Removal of Atmospheric Methane by Increasing Hydroxyl Radicals via a Water Vapor Enhancement Strategy

Methane is the second largest contributor to global surface air temperature rise. Reducing atmospheric methane will mitigate climate change and improve air quality. Since the main sink of methane is the hydroxyl radical (OH) in the atmosphere, increasing OH concentration will accelerate the methane oxidation process and reduce methane concentration. Because the primary source of OH is the reaction between water vapor and ozone, scientists have proposed a water vapor enhancement strategy to raise OH concentrations in the atmosphere and remove methane. We use a two-box model to evaluate interactions between OH and methane and a radiative kernel method to calculate radiative responses to water vapor content growth. This proves that increasing OH concentration does have a positive effect on methane reduction. If the concentration of OH is increased by 10% from its current value and maintained for 50 (100) years, 45 Tg yr−1 (67.5 Tg yr−1) more methane will be oxidized by OH, and the cumulative effects of the oxidation are equivalent to a 120.5 Gt (219.6 Gt) reduction in CO2 and will lower the global surface air temperature by 0.054 °C (0.099 °C). Our study also provides insights into a mixed picture of global and regional radiative responses to the growth of water vapor content. The reduced radiative forcing by methane removal cannot overpower the increased radiative forcing by water vapor from the global average point of view. However, due to OH’s greater sensitivity to water vapor and weaker radiative response at higher latitudes, this perspective may be reversed if abrupt CH4 emissions from permafrost thaw occur.