Methane is a powerful greenhouse gas, and a primary target for mitigating climate change in the short-term future due to its relatively short atmospheric lifetime and greater ability to trap heat in Earth's atmosphere compared to carbon dioxide. Top-down observations of atmospheric methane are possible via drone and aircraft surveys as well as satellites such as the TROPOspheric Monitoring Instrument (TROPOMI). Recent work has begun to apply the divergence method to produce regional methane emission rate estimates. Here we show that spatially incomplete observations of methane can produce negatively biased time-averaged regional emission rate estimates via the divergence method, but that this effect can be counteracted by adopting a procedure in which daily advective fluxes of methane are time-averaged before the divergence method is applied. Using such a procedure with TROPOMI methane observations, we calculate yearly Permian emission rates of 3.1, 2.4 and 2.7 million tonnes per year for the years 2019 through 2021. We also show that highly-resolved plumes of methane can have negatively biased estimated emission rates by the divergence method due to the presence of turbulent diffusion in the plume, but this is unlikely to affect regional methane emission budgets constructed from TROPOMI observations of methane. The results from this work are expected to provide useful guidance for future implementations of the divergence method for emission rate estimation from satellite data - be it for methane or other gaseous species in the atmosphere.

翻译：甲烷是一种强效温室气体，且因其在大气中寿命相对较短、相较于二氧化碳对地球大气热捕获能力更强，成为短期应对气候变化的主要靶点。通过无人机和航空测量以及对流层监测仪器（TROPOMI）等卫星平台，可以对大气甲烷进行自上而下的观测。近期研究开始应用散度法生成区域甲烷排放率估算。本文指出，利用散度法对空间不完整的甲烷观测数据进行时间平均时，可能导致区域平均排放率出现负偏差；但通过采用一种新流程——即在对每日甲烷平流通量进行时间平均后再应用散度法——可抵消该效应。基于TROPOMI甲烷观测数据应用该流程，我们计算得出2019年至2021年间二叠纪盆地年排放率分别为310万、240万和270万吨。同时表明，因高分辨率甲烷羽流中存在湍流扩散，散度法对其排放率估算可能产生负偏差，但这种偏差不太可能影响基于TROPOMI甲烷观测构建的区域甲烷排放预算。本研究成果旨在为未来利用卫星数据（无论针对甲烷还是其他大气气态物种）通过散度法估算排放率提供实用指导。