Impact of Halogen Chemistry on CH4-CO-OH Distribution in Emission Driven CAM-Chem Simulations

As nations seek to develop strategies to manage their carbon emissions, capabilities of quantifying, verifying, monitoring, and reporting local-to-global carbon sources and sinks (or budget) are necessary for informed policy decisions. Attributing methane (CH₄) sources is exacerbated by its strong coupling with atmospheric chemistry via its loss to hydroxyl radical (OH) reaction, which is the main oxidizing agent in our atmosphere. While attention has been focused on estimating the sources of atmospheric CH₄ based on available surface and recent satellite observational constraints of CH₄, the uncertainties in atmospheric CH₄ sink estimates remain significant. The most recent halogen chemical scheme strongly impacts the CH₄ lifetime and could be key in reconciling the CH4 budget estimates, including its isotopic fractionation trend. We run the Community Atmosphere Model with chemistry (CAM-chem) with posterior CH₄ emission fluxes from the Global Carbon Project and the Carbon Tracker CH₄. We contrast simulations with standard chemistry and with the recently updated and detailed treatment of halogen chemistry.

We will focus the evaluation on the inter-annual and seasonal cycle variability and on the longitudinal gradients of CH₄ and CO as observed by NOAA Global Greenhouse Gas Reference Network, the international Network for the Detection of Atmospheric Composition Change (NDACC). We also compare the simulated abundance and lifetime of CH4 and its related chemical constituents (CO, O₃, OH) with measurements from NASA Airborne Atmospheric Tomography Mission (ATom) and the NSF O₂/N₂ ratio and CO₂ airborne Southern Ocean study.