The contribution of natural and anthropogenic very short-lived species to stratospheric bromine
1Institute for Climate and Atmospheric Science, School of Earth and Environment, University of Leeds, UK
2School of Engineering and Applied Sciences, Harvard University, Cambridge, USA
3Rosenstiel School of Marine and Atmospheric Science, University of Miami, USA
4National Oceanic and Atmospheric Administration, USA
Abstract. We have used a global three-dimensional chemical transport model to quantify the impact of the very short-lived species (VSLS) CHBr3, CH2Br2, CHBr2Cl, CHBrCl2, CH2BrCl and C2H5Br 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.