Articles | Volume 10, issue 5
Atmos. Chem. Phys., 10, 2269–2286, 2010
Atmos. Chem. Phys., 10, 2269–2286, 2010

  04 Mar 2010

04 Mar 2010

Finding the missing stratospheric Bry: a global modeling study of CHBr3 and CH2Br2

Q. Liang1,2,*, R. S. Stolarski1, S. R. Kawa1, J. E. Nielsen3,4, A. R. Douglass1, J. M. Rodriguez1, D. R. Blake5, E. L. Atlas6, and L. E. Ott3,7 Q. Liang et al.
  • 1NASA Goddard Space Flight Center, Atmospheric Chemistry and Dynamics Branch, Code 613.3, Greenbelt, MD 20771, USA
  • 2Oak Ridge Associated Universities, NASA Postdoctoral Program, Oak Ridge, Tennessee 37831, USA
  • 3NASA Goddard Space Flight Center, Global Modeling and Assimilation Office, Code 610.1, Greenbelt, MD 20771, USA
  • 4Science Systems and Applications Inc., Lanham, Maryland, USA
  • 5University of California, 570 Rowland Hall, Irvine, CA 92697, USA
  • 6University of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149, USA
  • 7Goddard Earth Sciences & Technology Center, University of Maryland, Baltimore County, Maryland, USA
  • *now at: Goddard Earth Sciences & Technology Center, University of Maryland, Baltimore County, Maryland, USA

Abstract. Recent in situ and satellite measurements suggest a contribution of ~5 pptv to stratospheric inorganic bromine from short-lived bromocarbons. We conduct a modeling study of the two most important short-lived bromocarbons, bromoform (CHBr3) and dibromomethane (CH2Br2), with the Goddard Earth Observing System Chemistry Climate Model (GEOS CCM) to account for this missing stratospheric bromine. We derive a "top-down" emission estimate of CHBr3 and CH2Br2 using airborne measurements in the Pacific and North American troposphere and lower stratosphere obtained during previous NASA aircraft campaigns. Our emission estimate suggests that to reproduce the observed concentrations in the free troposphere, a global oceanic emission of 425 Gg Br yr−1 for CHBr3 and 57 Gg Br yr−1 for CH2Br2 is needed, with 60% of emissions from open ocean and 40% from coastal regions. Although our simple emission scheme assumes no seasonal variations, the model reproduces the observed seasonal variations of the short-lived bromocarbons with high concentrations in winter and low concentrations in summer. This indicates that the seasonality of short-lived bromocarbons is largely due to seasonality in their chemical loss and transport. The inclusion of CHBr3 and CH2Br2 contributes ~5 pptv bromine throughout the stratosphere. Both the source gases and inorganic bromine produced from source gas degradation (BryVSLS) in the troposphere are transported into the stratosphere, and are equally important. Inorganic bromine accounts for half (2.5 pptv) of the bromine from the inclusion of CHBr3 and CH2Br2 near the tropical tropopause and its contribution rapidly increases to ~100% as altitude increases. More than 85% of the wet scavenging of BryVSLS occurs in large-scale precipitation below 500 hPa. Our sensitivity study with wet scavenging in convective updrafts switched off suggests that BryVSLS in the stratosphere is not sensitive to convection. Convective scavenging only accounts for ~0.2 pptv (4%) difference in inorganic bromine delivered to the stratosphere.

Final-revised paper