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

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...

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Bibliographic Details
Published in:Atmospheric Chemistry and Physics
Main Authors: T. Kovács, W. Feng, A. Totterdill, J. M. C. Plane, S. Dhomse, J. C. Gómez-Martín, G. P. Stiller, F. J. Haenel, C. Smith, P. M. Forster, R. R. García, D. R. Marsh, M. P. Chipperfield
Format: Article in Journal/Newspaper
Language:English
Published: Copernicus Publications 2017
Subjects:
Physics
QC1-999
Chemistry
QD1-999
Sodankylä
Online Access:https://doi.org/10.5194/acp-17-883-2017
https://doaj.org/article/368f67a21ef1447d8274696940cdae70
Description
Summary: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.

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