Mitigation of atmospheric and elevated methane by photochemical oxidation at ambient conditions

Methane (CH₄) is a potent greenhouse gas and increased mitigation of anthropogenic sources will have immediate effects on global climate. Methane is an inherently inert gas and there is a need for methods capable of mitigating methane from point and non-point sources. Here we introduce a UV based methane oxidation system for mitigation of methane at atmospheric levels and above. Catalyst-free photochemical methane oxidation was achieved at ambient temperature and pressure using air and water vapor as sole reactants. Products included H₂, H₂O, CH₂O and CO₂ that have lower radiative forcing potential than methane. The oxidation process rapidly removed ambient methane (2 ppm) to well below atmospheric levels within seconds. >90 % methane removal was obtained for both atmospheric and elevated methane (1-100,000 ppm). Rate coefficients increased with decreasing methane concentrations with half-life of <1 min to 10 min for concentrations ≤10,000 ppm. The environmental applicability of the process for mitigation of anthropogenic methane was demonstrated with thermogenic methane from a gas distribution hub and biogenic methane from a pig stable. The study introduces the fundamentals of a methane scrubber based on rainwater and UV irradiation that may contribute to future removal of methane from point and non-point sources.