This problem statement was submitted as part of a research funding application which was awarded by Spark.

Satellite observations are proven for monitoring emission of air pollution and greenhouse gases, supporting policy makers in e.g. the international drive to reduce global methane (CH4) emissions. The capacity to globally map concentrations cannot be matched by other means. E.g., the TROPOspheric Monitoring Instrument (TROPOMI) - one of the currently most advanced satellite instruments for atmospheric composition monitoring – is being used for monitoring emissions like CH4, NO2, CO, HCHO and SO2 from continental scales down to the scale of oil and gas infrastructure (Lauvaux 2022, Veefkind 2023, Dix2023). Besides CH4 emissions reduction, atmospheric CH4 removal approaches can address increasing natural CH4 emissions, as well as anthropogenic CH4 emissions that cannot be mitigated with technology. Suggested potential open-system atmospheric CH4 removal approaches include enhancing oxidizing radicals (Oeste 2017), methanotrophy, and coating surfaces with photocatalysts (Abernethy 2024).

If proven climate-beneficial and cost-effective, open-system approaches, particularly atmospheric oxidation enhancement, likely have the largest potential scale and fastest time to scale (Abernethy 2024). However, open-systems may also be tougher to verify and have higher risks of unintended consequences, and therefore require strong governance approaches. Such governance requires quantification and observations to verify any hypothetical future CH4 removal. For CH4 emission estimates, satellite-based observations have shown to be better suited than local observations (Lauvaux 2022). However, due to technical limitations direct satellite CH4 observations are not available over the oceans, where proposed open-system approaches are envisioned to operate. The research question is how satellite observations from space can quantify CH4 removal, including enhanced CH4 removal due to natural mechanisms such as Cl production by mineral-dust sea spray aerosols (Van Herpen 2023).

If successful, this project will develop a method to observe enhanced atmospheric CH4 oxidation using satellite observations. The most studied approach to enhancing oxidizing radicals in the atmosphere is iron salt aerosols (ISA), in which iron-based particles are lofted into the atmosphere to catalytically generate chlorine radicals that oxidize methane (Oeste 2017). Recently iron salt aerosols have been reported in Sahara dust mixed with sea spray, and it was found to be the dominant source of chlorine in the region, and on the global scale it may increase CH4 loss by an estimated 4.8 Tg y−1 (0.9% of total CH4 loss) (VanHerpen 2023, Röckmann 2024). If successful, this project can help answer research questions about factors that influence chlorine production through this mechanism. The project may also identify world regions where other mechanisms are causing anomalous atmospheric CH4 removal, which could lead to the discovery of new potential approaches for atmospheric CH4 removal.