The contribution of natural and anthropogenic very short-lived species to stratospheric bromine

We have used a global three-dimensional chemical transport model to quantify the impact of the very short-lived substances (VSLS) CHBr ₃, CH ₂Br ₂, CHBr ₂Cl, CHBrCl ₂, CH ₂BrCl and C ₂H ₅-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 (Br _y) to the stratosphere. Of this total, ∼76 % comes from naturally-emitted CHBr ₃ and CH ₂Br ₂. 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, C ₂H ₅Br, CH ₂BrCH ₂Br, n-C ₃H ₇Br and i-C ₃H ₇Br. 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 C ₂H ₅Br and CH ₂BrCH ₂Br, 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.