How to determine coal mines’ methane emissions

But by applying their new method to New Mexico’s San Juan Basin, the researchers believe it is possible to identify the sources and thus reduce methane emissions.

“We were able to show that individual sources of methane from coal, oil and gas, and fossil fuel infrastructure in the San Juan Basin of New Mexico have different ethane-to-methane ratios that can be detected at different scales, allowing us to distinguish between distinguish them,” Aaron Meyer, lead author of the paper, said in a media statement.

Meyer said the results bring an important new way to map natural gas leaks with greater accuracy, which can help nations meet the Global Methane Pledge signed by the United States, the European Union and about 100 nations at the COP26 climate conference . The pledge aims to reduce global methane emissions by 30% by 2030 compared to 2020 levels.

The San Juan Coal Mine

“Natural gas is primarily methane, but it also contains other hydrocarbons, including ethane,” said Manvendra Dubey, co-author of the article. “The composition of the gas varies depending on the source. We were able to differentiate between these using unique instruments that include many scales used by Los Alamos in the Four Corners. Our findings allow emitters to reduce emissions of methane, which is 84 times more potent as a warming agent than carbon dioxide, this decade.”

The study focused on a methane hotspot discovered several years ago over the Four Corners, and for the first time analyzed observations made on timescales from seconds to hours and length scales from meters to tens of kilometers. The research team carried out measurements using a mobile ground-based measurement system and examined older data from aircraft campaigns and remote sensing platforms.

San Juan Power Plant and Coal Mine
Map showing the San Juan, NM region which contains a large coal mine. Known methane emission sources sampled during the 2020/2021 mobile survey and the location of the Fourier transform spectrometer instrument are identified. (Image from Journal of Geophysical Research: Atmospheres.)

The analysis showed that the vent stack at the San Juan coal mine consistently emitted a stable ethane to methane ratio for eight years of measurements. The ratio held up across a variety of measurement techniques and over a range of distances from the source.

This ethane-to-methane ratio serves as a unique signature that identifies the coal stack and distinguishes it from other sources, many of which had drastically different ratios.

“Despite a diverse and changing emission environment, we have successfully used ethane-to-methane ratios to identify and attribute multiple sources across spatial and temporal scales,” Meyer said. “By using different measurement techniques, we can take advantage of each to build a system-level approach to monitoring an entire tank.”

From the scientist’s point of view, without the possibility of identifying, localizing and quantifying methane emissions, all attempts to reduce them will fail.

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