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Methane is a powerful greenhouse gas, and a primary target for mitigatingclimate change in the short-term future due to its relatively short atmosphericlifetime and greater ability to trap heat in Earth's atmosphere compared tocarbon dioxide. Top-down observations of atmospheric methane are possible viadrone and aircraft surveys as well as satellites such as the TROPOsphericMonitoring Instrument (TROPOMI). Recent work has begun to apply the divergencemethod to produce regional methane emission rate estimates. Here we show thatwhen the divergence method is applied to spatially incomplete observations ofmethane, it can result in negatively biased time-averaged regional emissionrates. We show that this effect can be counteracted by adopting a procedure inwhich daily advective fluxes of methane are time-averaged before the divergencemethod is applied. Using such a procedure with TROPOMI methane observations, wecalculate yearly Permian emission rates of 3.1, 2.4 and 2.7 million tonnes peryear for the years 2019 through 2021. We also show that highly-resolved plumesof methane can have negatively biased estimated emission rates by thedivergence method due to the presence of turbulent diffusion in the plume, butthis is unlikely to affect regional methane emission budgets constructed fromTROPOMI observations of methane. The results from this work are expected toprovide useful guidance for future implementations of the divergence method foremission rate estimation from satellite data -- be it for methane or othergaseous species in the atmosphere.

Avoiding methane emission rate underestimates when using the divergence method