Fluorinated Radical Reactions of Atmospheric Importance

摘要

The three main pathways for the destruction of organic molecules in the atmosphere are radical reactions mainly with OH, atom reactions mainly with O (~1D) and UV photolysis (Scientific, 1995). In these processes organic radicals are formed which react mainly with O_2 molecules and form peroxy radicals. The same mechanism is valid for partially fluorinated hydrocarbons and partially fluorinated ethers. These hydrofluoroethers are proposed as an alternative for chlorofluorocarbons. The rate constants for the reaction of OH with fluorinated ethers are in the range 2.10~8 ≤ k (cm~3mol~(-1) s~(-1)) ≤ 4.4.10~(10) under atmospheric conditions (Zhang et al, 1992; Orkin et al, 1999; Tokuhashi et al, 1999). The possible reaction schemes of the radicals are shown in Good et al. (1998). As alternative radical sources Cl atom and NO_3 radical reactions are mentioned in Hack et al. (1999) and Kambanis et al. (1998). Atmospheric measurements of Cl atom concentrations together with the measured rate constants (Kambanis et al, 1998), however, show that these reactions are of no significant importance as a degradation channel. NO_3, which is important in the atmospheric night chemistry, has been shown in the paper by Hack et al. (2001) to be too slow to be of importance.