Kavli Affiliate: Kaisey Mandel
| First 5 Authors: Clayton Roberts, Rutger IJzermans, David Randell, Matthew Jones, Philip Jonathan
| Summary:
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
when the divergence method is applied to spatially incomplete observations of
methane, it can result in negatively biased time-averaged regional emission
rates. We show 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.
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