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

Abstract

Many Chemistry‐Climate Models (CCMs) include a simplified treatment of brominated very short‐lived (VSL ^Br) species by assuming CH ₃Br 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/HO ₂ ratio. We encourage all CCMs to include a complete chemical treatment of VSL ^Br in the troposphere and stratosphere.

Key Points

• Using CH ₃Br as surrogate for brominated very short‐lived (VSL ^Br) species reproduces upper stratosphere bromine, but the impact on lowermost stratospheric ozone is underestimated

• An explicit approach for CHBr ₃ and CH ₂Br ₂ captures the expected bromine stratospheric injection but underestimates tropospheric impacts

• Only the full chemical treatment of VSL ^Br sources results in a coherent bromine representation in the troposphere and lowermost stratosphere