Methane is a powerful greenhouse gas and is targeted for emissions mitigation by the US state of California and other jurisdictions worldwide1,2. Unique opportunities for mitigation are presented by point-source emitters—surface features or infrastructure components that are typically less than 10 metres in diameter and emit plumes of highly concentrated methane3. However, data on point-source emissions are sparse and typically lack sufficient spatial and temporal resolution to guide their mitigation and to accurately assess their magnitude4. Here we survey more than 272,000 infrastructure elements in California using an airborne imaging spectrometer that can rapidly map methane plumes5,6,7. We conduct five campaigns over several months from 2016 to 2018, spanning the oil and gas, manure-management and waste-management sectors, resulting in the detection, geolocation and quantification of emissions from 564 strong methane point sources. Our remote sensing approach enables the rapid and repeated assessment of large areas at high spatial resolution for a poorly characterized population of methane emitters that often appear intermittently and stochastically. We estimate net methane point-source emissions in California to be 0.618 teragrams per year (95 per cent confidence interval 0.523–0.725), equivalent to 34–46 per cent of the state’s methane inventory8 for 2016. Methane ‘super-emitter’ activity occurs in every sector surveyed, with 10 per cent of point sources contributing roughly 60 per cent of point-source emissions—consistent with a study of the US Four Corners region that had a different sectoral mix9. The largest methane emitters in California are a subset of landfills, which exhibit persistent anomalous activity. Methane point-source emissions in California are dominated by landfills (41 per cent), followed by dairies (26 per cent) and the oil and gas sector (26 per cent). Our data have enabled the identification of the 0.2 per cent of California’s infrastructure that is responsible for these emissions. Sharing these data with collaborating infrastructure operators has led to the mitigation of anomalous methane-emission activity10.
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Radiance and reflectance products calibrated by AVIRIS-NG can be ordered from the AVIRIS-NG data portal at https://avirisng.jpl.nasa.gov/alt_locator/. Retrieved methane images from flight lines in this study are available for download at https://doi.org/10.3334/ORNLDAAC/1727. Vista-CA infrastructure spatial layers are available for download at https://doi.org/10.3334/ORNLDAAC/1726. Images of methane plumes, Vista-CA layers and regional-scale methane-emission products for California can be viewed at https://methane.jpl.nasa.gov/. Tables of methane plume and source characteristics are provided in the Supplementary Information.
The custom computer code or algorithms used to generate the results in this study can be made available to researchers upon request.
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We thank the AVIRIS-NG team and Dynamic Aviation for their efforts in conducting the multiple airborne campaigns involved in this study, and our former colleague at the Jet Propulsion Laboratory (JPL), A. Aubrey, for early support in project planning. We acknowledge G. Franco (California Energy Commission, CEC) and E. Tseng (University of California Los Angeles) for comments on the paper. We appreciate the many discussions and input to flight planning and analysis from our colleagues at the California Air Resources Board (CARB), the Bay Area Air Quality Management District, the South Coast Air Quality Management District, the CEC, Southern California Gas Company, Sunshine Canyon Landfill Local Enforcement Agency, and the Milk Producer’s Council. We thank our colleagues at the Pacific Gas and Electric Company for their support for natural gas control release tests. We thank NASA’s Earth Science Division, particularly J. Kaye, for continued support of AVIRIS-NG methane science. Additional funding for data collection and analysis was provided to JPL by CARB under ARB-NASA Agreement 15RD028 Space Act Agreement 82-19863 and the CEC under CEC-500-15-004. The data from follow-up and contemporaneous Scientific Aviation flights used in this study were funded by CARB. Analysis of this work was also supported in part by NASA’s Carbon Monitoring System (CMS) Prototype Methane Monitoring System for California and the Advancing Collaborative Connections for Earth System Science (ACCESS) Methane Source Finder project. A portion of this research was carried out at the JPL, California Institute of Technology, under contract with NASA (NNN12AA01C). The authors are responsible for the content of the paper and the findings do not represent the views of the funding agencies.
The authors declare no competing interests.
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Duren, R.M., Thorpe, A.K., Foster, K.T. et al. California’s methane super-emitters. Nature 575, 180–184 (2019) doi:10.1038/s41586-019-1720-3