Arctic chlorine chemistry

K. R. Chan, Chlorine Chemistry on Polar Stratospheric Cloud Particles in the Arctic Winter, Science, 261, 1130-1134 (1993a). 

Martinez M., Arnold T., and Perner D. (1999) The role of bromine and chlorine chemistry for arctic ozone depletion events in Ny-Alesund and comparison with model calculations. Ann. Geophys. 17, 941-956. 

L. Lait, M.R. Schoeberl, J.W. Elkins,and K.R. Chan, Chlorine chemistry on polar stratospheric cloud particles in the Arctic winter. Science 261, 1130, 1993. 

However, with the recent recognition of the potential importance of atomic chlorine and bromine under certain conditions in the Arctic at polar sunrise (e.g., see Barrie et al., 1988 and Niki and Becker, 1993), the potential for BrO and CIO chemistry has been reconsidered. As described in Chapter 6 J.4, at polar sunrise there is a rapid loss of ground-level 03 that appears to be associated with reaction with atomic bromine and at the same time, there is evidence that chlorine atoms are playing a major role in the organic removal (Jobson et al., 1994). This is consistent with reactions of sea salt particles generating atomic bromine and chlorine, although the exact nature of the reactions and halogen atom precursors remains unknown. 

Other secondary chlorine species (atomic Cl, CIO, ClOOCl etc.) have been made responsible for Arctic ozone depletion, whereas the sources of the chlorine atoms are poorly understood (Keil and Shepson 2006). The Cl atom reacts similarly to OH (e. g. in oxidation of volatile organic compounds Cai and Griffin 2006). However, the photolysis of HCl is too slow (even in the stratosphere) to provide atomic Cl. Thus, the only direct Cl source from HCl is due to its reaction with OH, but with a fairly low reaction rate constant (Rossi 2003). There are several chemical means of production of elemental Cl (and other halogens) from heterogeneous chemistry (see Chapter 5.8.2) in the troposphere the photolysis of chloroorganic is not very important, with a few exceptions (see Chapter 5.8.1). 

The ozone layer in the stratosphere filters the high-energy ultraviolet radiation out of the sunlight and in this way enables life on earth. Since midst of the seventies a drastic decrease in the ozone concentration above the antarctic region has been observed in September and October every year, and since 1990 also above the arctic region. Investigating the role of chlorine in the atmospheric chemistry it was found, that chlorofluorocarbons can reach the stratosphere, where they decompose and release halogens that affect the ozone layer [357]. 

---