Effects of electron and ion reactions on atmospheric lifetimes of fully fluorinated compounds

This is the authors' abstract. We don't add key points for this paper.

Atmospheric lifetimes are evaluated for the fully fluorinated compounds CF 4 , C 2 F 6 , c ‐C 4 F 8 , C 6 F 14 , and SF 6 using a two‐dimensional transport and chemistry model which includes removal by electrons and ions in the mesosphere and lower thermosphere. Laboratory measurements of the pertinent reaction rates were carried out at thermal energy for free electrons and for the atmospheric ions O + , O 2 + , O − , O 2 − , NO + , H 3 O + , NO 3 − , and CO 3 − . Atmospheric removal by electrons reduces the lifetimes of c ‐C 4 F 8 and SF 6 from about 3200 years to 1400 and 800 years, respectively, only if the respective product anions C 4 F 8 − and SF 6 − do not subsequently regenerate the parent neutral compounds. Atmospheric removal by ion reactions is minor or negligible, with the largest effect (∼5%) being removal of C 6 F 14 by O 2 + . Removal of CF 4 and C 2 F 6 by O + is probably the most important single destruction process in the atmosphere for these two compounds, but their lifetimes are governed by removal at the Earth's surface in high‐temperature combustors. While we show that the lifetimes of c ‐C 4 F 8 and SF 6 may be significantly shorter than previously estimated, these compounds remain extremely long‐lived with significant global warming potentials.