Atmospheric Chemistry and Physics, vol. 12, issue 1 (2012) pp. 371-380
We have used a global three-dimensional chemical transport model to
quantify the impact of the very short-lived substances (VSLS) CHBr3,
CH2Br2, CHBr2Cl, CHBrCl2, CH2BrCl and C2H5-Br on the bromine budget
of the stratosphere. Atmospheric observations of these gases allow
constraints on surface mixing ratios that, when incorporated into
our model, contribute ~4.9–5.2 parts per trillion (ppt) of inorganic
bromine (Bry) to the stratosphere. Of this total, ~76 % comes from
naturally-emitted CHBr3 and CH2Br2. The remaining species individually
contribute modest amounts. However, their accumulated total accounts
for up to ~1.2 ppt of the supply and thus should not be ignored.
We have compared modelled tropical profiles of a range of VSLS with
observations from the recent 2009 NSF HIPPO-1 aircraft campaign.
Modelled profiles agree reasonably well with observations from the
surface to the lower tropical tropopause layer.
We have also considered the poorly studied anthropogenic VSLS, C2H5Br,
CH2BrCH2Br, n-C3H7Br and i-C3H7Br. We find the local atmospheric
lifetime of these species in the tropical tropopause layer are ~183,
603, 39 and 49 days, respectively. These species, particularly C2H5Br
and CH2BrCH2Br, would thus be important carriers of bromine to the
stratosphere if emissions were to increase substantially. Our model
shows ~70–73 % and ~80–85 % of bromine from these species in the
tropical boundary layer can reach the lower stratosphere.
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