Study of spatiotemporal variation and annual emission of CH in Shaoxing Yangtze River Delta, China, Using a portable CH detector on the UAV.

Methane (CH) is the second greenhouse gas and has a profound impact on global climate change due to its high global warming potential and concentration. By 2022, the CH concentration was approximately 1.9 ppm, which was 264% of the pre-industrial level. The spatiotemporal distribution of CH was investigated by a portable CH detector on an unmanned aerial vehicle and electric bicycles in Shaoxing, a city situated in the Yangtze River Delta, China. The vertical distribution revealed CH concentration generally decreased slowly with height. However, the inversion condition and low atmospheric boundary layer height (ABLH) leaded to the enhancement of CH with height. The highest CH concentration (2.2 ± 0.1 ppm, n = 1428) was observed in winter and the lowest (2.0 ± 0.2 ppm, n = 1530) in spring. Regarding the daily variation, CH concentration peaked at 5:00 local time (LT) and reached its lowest level at 14:00 LT, which was attributed to the daily variation of ABLH, lowest in the early morning and highest in the noon. In urban areas, CH concentrations showed higher levels near restaurants, natural gas stations and sewerage well, with a maximum value of 13.1 ppm, which was caused by CH emission and natural gas leakage from these places. The annual CH emission in Shaoxing were estimated to be approximately 69 ton/(km·year) by the mass balance approach. Compared with other cities in the world, the CH emission is in higher level which imply some control measures should be conducted to reduce CH emission in Shaoxing.