Airborne methane remote measurements reveal heavy-tail flux distribution in Four Corners region

Abstract

Methane (CH 4 ) 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 CH 4 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)

Mobile measurement of methane emissions from natural gas developments in northeastern British Columbia, Canada

“…According to a distribution of emissions at a US oil and gas site in the Four Corners region, emissions < 0.2 g s −1 did not significantly contribute to the overall CH 4 flux rate (Frankenberg et al, 2016). If the US study by Frankenberg et al (2016) reflects the emission patterns in the Montney, then our mobile method was able to capture the most significant emission sources in the area. By applying calculated emission rates to the fraction of infrastructure we found to be persistently emitting, we estimated the total volume of CH 4 being released annually from sites emitting at rates above our MDL.…”

“…Using MDLs for our study, we can reasonably estimate the minimum likely emissions inventory, because it is expected that infrastructural sources with larger emission rates cumulatively contribute the majority of CH 4 emissions (Frankenberg et al, 2016;Mitchell et al, 2015;Rella et al, 2015;Subramanian et al, 2015;Zavala-Araiza et al, 2015). According to a distribution of emissions at a US oil and gas site in the Four Corners region, emissions < 0.2 g s −1 did not significantly contribute to the overall CH 4 flux rate (Frankenberg et al, 2016).…”

“…Following the dilution experiments, we used the NOAA Air Resources Laboratory Gaussian Dispersion Model (Draxler, 1981) to determine the minimum CH 4 release rate that our mobile method distinguished from ambient at our various plume detection distances (minimum detection distance was 11 m, maximum was 496 m). One main assumption in the model is that the emission release occurred 1 m above ground level, but it is likely that we encountered varying emission source heights, particularly between wells and facilities.…”

“…Detection of atmospheric fugitive emissions from upstream sources has previously been attempted with top-down methods and specific ground-based techniques. Top-down measurements include airborne (Karion et al, 2013;Caulton et al, 2014) and remote sensing (Govindan et al, 2011;Schneising et al, 2014) measurements. These methods often cover large areas in low resolution, making it difficult to identify exact sources of emissions.…”

Constraining sector-specific CO&lt;sub&gt;2&lt;/sub&gt; and CH&lt;sub&gt;4&lt;/sub&gt; emissions in the US

“…2). In addition to these urban and oil and gas studies, Lindenmaier et al (2014) and Frankenberg et al (2016) use spectroscopic CO 2 and CH 4 observations, respectively, to identify emissions from resource extraction in the Four Corners region of the western US. The observational strategies described above are relatively diverse.…”