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

Hossaini, R. and Chipperfield, M. P. and Feng, W. and Breider, T. J. and Atlas, E. and Montzka, S. A. and Miller, B. R. and Moore, F. and Elkins, J. (2012) The contribution of natural and anthropogenic very short-lived species to stratospheric bromine. Atmospheric Chemistry and Physics, 12 (1). pp. 371-380. ISSN 1680-7316

Abstract

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 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 similar to 4.9-5.2 parts per trillion (ppt) of inorganic bromine (Br-y) to the stratosphere. Of this total, similar to 76% comes from naturally-emitted CHBr3 and CH2Br2. The remaining species individually contribute modest amounts. However, their accumulated total accounts for up to similar 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 similar to 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 similar to 70-73% and similar to 80-85% of bromine from these species in the tropical boundary layer can reach the lower stratosphere.