Determination of the atmospheric lifetime and global warming potential of sulfur hexafluoride using a three-dimensional model

• Published in: Atmospheric Chemistry and Physics
• Main Authors: Kovács, Tamás, Feng, Wuhu, Totterdill, Anna, Plane, John M. C., Dhomse, Sandip, Gómez-Martín, Juan Carlos, Stiller, Gabriele P., Haenel, Florian J., Smith, Christopher, Forster, Piers M., García, Rolando R., Marsh, Daniel R., Chipperfield, Martyn P.
• Format: Text
• Language: English
• Published: 2018
• Subjects: Sodankylä
• Online Access: https://doi.org/10.5194/acp-17-883-2017; https://www.atmos-chem-phys.net/17/883/2017/

We have used the Whole Atmosphere Community Climate Model (WACCM), with an updated treatment of loss processes, to determine the atmospheric lifetime of sulfur hexafluoride (SF 6 ). The model includes the following SF 6 removal processes: photolysis, electron attachment and reaction with mesospheric metal atoms. The Sodankylä Ion Chemistry (SIC) model is incorporated into the standard version of WACCM to produce a new version with a detailed D region ion chemistry with cluster ions and negative ions. This is used to determine a latitude- and altitude-dependent scaling factor for the electron density in the standard WACCM in order to carry out multi-year SF 6 simulations. The model gives a mean SF 6 lifetime over an 11-year solar cycle ( τ ) of 1278 years (with a range from 1120 to 1475 years), which is much shorter than the currently widely used value of 3200 years, due to the larger contribution (97.4 %) of the modelled electron density to the total atmospheric loss. The loss of SF 6 by reaction with mesospheric metal atoms (Na and K) is far too slow to affect the lifetime. We investigate how this shorter atmospheric lifetime impacts the use of SF 6 to derive stratospheric age of air. The age of air derived from this shorter lifetime SF 6 tracer is longer by 9 % in polar latitudes at 20 km compared to a passive SF 6 tracer. We also present laboratory measurements of the infrared spectrum of SF 6 and find good agreement with previous studies. We calculate the resulting radiative forcings and efficiencies to be, on average, very similar to those reported previously. Our values for the 20-, 100- and 500-year global warming potentials are 18 000, 23 800 and 31 300, respectively.