Investigating the Role of Short-Lived Halogen Chemistry and Chemical Feedback on CH₄-CO-OH Distributions Using Emission-Driven CESM/CAM-Chem Simulations
Mohammad Amin Mirrezaei1, Benjamin Gaubert2, Ivan Ortega2, Kathryn McCain3, Lori Bruhwiler3, Youmi Oh3,4, Alfonso Saiz-Lopez5, Raphael Fernandez6,7, Avelino F. Arellano Jr1
1Department of Hydrology and Atmospheric Sciences, University of Arizona, AZ, USA
2Atmospheric Chemistry Observations & Modeling Laboratory (ACOM), NSF National Center for Atmospheric Research (NSF NCAR), Boulder, CO, USA
3Global Monitoring Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO, USA
4Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, CO, USA
5Department of Atmospheric Chemistry and Climate, Institute of Physical Chemistry Blas Cabrera, CSIC, Madrid, Spain
6Institute for Interdisciplinary Science, National Research Council (ICB-CONICET), Mendoza, Argentina
7School of Natural Sciences, National University of Cuyo (FCEN-UNCuyo), Mendoza, Argentina
Understanding the global methane (CH4) budget is essential for accurately interpreting observed variations in atmospheric CH₄ concentrations. However, uncertainties in hydroxyl radical (OH) trends and CH4 flux estimates complicate efforts to quantify CH4 sources and sinks. Global chemistry climate models serve as a primary tool for linking CH4 emissions to atmospheric levels, but they often struggle with estimating CH4 lifetime due to uncertainties in oxidation processes and emissions. To improve these estimates, we conduct a series of chemistry-climate simulations using CESM/CAM-Chem, incorporating multiple CH4 flux estimates from the Global Carbon Project and NOAA Carbon Tracker. These simulations span 2014 to 2018 and include both standard MOZARTTS1.2 chemistry and an interactive representation of very short-lived halogens. The modeled distributions of CH4 and CO are evaluated against observations from satellite retrievals (GOSAT, MOPITT), ground-based solar infrared measurements (NDACC), and aircraft-based profiles from the Atmospheric Tomography Mission (ATom) over major ocean basins. Our results demonstrate that interactive, emission-driven simulations improve CH4 loss estimates by approximately 15% due to OH suppression from short-lived halogen interactions with ozone (O3). This approach also enhances the representation of tropospheric O3 and CO, leading to better agreement with observational datasets.