Tropospheric methane remediation by enhancing chlorine sinks

To tackle global warming, the Paris Agreement (2015) strategically proposed achieving net-zero emissions of greenhouse gases (GHGs) by 2050 and limiting the global temperature rise below 2 °C. This requires a substantial reduction of all GHG emissions across all sectors over the next few decades. Methane has come into the spotlight as the second most potent GHG for its contribution to global warming. The Global Methane Pledge announced at COP26 (2021) proposed to reduce 30% of anthropogenic methane emissions by 2030 compared to the 2020 level. However, studies show that methane emissions will continue to increase even with the planned reductions and therefore the atmospheric methane concentration also. Effective methane removal technologies are urgently required for atmospheric methane remediation. This work evaluates the feasibility of atmospheric methane removal by enhancing the chlorine atom sink (i.e. a natural sink of methane in the lower troposphere) at a significant scale, considering that atomic chlorine initiates methane oxidation 16 times faster than the major natural methane sink of hydroxyl radicals in the atmosphere. Atomic chlorine is proposed to be generated by electrolysis of brine for chlorine gas followed by photolysis. This methane removal technology could be integrated with the state-of-the-art industrial chlor-alkali processes. Such integrated technology is evaluated for the potential of negative GHG emissions and their costs, with attention given to cost-efficient measures, i.e., the use of alternative renewable sources. A brief discussion is included on potential risks, side effects, benefits to the atmospheric methane remediation by 2050 and key required developments.