Influence of geographical distribution of VSL oceanic sources and the strength of convection on the tropical bromine partitioning

RAFAEL PEDRO FERNÁNDEZ; ROSS SALAWITCH; DOUGLAS E. KINNISON; JEAN-FRANCOISE LAMARQUE; ALFONSO SAIZ-LOPEZ

Natal

Simposio; 13th Quadrennial ICACGP Symposium & 13th IGAC Science Conference on Atmospheric Chemistry (IGAC-ICACGP-2014); 2014

International Comission on Atmospheric Chemistry and Global Pollution (ICACGP)

Very short-lived (VSL) bromocarbons produced by ocean biology, together with their degradation inorganic products, affect the oxidation capacity of the global atmosphere. The partitioning between the source gas (SG) and product gas (PG) species within the tropical atmosphere affect the total bromine injection to the stratosphere, and depends on the interaction of several processes such as the geographical distribution of sources, the strength of convection and the photochemical lifetime of each species. We present a set of sensitivities studies performed with the CAM-Chem global chemistry-climate model aimed at understanding the contribution of different heterogeneous recycling reactions on the inorganic bromine burden of the marine boundary layer (MBL) and tropical tropopause layer (TTL). A state a state-of-the-art tropospheric and stratospheric halogen chemistry scheme considering physically-based heterogeneous processes over sea-salt aerosols and ice-particles, as well as an individual efficiency of washout/ice-uptake removal for each bromine species, has been used. Our model results suggest that the sea-salt recycling contribution to the active bromine loading of the TTL is only important during periods of strong convection in local regions such as the Western Pacific warm pool, being negligible on a tropical annual average. Also, the occurrence of the ice-mediated recycling reactions strongly affects the total bromine loading of the TTL, affecting the strength of stratospheric injection. Globally, we modeled the tropical annual average stratospheric bromine injection due to VSL sources to be 5 pptv, with the inorganic contribution (PG ~3 pptv) surpassing the carbon-bonded portion (SG ~2 pptv). This implies that the larger portion of PGVSL injection is already in its active form in the lower stratosphere, where the ozone depleting potential of bromine is maximized.