## 4 Results
### High-Frequency Monitoring of Methane Point Sources
#### 4.2.2 EOG Shale Gas Well in Eddy County, New Mexico  
Utilizing the Sentinel-2 platform on GEE, we conducted high-frequency monitoring of two methane point sources: the Sanyuan Nan Yao Coal Mine in Shanxi and the EOG Shale Gas Well in Eddy County. The EOG Shale Gas Well was initially detected by GF5-02-AHSI in February 2022, with its scale later confirmed by TROPOMI [42]. The location is depicted in the lower right corner of Figure 9. The New Mexico source is a piece of equipment from a shale gas well.  
From 1 January 2020 to 30 August 2024, out of 293 Sentinel-2 satellite overpasses, we identified 64 detectable methane plumes from the EOG Shale Gas Well point source, averaging 1 overpass every 5.9 days. Among the 293 detected instances, 79 were due to cloud cover, and 149 showed no detectable plumes, indicating a plume persistence rate of 29% in the cloud-free observations. The lack of detection could be due to the source being inactive or emissions falling below the Sentinel-2 detection threshold. For each cloud-free scenario, we determined plume detection by employing the MBMP retrieval method within a 1 \(\times\) 1 km\({}^{2}\) area centered on the point source. We constructed methane plume masks and estimated the source emission rates using the MBMP retrieval method, as shown in Figure 9, which displays some of the methane plumes retrieved from the EOG Shale Gas Well point source. The emission rates and quantities from the methane point source appeared to be unrelated to the season. Out of 64 plume detections, we estimated the emission rates for 62, disregarding 2 instances that were difficult to distinguish from methane plumes during the retrieval process. Figure 10 illustrates the time series results of source emission  
Figure 8: The point source of the Sanyuan Nan Yao Coal Mine in Shanxi, and the MBMP retrievals according to Sentinel-2 observations.  
rates, ranging from 2.1 to 22.9 t/h, with an average standard deviation of 7.3 \(\pm\) 3.5 t/h. In September 2022, we observed a significant reduction in emissions from this methane point source, possibly due to control measures taken by the facility operator. Assuming a 29% persistence rate without daily variations, our estimate of the average emission rate implies a total of 16,000 tons of methane emitted over a year-long emission event. This represents 0.9% of the 17 million tons of national methane emissions reported by the U.S. government to the United Nations Framework Convention on Climate Change for the oil and gas industry in 2023. Given the intervention by the facility operator in September 2022, it seems that a significant portion of these emissions could have been avoided if the operator had been notified shortly after the emissions began. Sentinel-2 imagery could enable such interventions in the future.  
Figure 10: The EOG Shale Gas Well point source in Eddy County, and use of the MBMP retrievals according to Sentinel-2 observations.  
Figure 9: Methane plume masks detected at methane point sources located in the EOG Shale Gas Well in Eddy County, New Mexico, according to Sentinel-2 observations, with red circles indicating the emission sources, and the image in the second row, fifth column showing the located emission source. The white arrow indicates the direction of the wind, the background is from ©Google Earth imagery. The dates in the figure are (**a**) 31 December 2023; (**b**) 9 November 2023; (**c**) 10 September 2023; (**d**) 1 August 2023; (**e**) 24 June 2023; (**f**) 7 May 2023; (**g**) 9 May 2023; (**h**) 8 February 2023; (**i**) 7 December 2022.