Quantifying Methane Emissions Using Satellite Data: Integrated Methane Inversion (IMI) Model Application for Denmark

After decades of steady growth, even reaching a growth rate of approximately zero from 2000 to 2006, the atmospheric methane (CH₄) has returned to values observed in the second half of the twentieth century, and in recent years it has increased at a faster rate (Palmer et al., 2021). In this context, major initiatives involving the use of satellite-based inversion approaches have been implemented to respond to a growing demand from the climate community. One of this initiatives is the Integrated Methane Inversion (IMI, Varon et al., 2022). IMI is a cloud-based facility developed to infer regional CH₄ emissions at 0.25° × 0.3125° resolution, with dynamic boundary conditions from a global archive of smoothed TROPOspheric Monitoring Instrument (TROPOMI) data. Three monthly IMI simulations were conducted over Denmark to estimate CH₄ emissions before (June 2018), during (June 2020), and after (June 2021) the COVID-19-related lockdowns. The calculated a posteriori emissions for these periods were 0.579 Tg yr^-1, 0.396 Tg yr^-1, and 0.553 Tg yr^-1, respectively. The approximately 31% emission reduction in June 2020 was almost swiftly reversed in June 2021, with a reduction of emissions in June 2021 by less than 5% compared to the same period in 2018. As many months other than June do not frequently meet the IMI preview configuration (a model feature to rate the quality of a proposed inversion without actually performing the inversion), multi-period simulations are being conducted to characterize CH₄ emissions across the country. The new CH₄ emissions data set will serve as a benchmark to evaluate the model performance of the Aarhus University Methane Inversion Algorithm (AUMIA, Vara-Vela et al., 2023). Currently under development, AUMIA is a satellite-based tool designed to quantify CH₄ emissions over Europe, with a specific focus on anthropogenic activities.

References

Palmer, P. L., Feng, L., Lunt, M. F., Parker, R. J., Bosch, H., Lan, X., Lorente, A., and Borsdorff, T.: The added value of satellite observations of methane for understanding the contemporary methane budget, Philos. T. R. Soc. A., 379, 2210, https://doi.org/10.1098/rsta.2021.0106, 2021.

Vara-Vela, A. L., Karoff, C., Benavente, R. N., and Nascimento, J. P.: Implementation of a satellite- based tool for the quantification of CH₄ emissions over Europe (AUMIA v1.0) – Part 1: forward modelling evaluation against near-surface and satellite data, Geosci. Model Dev., 16, 6413-6431, 2023.

Varon, D. J., Jacob, D. J., Sulprizio, M., Estrada, L. A., Downs, W. B., Shen, L., Hancock, S. E., Nesser, H., Qu, Z., Penn, E., Chen, Z., Lu, X., Lorente, A., Tewari, A., and Randles, C. A.: Integrated Methane Inversion (IMI 1.0): a user-friendly, cloud-based facility for inferring high- resolution methane emissions from TROPOMI satellite observations, Geosci. Model Dev., 15, 5787-5805, 2022.