Demonstration of an Ethane Spectrometer for Methane Source Identification

Abstract

Methane is an important greenhouse gas and tropospheric ozone precursor. Simultaneous observation of ethane with methane can help identify specific methane source types. Aerodyne Ethane-Mini spectrometers, employing recently available mid-infrared distributed feedback tunable diode lasers (DFB-TDL), provide 1 s ethane measurements with sub-ppb precision. In this work, an Ethane-Mini spectrometer has been integrated into two mobile sampling platforms, a ground vehicle and a small airplane, and used to measure ethane/methane enhancement ratios downwind of methane sources. Methane emissions with precisely known sources are shown to have ethane/methane enhancement ratios that differ greatly depending on the source type. Large differences between biogenic and thermogenic sources are observed. Variation within thermogenic sources are detected and tabulated. Methane emitters are classified by their expected ethane content. Categories include the following: biogenic (<0.2%), dry gas (1-6%), wet gas (>6%), pipeline grade natural gas (<15%), and processed natural gas liquids (>30%). Regional scale observations in the Dallas/Fort Worth area of Texas show two distinct ethane/methane enhancement ratios bridged by a transitional region. These results demonstrate the usefulness of continuous and fast ethane measurements in experimental studies of methane emissions, particularly in the oil and natural gas sector.

Contribution of oil and natural gas production to renewed increase in atmospheric methane (2007–2014): top–down estimate from ethane and methane column observations

“…The IHG is calculated from the difference of Zugspitze and Lauder monthly mean time series, assuming that Zugspitze (Lauder) observations are representative of the northern (southern) high-latitude XCH 4 and XC 2 H 6 average. This assumption is supported by the following argumentation: ethane is approximately well-mixed in high northern and southern latitudes (Aydin et al, 2011) as its lifetime of 2.6 months (Xiao et al, 2008) exceeds zonal mixing timescales of about 2 weeks (Williams and Koppmann, 2007). Methane has an even longer lifetime of about 9 years (Prather et al, 2012) and is therefore well-mixed north of 30 • N and in the Southern Hemisphere (Simpson et al, 2002;Saito et al, 2012).…”

“…Major ethane sources are biomass burning, biofuel use, and fossil fuel fugitive emissions from the production and transport of coal (coal-bed gas), oil (associated gas), and natural gas (unassociated gas). About 80 % of global ethane emissions are located in the Northern Hemisphere (Xiao et al, 2008). In contrast to methane, ethane cannot completely mix over both hemispheres, as its lifetime is short compared to the interhemispheric exchange time of approximately 1 year (Tans, 1997;Williams and Koppmann, 2007;Aydin et al, 2011).…”

Methane emissions from natural gas infrastructure and use in the urban region of Boston, Massachusetts

“…Ethane is a significant component of NG, whereas microbial CH 4 sources, such as landfills, sewage, and wetlands, produce little or no C 2 H 6 (15). Because Boston has no geologic CH 4 seeps, no oil and gas production or refining, and low rates of biomass burning, there are no known significant sources of C 2 H 6 in the region other than NG.…”

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

“…McKain et al (2015), for example, measure CH 4 and ethane at several sites in Boston, and they use CH 4 / ethane ratios reported from natural gas pipeline operators to estimate the portion of Boston's CH 4 emissions that are due to natural gas leaks. Several other studies similarly use ethane measurements to explore oil and gas industry emissions from Los Angeles (Wennberg et al, 2012), Dallas, Texas (Yacovitch et al, 2014), the Barnett Shale region Townsend-Small et al, 2015), and from global oil and gas operations (e.g., Simpson et al, 2012;Schwietzke et al, 2014).…”

“…All data in this figure are from the USGS Geochemistry Laboratory Database (USGS Energy Resources Program, 2015). mentation has also become more widely available with Aerodyne, Inc.'s ethane analyzer (Yacovitch et al, 2014).…”