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

Abstract

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. © 2012 Author(s).