An Overview of the Bakken Air Quality Study

The Williston Basin covers several hundred thousand square kilometers in parts of North Dakota, Montana, South Dakota, Saskatchewan, and Manitoba.  In the Bakken and Three Forks formations within the Williston Basin, it is estimated that there are more than 7 billion barrels of recoverable oil, making it the largest tight oil play in the United States.  Despite these vast deposits, it is only in the past decade that horizontal drilling and hydraulic fracturing methods have allowed for cost-efficient extraction of these resources, which has led to exponential growth of oil production in the region.  Along with this development has come an increase in associated emissions to the atmosphere.  With emissions from power plants decreasing, new emissions sources related to oil and gas activities are playing an increasingly important role in regional air quality.  Likely tied to these new emissions, haze levels have increased or remained unchanged at some sites in the region since 2000, counter to national trends, and increases in wintertime sulfate and nitrate have been observed.   Concern about potential impacts of oil and gas activities to federal lands in the region prompted the National Park Service to sponsor the Bakken Air Quality Study over two winters in 2013-2014.  Measurements were conducted at five sites: the north and south units of Theodore Roosevelt National Park, Fort Union Trading Post National Historic Site, Knife River National Historic Site, and Medicine Lake National Wildlife Refuge.  Additional data were collected from long-term monitoring networks in the region.  Here we provide an overview of the study and present results aimed at better understanding the impact of local oil and gas emissions on regional air quality.  These analyses are based on measurements of inorganic gases and particles, organic carbon, elemental carbon and volatile organic compounds (VOCs).  Data from the study suggest that while power plants are still an important emissions source in the region, emissions from oil and gas activities are impacting ambient concentrations of nitrogen oxides and black carbon and may dominate recent observed trends in pollutant concentrations at federal lands in the region.  Measurements of VOCs also definitively show that oil and gas emissions were present in almost every air mass sampled over a period of more than four months.