Toward Realistic Prognostic Modeling of the Methane Chemical Loss

Global modeling of the hydroxyl radical (OH) remains a significant challenge, pushing chemistry-climate models to rely on idealized scenarios with methane ((Formula presented.)) concentrations rather than emission fluxes. In this study, we employ an emission-driven (Formula presented.) configuration in the Community Earth System Model Version 2.2 (CESM2.2) and demonstrate the effect of incorporating detailed Short-Lived Halogen (SLH) chemistry representation on both emission- and concentration-driven (Formula presented.) simulations in terms of global methane loss and overall chemical dynamics. The net impact of the updated SLH chemistry reduces ozone ((Formula presented.)) and hydroxyl radical (OH) in both hemispheres, resulting in higher abundance and longer lifetime of carbon monoxide (CO) and (Formula presented.). Comparisons with NASA's Atmospheric Tomography (ATom) mission data show joint improvements in OH, (Formula presented.), CO and (Formula presented.). Further evaluation against CO measurements from NASA's Measurement of the Pollution in The Troposphere (MOPITT), (Formula presented.) from JAXA's Greenhouse Gases Observing Satellite (GOSAT) confirms significant amelioration in modeled CO and (Formula presented.), especially in the Northern Hemisphere during winter and spring, correcting a common wintertime underestimation. The annual tropospheric (Formula presented.) loss with OH is reduced from 573 to 504 Tg (Formula presented.) (Formula presented.) in 2017, resulting in an increase in lifetime of about 1.2 years, bringing it to approximately 10 years, which is well within the range of uncertainty in empirical estimates. In contrast, the estimated chlorine sink increases from 2 to around 15 Tg (Formula presented.) (Formula presented.). Additionally, we find that the sensitivity of the (Formula presented.) ’s chemical loss to CO emission changes is underestimated in the prescribed (Formula presented.) simulations.