Mesospheric Removal of Very Long-Lived Greenhouse Gases SF sub(6) and CFC-115 by Metal Reactions, Lyman- alpha Photolysis, and Electron Attachment

The fluorinated gases SF sub(6) and C sub(2)F sub(5)Cl (CFC-115) are chemically inert with atmospheric lifetimes of many centuries which, combined with their strong absorption of IR radiation, results in unusually high global warming potentials. Very long lifetimes imply that mesospheric sinks could...

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Bibliographic Details
Published in:The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2015-03, Vol.119 (10), p.2016-2025
Main Authors: Totterdill, Anna, Kovacs, Tamas, Martin, Juan Carlos Gomez, Feng, Wuhu, Plane, John MC
Format: Article
Language:English
Subjects:
Air pollution
Atmospherics
Electron attachment
Emission analysis
Global warming
Greenhouse effect
Photolysis
Reaction kinetics
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Summary:The fluorinated gases SF sub(6) and C sub(2)F sub(5)Cl (CFC-115) are chemically inert with atmospheric lifetimes of many centuries which, combined with their strong absorption of IR radiation, results in unusually high global warming potentials. Very long lifetimes imply that mesospheric sinks could make important contributions to their atmospheric removal. In order to investigate this, the photolysis cross sections at the prominent solar Lyman- alpha emission line (121.6 nm), and the reaction kinetics of SF sub(6) and CFC-115 with the neutral meteoric metal atoms Na, K, Mg, and Fe over large temperature ranges, were measured experimentally. The Na and K reactions exhibit significant non-Arrhenius behavior; quantum chemistry calculations of the potential energy surfaces for the SF sub(6) reactions indicate that the Na and K reactions with SF sub(6) are probably activated by vibrational excitation of the F-SF sub(5) (v sub(3)) stretching mode. A limited set of kinetic measurements on Na + SF sub(5)CF sub(3) are also presented. The atmospheric removal of these long-lived gases by a variety of processes is then evaluated. For SF sub(6), the removal processes in decreasing order of importance are electron attachment, VUV photolysis, and reaction with K, Na, and H. For CFC-115, the removal processes in decreasing order of importance are reaction with O( super(1)D), VUV photolysis, and reaction with Na, K, and H.
ISSN:1089-5639
1520-5215
DOI:10.1021/jp5123344