An oil and natural gas field in the western United States is largely responsible for a global uptick of the air pollutant ethane, according to a new study.
The team led by researchers at the University of Michigan found that fossil fuel production at the Bakken Formation in North Dakota and Montana is emitting roughly 2 percent of the ethane detected in the Earth's atmosphere.
Along with its chemical cousin methane, ethane is a hydrocarbon that is a significant component of natural gas. Once in the atmosphere, ethane reacts with sunlight to form ozone, which can trigger asthma attacks and other respiratory problems, especially in children and the elderly. Ethane pollution can also harm agricultural crops. Ozone also ranks as the third-largest contributor to human-caused global warming after carbon dioxide and methane.
The study was launched after a mountaintop sensor in the European Alps began registering surprising spikes in ethane concentrations in the atmosphere starting in 2010, following decades of declines. The increase, which has continued over the last five years, was noted at the same time new horizontal drilling and hydraulic fracturing techniques were fueling a boom of oil and gas production from previously inaccessible shale rock formations in the United States.
Searching for the source of the ethane, an aircraft from the National Oceanic and Atmospheric Administration in 2014 sampled air from directly overhead and downwind of drilling rigs in the Bakken region. Those measurements showed ethane emissions far higher than what was being reported to the government by oil and gas companies.
"These findings not only solve an atmospheric mystery — where that extra ethane was coming from — they also help us understand how regional activities sometimes have global impacts," said Colm Sweeney, a study co-author from the Cooperative Institute for Research in Environmental Sciences at the University of Colorado in Boulder. "We did not expect a single oil field to affect global levels of this gas."
The researchers said other U.S. oil and gas fields, especially the Eagle Ford in Texas, are also likely contributing to the global rise in ethane concentrations. Ethane gets into the air through leaks from drilling rigs, gas storage facilities and pipelines, as well as from intentional venting and gas burnoffs from extraction operations.
Regulators at the Environmental Protection Agency are reviewing the results of the new study. Spokeswoman Laura Allen said Friday that new clean air rules recently announced by the Obama Administration to curb climate-warming methane leaks from oil and gas drilling operations should also help address the harmful ethane emissions.