BBCMap 2023: Assessing methane emissions from open-cut and underground coal mining in eastern Australia

Methane (CH4) is the second most important anthropogenic greenhouse gas (GHG), and its emissions reduction has been identified as an essential mitigation target to slow down climate change. According to inventories, fossil fuel production and usage account for roughly 17% of the global CH4 emissions, of which approximately 33% originate from coal mining. Accurate identification of coal mining-related CH4 sources and quantification of their annual emission rate is needed for corporate reporting requirements, national inventory verification, and the development of CH4 mitigation strategies. A previous study estimated CH4 emissions for six coal mines in the Bowen Basin in Queensland, Australia, using TROPOMI satellite measurements. It covered a sub-area of the Bowen Basin, where coal is mined at over 40 active mining locations distributed over 60,000 km2. The study showed a significant discrepancy compared to inventory estimates by a factor of 7 during 2018 and 2019. To further verify satellite estimates and improve knowledge of the distribution, persistence, and strength of emissions of this mining region, the Bowen Basin CH4 Mapping (BBCMap) Campaign was conducted in September-October 2023, funded by and performed in collaboration with UNEP's International Methane Emissions Observatory. During this campaign, two HK36 Eco-Dimona research aircraft carrying complementary sensing instrumentation were deployed. The MAMAP2D-Light (Methane Airborne MAPper 2D Light) imaging spectrometer for estimating atmospheric CH4 and CO2 column anomalies and a lidar for topography scans were deployed on one DIMONA HK36 research aircraft, while the second identical aircraft was equipped with an in-situ payload consisting of an LGR OA-ICOS gas analyser for simultaneous measurements of atmospheric CH4, CO2, and water vapor concentrations, a turbulence probe for wind statistics, and a bag sampler for collecting multiple gas samples during each flight for later 13C isotope analyses in the laboratory. This two-aircraft strategy allowed coordinated measurements of CH4 emissions from different coal mines with both remote sensing and in-situ instruments and simultaneous wind measurements, which is essential for deriving a robust flux estimate. During the campaign, 39 flights were conducted, covering approximately 33 mines across roughly 20,000 km2, focussing on the northern part of the Bowen Basin. Preliminary MAMAP2D-Light measurements of atmospheric CH4 column anomalies and emission estimates for both open-cut and underground coal mines will be presented and discussed.