Natural Gas Leakage Ratio Determined from Flux Measurements of Methane in Urban Beijing

A limited understanding of urban methane (CH4) emissions in China challenges the evaluation of the coal-to-gas switch toward carbon neutrality by 2060. CH4 flux was measured in urban Beijing using the eddy covariance method during a summer campaign. With a mean of 152.6 ± 107.9 nmol/m2/s, the CH4 flux was estimated to depend little on the intensity of human activities, with minimal influence from biogenic sources. Emission hotspots with large temporal variability were identified in the study fetch area, which increased the mean CH4 flux by 12.5%. Based on the lack of large, known biogenic sources in nonhotspot (background) areas, we attributed the CH4 flux in these areas (135.6 ± 70.56 nmol/m2/s) mainly to natural gas. Thus, we estimate as an upper limit that natural gas contributes 88.9% to the total CH4 flux in urban Beijing. However, poor alignment between the dominant sources in the inventories and the characteristics of the measured CH4 flux were observed, suggesting substantial underestimation of emissions from natural gas sources in the inventories. A leakage ratio of 1.4% (0.7–2.1%) of consumed natural gas was determined in Beijing. Pinpointing emissions with more granular methods could improve our understanding of the urban CH4 source profile in Beijing.