Reactions of Cl Atoms and CIO Radicals

The reactions of halogen atoms and radicals are of fundamental importance in stratospheric chemistry (see Sects. 4.4 and 8.2, 8.3, and 8.4), and the halogen cycle is also of interest in the marine boundary layer in the troposphere (see Sect. 7.5). In this section, among the atmospheric reactions of halogen atoms and radicals, fundamental homogeneous reactions of Cl atoms and CIO radicals are described, and the reactions of bromine and iodine atoms and radicals are discussed in the more phenomenological discussions in Chaps. 7 and 8. 

The reaction of Cl atoms and O3 is the direct dissipation reaction of O3 molecules in the ClOx cycle (Sect 8.2.3), and is important as a rate-determining step to reduce the equilibrium concentration of ozone by CH3CI in the natural stratosphere. 

Although the CH4 dissipation reaction by Cl atoms has an important role not only in the stratosphere but also possibly in the troposphere, the ratio of its importance relative to OH reaction has not been estimated quantitatively since the global emissions of inorganic chlorine from sea salt has not been evaluated yet. 

The measurements of rate constant of this reaction have been made extensively including relatively recent measurements for temperature dependence (Seeley et al. 1996b Pilgrim et al. 1997 Wang and Keyser 1999 Bryukov et al. 2002). Based on these and other measurements at 298 K, the NASA/JPL panel evaluation No. 17 (Sander et al. 2011) recommends. 

5 Homogeneous Elementary Reactions in the Atmosphere and Rate Constants 

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