Emissions from oil and natural gas operations north of Denver could add to ozone pollution in that region, according to a new study by researchers at the University of Colorado Boulder鈥檚 Cooperative Institute for Research in Environmental Sciences (CIRES).
鈥淎t 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鈥斺�榮tarting ingredients鈥欌�攆or ozone pollution,鈥� said lead author Jessica Gilman, a CIRES research chemist working at the National Oceanic and Atmospheric Administration's Earth System Research Laboratory.
Gilman鈥檚 team found high levels of these VOCs, such as propane, in that area.
鈥淎verage levels of propane were higher than the range of values reported for 28 U.S. cities,鈥� Gilman said. 鈥淔or example, they were four to nine times higher than in Houston, Texas, and Pasadena, California.鈥�
The researchers originally went to the test site, the Boulder Atmospheric Observatory tower about 2.5 miles east of downtown Erie, in winter 2011 to study nighttime air chemistry. 鈥淭he high concentrations of several of the VOCs surprised us,鈥� Gilman said.
To discover the source of the VOCs, Gilman鈥檚 team analyzed more than 550 air samples and determined that oil and natural gas activities were the primary source of those compounds and accounted for 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 was published online in the journal Environmental Science and Technology.
A component of raw natural gas, VOCs such as propane and ethane can leak during extraction, like bubbles escaping from a soda can. VOCs can then react 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鈥檛 initially clear how much of a role oil and gas wells played in the elevated VOC levels.
鈥淲hen our first measurements came out, people would ask, 鈥楬ow do you know the high level of pollutants is from natural gas? How do you know it鈥檚 not from car exhaust, or cattle farms, or people鈥檚 propane grills?鈥欌�� Gilman said. 鈥淏ut we discovered that emissions from oil and natural gas activities have a unique 鈥榗hemical signature鈥� that鈥檚 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.鈥�
The researchers uncovered that signature by analyzing the chemical makeup of all the air samples鈥攃haracterizing 53 different types of VOCs and comparing the results to the composition of raw natural gas.
鈥淓ach source has its own specific composition鈥攃ars look like one thing, trees like another, and so on,鈥� Gilman said. 鈥淛ust like your nose knows what a flower smells like, or coffee, or a farm, our instruments can 鈥榮mell and identify鈥� oil and natural gas emissions. The signature is a very clear, robust marker.鈥�
Once in the air, the VOC emissions can react with sunlight and nitrogen gases to form ground-level ozone pollution. Like wood fuels a campfire, Gilman said, VOCs can fuel the production of ozone pollution.
鈥淲hat this study tells us is how much wood we have piled up there,鈥� she said. 鈥淪o in the wintertime at the BAO tower site, oil and natural gas operations are the dominant source of ozone precursors.鈥�
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 BAO tower respectively, they also detected emissions attributed to oil and natural gas there.
鈥淧ropane and ethane are fairly long-lived in the atmosphere, so they travel far,鈥� Gilman said. 鈥淣o matter where you are in the Front Range, you can still see the signature of VOC emissions from oil and natural gas operations.鈥�
That鈥檚 important since parts of northeastern Colorado marginally exceed EPA standards for ozone pollution.
The researchers next plan to monitor summertime oil and gas emissions, as well as emissions in other states with high oil and gas production, such as Utah.
The results are relevant for people beyond those areas though. 鈥淪ometimes people forget that we all live downwind of somebody,鈥� Gilman said.
Coauthors on the study include CIRES/NOAA scientists Brian Lerner, William Kuster, and Joost de Gouw. The research is funded by NOAA. CIRES is a joint institute of 抖阴旅行射-Boulder and NOAA.
Contact:
Jane Palmer, CIRES science writer, 303-492-6289 (office) or 303-883-4398 (cell)听
Jane.Palmer@colorado.edu听
