The contribution of natural and anthropogenic very short-lived species to stratospheric bromine
We have used a global three-dimensional chemical transport model to\nquantify the impact of the very short-lived substances (VSLS) CHBr3,\nCH2Br2, CHBr2Cl, CHBrCl2, CH2BrCl and C2H5-Br on the bromine budget\nof the stratosphere. Atmospheric observations of these gases allow\nconstraints on surface mixing ratios that, when incorporated into\nour model, contribute ~4.9–5.2 parts per trillion (ppt) of inorganic\nbromine (Bry) to the stratosphere. Of this total, ~76 % comes from\nnaturally-emitted CHBr3 and CH2Br2. The remaining species individually\ncontribute modest amounts. However, their accumulated total accounts\nfor up to ~1.2 ppt of the supply and thus should not be ignored.\nWe have compared modelled tropical profiles of a range of VSLS with\nobservations from the recent 2009 NSF HIPPO-1 aircraft campaign.\nModelled profiles agree reasonably well with observations from the\nsurface to the lower tropical tropopause layer. \n\n\nWe have also considered the poorly studied anthropogenic VSLS, C2H5Br,\nCH2BrCH2Br, n-C3H7Br and i-C3H7Br. We find the local atmospheric\nlifetime of these species in the tropical tropopause layer are ~183,\n603, 39 and 49 days, respectively. These species, particularly C2H5Br\nand CH2BrCH2Br, would thus be important carriers of bromine to the\nstratosphere if emissions were to increase substantially. Our model\nshows ~70–73 % and ~80–85 % of bromine from these species in the\ntropical boundary layer can reach the lower stratosphere.