Articles | Volume 14, issue 24
Atmos. Chem. Phys., 14, 13391–13410, 2014
Atmos. Chem. Phys., 14, 13391–13410, 2014

Research article 16 Dec 2014

Research article | 16 Dec 2014

Bromine partitioning in the tropical tropopause layer: implications for stratospheric injection

R. P. Fernandez1, R. J. Salawitch2, D. E. Kinnison3, J.-F. Lamarque3, and A. Saiz-Lopez1 R. P. Fernandez et al.
  • 1Atmospheric Chemistry and Climate Group, Institute of Physical Chemistry Rocasolano, CSIC, Madrid 28006, Spain
  • 2Department of Atmospheric and Oceanic Science, Department of Chemistry and Biochemistry, and Earth System Science Interdisciplinary Center, University of Maryland, College Park, Maryland, MD 20742, USA
  • 3Atmospheric Chemistry Division, NCAR, Boulder, CO 80301, USA

Abstract. Very short-lived (VSL) bromocarbons are produced at a prodigious rate by ocean biology and these source compounds (SGVSL), together with their inorganic degradation products (PGVSL), are lofted by vigorous convection to the tropical tropopause layer (TTL). Using a state-of-the-art photochemical mechanism within a global model, we calculate annual average stratospheric injection of total bromine due to VSL sources to be 5 pptv (parts per trillion by volume), with ~ 3 pptv entering the stratosphere as PGVSL and ~ 2 pptv as SGVSL. The geographic distribution and partitioning of VSL bromine within the TTL, and its consequent stratospheric injection, is highly dependent on the oceanic flux, the strength of convection and the occurrence of heterogeneous recycling reactions. Our calculations indicate atomic Br should be the dominant inorganic species in large regions of the TTL during daytime, due to the low ozone and cold conditions of this region. We propose the existence of a "tropical ring of atomic bromine" located approximately between 15 and 19 km and between 30° N and 30° S. Daytime Br / BrO ratios of up to ~ 4 are predicted within this inhomogeneous ring in regions of highly convective transport, such as the tropical Western Pacific. Therefore, we suggest that experimental programs designed to quantify the bromine budget of the TTL and the stratospheric injection of VSL biogenic bromocarbons should include a strategy for the measurement of atomic Br during daytime as well as HOBr and BrCl during nighttime.

Short summary
We propose the existence of a daytime “tropical ring of atomic bromine” surrounding the tropics at a height between 15 and 19km. Our simulations show that VSL bromocarbons produce increases of 3pptv for inorganic bromine and 2pptv for organic bromine in the tropical TTL on an annual average, resulting in a total stratospheric bromine injection of 5pptv. This result suggests that the inorganic bromine injected into the stratosphere may be larger than that from VSL bromocarbons.
Final-revised paper