Role of Future Climate Change, Air Pollution Control and Methane Mitigation in Driving Hydroxyl Radical (OH) and Methane Lifetime

Abstract The hydroxyl radical (OH) determines the atmospheric lifetime of many pollutants like methane (). This study isolates climate change, air pollution control and mitigation effects on OH concentrations ([OH]) and lifetime, by analyzing Coupled Model Intercomparison Project Phase 6 (CMIP6) Aerosol Chemistry Model Intercomparison Project (AerChemMIP) multi‐model outputs for variants of the high‐emission SSP3‐7.0 scenario. Models agree that warming increases [OH] and decreases lifetime, leading to a multi‐model mean radiative forcing reduction of −0.038 . However, the overall trend in SSP3‐7.0 is decreasing [OH] and increasing lifetime, confirming that changes in and other short‐lived climate forcers (SLCFs)) dominate over climate‐related drivers. Meanwhile, air pollution controls, if not paired with reduction, can reduce [OH] and lengthen lifetime, potentially undermining climate efforts. In a cleaner‐air future, mitigation will be essential to sustain higher [OH], shorten lifetime, and reduce its radiative forcing.