地球メタン宣言を達成するための鍵となる、より良い発生源の特定を可能にする複数の観測形態。 Multiple forms of observation allow better source attribution, key to meeting the Global Methane Pledge
2022-10-05 アメリカ・ロスアラモス国立研究所(LANL)
この結果は天然ガスの漏洩をより忠実に特定するための重要な新機能をもたらし、COP26気候変動会議で米国、欧州連合、約100カ国が署名した「グローバルメタン公約」を各国が達成するのに役立つという。この公約は、2030年までに世界のメタン排出量を2020年比で30％削減することを目標としている。
この発見は、二酸化炭素の84倍もの温暖化物質であるメタンの排出を、この10年間で削減するために、排出者の説明責任を果たすことを可能にする。
研究チームは、移動式の地上観測システムで測定し、航空機によるキャンペーンやリモートセンシングプラットフォームによる古いデータを調査した。その結果、サンファン炭鉱のベントシャフトからは、8年間にわたり一貫して安定したエタンとメタンの比率が放出されていることが分かった。この比率は、さまざまな測定方法と発生源からのさまざまな距離で維持された。
このエタンとメタンの比率は、炭鉱の噴出孔を特定し、比率が大きく異なる他の噴出孔と区別するための明確なサインになる。
エタン-メタン比を使用して、空間と時間のスケールでいくつかの排出源を特定し、分類することに成功した。
＜関連情報＞
- https://discover.lanl.gov/news/1004-natural-gas-emitters
- https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022JD037092
マルチスケールエタン/メタン観測による2013年から2021年までのサンフアン盆地における炭鉱排気の属性分析 Using Multiscale Ethane/Methane Observations to Attribute Coal Mine Vent Emissions in the San Juan Basin From 2013 to 2021
Aaron G. Meyer,Rodica Lindenmaier,Sajjan Heerah,Katherine B. Benedict,Eric A. Kort,Jeff Peischl,Manvendra K. Dubey
Journal of Geophysical Research: Atmospheres Published: 09 September 2022
DOI:https://doi.org/10.1029/2022JD037092
Abstract
Source attribution of natural gas emissions from fossil fuels in New Mexico’s San Juan Basin (SJB) is challenging due to source heterogeneity and emissions transience. We demonstrate that ethane (C2H6) to methane (CH4) mixing ratios can identify and separate sources over different scales using various measurement techniques. We report simultaneous CH4 and C2H6 observations near a coal mine vent and oil and gas (O&G) emission sources using ground-based in situ measurements in 2020/2021. During these campaigns, we observed a stable coal vent C2H6:CH4 ratio of 1.28% ± 0.11%, discernibly different than nearby O&G source ratios ranging from 0.9% to 16.8%. We analyze airborne observations of the SJB taken in 2014/2015 that exhibit similar coal vent ratios and further show the region’s heterogeneity. We identify episodic O&G sources, including a gas plant source detected in 2014/2015 that is absent in our 2020/2021 data. We examine total column observations of C2H6 and CH4 made in 2013 with a solar spectrometer and find a C2H6:CH4 ratio of 1.3% ± 0.4% for the coal vent. The stable and unique coal vent ratio relative to other O&G sources in the region is used to demonstrate that consistent attribution is possible using various measurement methods at multiple scales across many years. Finally, we demonstrate that using C2H6 as a proxy for fossil CH4 inversions can inform detailed basin-scale inversions, provided we understand source specific changes in the C2H6:CH4 ratio like we report in the SJB.
Key Points
- Multiple measurement techniques across spatiotemporal scales show consistent and stable ethane:methane ratios from a coal vent shaft
- Ethane:methane ratios are a valuable tool for source apportionment, plume separation, and oil and gas basin emissions characterization
- A large gas plant source was identified in 2015 but abated in 2021 showing change with time and monitoring
Plain Language Summary
Oil, gas, and coal production processes are known to emit methane, a potent greenhouse gas, and other hydrocarbon air pollutants. Attributing these emissions to specific anthropogenic fossil sources is challenging in the vast and variable infrastructure. Ethane is often co-emitted with methane and the ratio of ethane to methane in emission sources varies significantly with source types. By measuring this ratio with high sensitivity and accuracy, we can “fingerprint” gas sources by their unique ratio. We report simultaneous measurements of ethane and methane, and an empirical analysis of the ratio to demonstrate source specific attribution. Our varied measurement techniques spanning spatial scales (near-source ground, airborne, and remote sensing) were used to sample sources in New Mexico’s San Juan basin over 8 years. Despite a diverse and changing emissions environment, ethane to methane ratios were successfully used to identify and apportion several sources across scales in space and time. Specifically, our measurements show consistent and stable ethane to methane ratios from a large coal vent source in the study region. Our findings inform efforts seeking to characterize and quantify gas emissions in fossil extraction regions using multi-scale data from diverse instruments.
