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

R Hossaini,E Atlas,M P Chipperfield,S A Montzka,J Elkins,W Feng,T J Breider,F Moore,B R Miller

doi:10.5194/acp-12-371-2012

Abstract

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 C2H5-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 (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.

Highlights

The bromine (Br) budget of the stratosphere is largely controlled by anthropogenic emissions of long-lived source gases (SGs) such as halons (e.g. CBrF3) and methyl bromide (CH3Br)
It has been suggested that very short-lived substances (VSLS) of predominately natural origin may provide an additional source of stratospheric inorganic bromine (BrVy SLS) (e.g., Sturges et al, 2000; Dorf et al, 2008)
We compare with aircraft observations in the tropics (± 20◦) from the recent NSF HIPPO-1 campaign (January 2009, http://hippo.ornl.gov/)

Summary

Introduction

The bromine (Br) budget of the stratosphere is largely controlled by anthropogenic emissions of long-lived source gases (SGs) such as halons (e.g. CBrF3) and methyl bromide (CH3Br). It has been suggested that very short-lived substances (VSLS) of predominately natural origin may provide an additional source of stratospheric inorganic bromine (BrVy SLS) (e.g., Sturges et al, 2000; Dorf et al, 2008). The magnitude of this supply is thought to be 6(3–8) ppt, representing ∼25 % of total stratospheric bromine (Montzka and Reimann et al, 2011). Hossaini et al.: Natural and anthropogenic very short-lived species date, most model work has focused on quantifying the stratospheric Bry supply from these VSLS (e.g., Hossaini et al, 2010; Liang et al, 2010) These studies estimate a supply of ∼2.4 and 5 ppt, respectively.

Model description

Modelled tracer profiles

Archived versus diagnosed convection

Source gas local lifetimes

Modelled total bromine

Conclusions