| Halogenated very short-lived species (VSLS) are known to provide an additional supply of
inorganic bromine (Bry) to the stratosphere (e.g. WMO, 2003). The magnitude of this supply
is uncertain with current estimates ranging from ~3-8 ppt. Furthermore, uncertainties exist as
to the relative importance of the so-called, source gas injection (SGI) and product gas
injection (PGI) pathways. This is enhanced by a lack of observational data, particularly of the
degradation products (aka. product gases, e.g.CBr2O) formed following the breakdown of
source gases (e.g. CHBr3) via reaction with OH or photolysis. Previous model work
has not directly considered the fate of these species and thus this is omission is
addressed.
A detailed chemical scheme describing the tropospheric degradation of CHBr3,
dibromomethane (CH2Br2) and other bromo/chloro-carbon source gases has been developed
for use in the TOMCAT/SLIMCAT 3D chemical transport model (CTM). We present results
from multi-annual simulations quantifying the contribution of these species to the
stratospheric halogen budget. We also present novel estimates of the degradation products of
these species in the tropical near-tropopause region. In addition, results are verified
with comparison of modelled source gas profiles with observations taken during
the 2007 NASA TC4 campaign. Sensitivity runs investigating the importance of
convection and also the lifetime of Bry due to washout have also been performed |