15 August 2016 (NASA) – In an extensive airborne survey, a NASA-led team has analyzed a previously identified "hot spot" of methane emissions in the Four Corners region of the United States, quantifying both its overall magnitude and the magnitudes of its sources. The study finds that just 10 percent of the individual methane sources are contributing half of the emissions.
Scientists from NASA's Jet Propulsion Laboratory and Caltech, both in Pasadena, California; the National Oceanic and Atmospheric Administration (NOAA), Boulder, Colorado; and the University of Michigan, Ann Arbor, used two JPL airborne spectrometers to identify and measure more than 250 individual sources of methane. The sources emitted the gas at rates ranging from a few pounds to 11,000 pounds (5,000 kilograms) per hour. Results are published this week in the Proceedings of the National Academy of Sciences in a paper titled "Airborne methane remote measurements reveal heavy-tail flux distribution in Four Corners region." Christian Frankenberg of JPL and Caltech is the lead author.
As a greenhouse gas, methane is very efficient at trapping heat in Earth’s atmosphere, contributing to global warming. In the Four Corners region, where Arizona, Colorado, New Mexico, and Utah meet, methane emissions are primarily associated with the production and transport of natural gas from coal beds. The odorless, colorless gas is difficult to detect without scientific instruments.
The experiment was a proof of concept for airborne detection of methane, according to Frankenberg. "That we could observe this distribution in a widespread geographical area and collect enough plumes to perform a statistical analysis was a pleasant surprise," he said.
A group of researchers including Frankenberg originally detected the Four Corners methane hot spot using past observations from a European satellite. Last year, he and JPL colleagues joined a campaign, led and funded by NOAA, to investigate the hot spot, called Twin Otter Projects Defining Oil/gas Well emissioNs (TOPDOWN). The campaign also included researchers from the University of Michigan. Each participating institution deployed its own suite of instruments.
The NASA spectrometers used in the study can identify certain atmospheric gases, including methane, by the way the gases absorb sunlight. NOAA provided airborne plume measurements that were used to calibrate and validate the NASA data.
NASA collects data from space, air, land and sea to increase our understanding of our home planet, improve lives and safeguard our future. NASA develops new ways to observe and study Earth's interconnected natural systems with long-term data records. The agency freely shares this unique knowledge and works with institutions around the world to gain new insights into how our planet is changing.
ABSTRACT: Methane (CH4) impacts climate as the second strongest anthropogenic greenhouse gas and air quality by influencing tropospheric ozone levels. Space-based observations have identified the Four Corners region in the Southwest United States as an area of large CH4 enhancements. We conducted an airborne campaign in Four Corners during April 2015 with the next-generation Airborne Visible/Infrared Imaging Spectrometer (near-infrared) and Hyperspectral Thermal Emission Spectrometer (thermal infrared) imaging spectrometers to better understand the source of methane by measuring methane plumes at 1- to 3-m spatial resolution. Our analysis detected more than 250 individual methane plumes from fossil fuel harvesting, processing, and distributing infrastructures, spanning an emission range from the detection limit ∼ 2 kg/h to 5 kg/h through ∼ 5,000 kg/h. Observed sources include gas processing facilities, storage tanks, pipeline leaks, and well pads, as well as a coal mine venting shaft. Overall, plume enhancements and inferred fluxes follow a lognormal distribution, with the top 10% emitters contributing 49 to 66% to the inferred total point source flux of 0.23 Tg/y to 0.39 Tg/y. With the observed confirmation of a lognormal emission distribution, this airborne observing strategy and its ability to locate previously unknown point sources in real time provides an efficient and effective method to identify and mitigate major emissions contributors over a wide geographic area. With improved instrumentation, this capability scales to spaceborne applications [Thompson DR, et al. (2016) Geophys Res Lett 43(12):6571–6578]. Further illustration of this potential is demonstrated with two detected, confirmed, and repaired pipeline leaks during the campaign.
SIGNIFICANCE: Fugitive methane emissions are thought to often exhibit a heavy-tail distribution (more high-emission sources than expected in a normal distribution), and thus efficient mitigation is possible if we locate the strongest emitters. Here we demonstrate airborne remote measurements of methane plumes at 1- to 3-m ground resolution over the Four Corners region. We identified more than 250 point sources, whose emissions followed a lognormal distribution, a heavy-tail characteristic. The top 10% of emitters explain about half of the total observed point source contribution and ∼1/4 the total basin emissions. This work demonstrates the capability of real-time airborne imaging spectroscopy to perform detection and categorization of methane point sources in extended geographical areas with immediate input for emissions abatement.