Potential Air Quality Side-Effects of Emitting HO to Enhance Methane Oxidation as a Climate Solution.

Methane (CH) is a greenhouse gas with a global warming potential 81.2 times higher than carbon dioxide (CO). The intentional emission of oxidants into the atmosphere has been proposed as a geoengineering solution to accelerate the oxidation of CH to CO, thereby reducing surface warming. However, there has been little consideration for competing atmospheric oxidation pathways that will reduce CH oxidation efficiencies and result in the formation of secondary pollutants such as ozone and particulate matter. Using a global chemical-transport model, we simulate a proposed technology to intentionally emit HO into the atmosphere to elevate OH concentrations and enhance CH oxidation. We find that proposed emission rates of oxidants have minimal impacts on monthly average tropospheric ozone and particulate matter concentrations. However, competition for the oxidation of CH would necessitate widespread adoption of such technology to remove substantial concentrations of atmospheric CH, which would in-turn cause considerable increases in regional winter-time particulate matter. Our work underscores the need to consider competing chemistry in evaluating the efficacy and side effects of proposals to enhance the atmospheric oxidation of CH as a climate solution.