Low Methane Emissions from the Natural Gas Distribution System Indicated by Mobile Measurements in a Chinese Megacity Hangzhou

The consumption of natural gas (NG) in China has quadrupled over the past decade. However, there is an absence of measurement-based assessment of methane emissions from NG consumption, including those from the urban distribution network. Here, we conducted a mobile survey with concurrent measurements of ambient methane concentrations, carbon dioxide concentrations, and 13CH4 isotopic signatures in the center and suburban areas of Hangzhou, a megacity in East China, from November 2021 to June 2022. We detected 176 leak indications in the 1408 km road covered with 32% attributed to NG leaks based on the source isotopic signature and the methane-to-carbon dioxide ratio derived from the Keeling plot and measured concentrations. We quantified the flux using Weller's empirical equation, which yielded an emission factor of 115 L·d–1·km–1 in Hangzhou. The value ranges from 16 to 314 L·d–1·km–1 by accounting for various uncertainty sources. This emission factor falls on the lower end compared to previous studies conducted in North American and European cities. Our findings confirm the effectiveness of mobile surveys in detecting methane emission sources in urban China.