Contact: Jane Palmer, 303-492-6289
Contributed by the NOAA Cooperative Institute for Research in Environmental Sciences at the University of Colorado.
Storage tanks for crude oil (right), condensed natural gas (rear), and waste water (foreground) used in natural gas production on a well pad in northeastern Colorado.
Emissions from oil and natural gas operations north of Denver are releasing gases into the air that could add to ozone pollution in that region, according to a new study by researchers from the NOAA Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado and NOAA.
"At our test site in Weld County, we found that oil and natural gas operations are the dominant wintertime source of certain gases, called volatile organic compounds (VOCs), that act as precursors — starting ingredients — for ozone pollution," said lead author Jessica Gilman, Ph.D., a CIRES research chemist working at NOAA's Earth System Research Laboratory in Boulder, Colo.
Gilman's team found higher-than-expected levels of these gases, such as propane, in that area.
"Levels of propane were four to nine times higher than in large cities with documented air-quality problems, such as Houston or Pasadena," Gilman said.
The researchers originally went to the test site, the Boulder Atmospheric Observatory tower about 20 miles north of Denver, in winter 2011 to study nighttime air chemistry. "The high concentrations of several of the VOCs surprised us," Gilman said.
To discover the source of the gases, Gilman's team analyzed more than 500 air samples, measuring dozens of different VOCs in each of the samples. That level of detail was crucial. It enabled them to determine that oil and natural gas activities were the primary source of those compounds and constituted 55 percent of the hydrocarbons that contribute to ozone formation in this area.
At the time, Weld County had more than 15,000 active oil and gas wells; it currently has about 19,000. The study is now online in the journal Environmental Science and Technology.
A component of raw natural gas, VOCs such as propane and ethane can leak from pipes, valves, storage tanks, and from underground during oil and gas operations. VOCs can then react with other gases in the air to form lung-damaging ozone pollution, a chief component of smog.
Since cars, vegetation, livestock, and other sources also emit VOCs, however, it wasn’t initially clear how much of a role oil and gas wells played in the elevated VOC levels.
"When our first measurements came out, people would ask, "How do you know the high level of pollutants is from natural gas? How do you know it’s not from car exhaust, or cattle farms, or people’s propane grills?' " Gilman said. "But we discovered that emissions from oil and natural gas activities have a unique 'chemical signature that’s very different from emissions from other sources, and it definitively identifies oil and gas wells as the major source of the high levels of VOCs like ethane and propane."
The researchers uncovered that signature by analyzing the chemical makeup of all the air samples—characterizing 53 different types of VOCs and comparing the results to the composition of raw natural gas.
"Each source has its own specific composition — cars look like one thing, trees like another, and so on," Gilman said. "Just like your nose knows what a flower smells like, or coffee, or a farm, our instruments can 'smell and identify' oil and natural gas emissions. The signature is a very clear, robust marker."
Once in the air, the VOC emissions can react with sunlight and other gases (known as nitrogen oxides) to form ground-level ozone pollution. Like wood fuels a campfire, Gilman said, VOCs and nitrogen oxides together fuel the production of ozone pollution.
"What this study tells is us how much wood we have piled up there," she said. "So in the wintertime at the tower site, oil and natural gas operations are the dominant source of ozone precursors."
The oil and gas footprint extends beyond Weld County, though. When the researchers took measurements near Fort Collins and in Boulder, north and west of the Boulder Atmospheric Observatory tower, they also detected emissions attributable to oil and natural gas there.
"Propane and ethane are fairly long-lived in the atmosphere, so they travel far," Gilman said. "No matter where you are in the Front Range, you can still see the signature of VOC emissions from oil and natural gas operations."
That's important since parts of northeastern Colorado marginally exceed the EPA standards for ozone pollution.
The researchers next plan to measure the oil and gas emissions at BAO during summer, the season when other VOC sources such as vegetation and agriculture are likely more prominent, and also the time when ozone pollution is typically higher. They also will be looking at emissions in other states with high oil and gas production, such as Utah.
The results are relevant for people beyond those areas though. "Sometimes people forget that we all live downwind of somebody," Gilman said.
Coauthors on the study include CIRES/NOAA scientists Brian Lerner, William Kuster, and Joost de Gouw. This research was funded by NOAA. CIRES is a joint institute of the University of Colorado Boulder and NOAA.
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