Intercomparison Between Surrogate, Explicit, and Full Treatments of VSL Bromine Chemistry Within the CAM-Chem Chemistry-Climate Model

Many Chemistry-Climate Models (CCMs) include a simplified treatment of brominated very short-lived (VSL^Br) species by assuming CH₃Br as a surrogate for VSL^Br. However, neglecting a comprehensive treatment of VSL^Br in CCMs may yield an unrealistic representation of the associated impacts. Here, we use the Community Atmospheric Model with Chemistry (CAM-Chem) CCM to quantify the tropospheric and stratospheric changes between various VSL^Br chemical approaches with increasing degrees of complexity (i.e., surrogate, explicit, and full). Our CAM-Chem results highlight the improved accuracy achieved by considering a detailed treatment of VSL^Br photochemistry, including sea-salt aerosol dehalogenation and heterogeneous recycling on ice-crystals. Differences between the full and surrogate schemes maximize in the lowermost stratosphere and midlatitude free troposphere, resulting in a latitudinally dependent reduction of ∼1–7 DU in total ozone column and a ∼5%–15% decrease of the OH/HO₂ ratio. We encourage all CCMs to include a complete chemical treatment of VSL^Br in the troposphere and stratosphere.