We have used a global three-dimensional chemical transport model to quantify the impact of the very short-lived substances (VSLS) CHBr3 , CH2 Br2 , CHBr2 Cl, CHBrCl2 , CH2 BrCl and C2 H5 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 CH2 Br2 . 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, C2 H5 Br, CH2 BrCH2 Br, n-C3 H7 Br and i-C3 H7 Br. 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 C2 H5 Br and CH2 BrCH2 Br, 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.
