also particularly important sources of radicals.