Chloride nitrate , stratospheric

Let us now return to the chemistry associated with the depletion of stratospheric ozone. Most of the chlorine and chlorine oxide released into the stratosphere by Reactions (7.34) and (7.35) are quickly tied up in reservoirs as hydrogen chloride and chloride nitrate by the reactions... 

Abstract Heterogeneous chemical reactions at the surface of ice and other stratospheric aerosols are now appreciated to play a critical role in atmospheric ozone depletion. A brief summary of our theoretical work on the reaction of chlorine nitrate and hydrogen chloride on ice is given to highlight the characteristics of such heterogeneous mechanisms and to emphasize the special challenges involved in the realistic theoretical treatment of such reactions. 

During the dark, polar winter the temperature drops to extremely low values, on the order of-80°C. At these temperatures, water and nitric acid form polar stratospheric clouds. Polar stratospheric clouds are important because chemical reactions in the stratosphere are catalyzed on the surface of the crystals forming these clouds. The chemical primarily responsible for ozone depletion is chlorine. Most of the chlorine in the stratosphere is contained in the compounds hydrogen chloride, HCl, or chlorine nitrate, CIONO. Hydrogen chloride and chlorine nitrate undergo a number of reactions on the surface of the crystals of polar stratospheric clouds. Two important reactions are ... 

Haas, B.-M., K. C. Crellin, K. T. Kuwata, and M. Okumura, Reaction of Chloride Ions with Chlorine Nitrate and Its Implications for Stratospheric Chemistry, J. Phys. Chem., 98, 6740-6745 (1994). 

Tolbert, M. A., M. J. Rossi, R. Malhotra, and D. M. Golden, Reaction of Chlorine Nitrate with Hydrogen Chloride and Water at Antarctic Stratospheric Temperatures, Science, 238, 1258-1260 (1987). 

F. S. Rowland, Chlorofluorocarbons and the depletion of stratospheric ozone Am. Sci. 77, 36-45 (1989) T.-L. Tso, L. T. Molina, and F. C.-Y. Wang, Antarctic stratospheric chemistry of chlorine nitrate, hydrogen chloride and ice release of active chlorine. Science 238, 1253-1260 (1987) J. G- Anderson, D. W. Toohey, and W. H. Brune, Free radicals within the Antarctic vortex the role of CFCs in Antarctic ozone loss. Science 251, 39-46 (1991) P. S. Zurer, Complexities of ozone loss continue to challenge scientists. Chem. Eng. News June 12, 20-23 (1995). 

Only a small percentage of the chlorine released by photolysis of CFCs is present in the active forms as Cl or CIO, however. Most of it is bound up in reservoir compounds such as hydrogen chloride and chlorine nitrate, formed respectively by hydrogen abstraction (equation 10) from methane and addition (equation 11) to nitrogen dioxide. Slow transport of these reservoir species across the tropopause, followed by dissolution in tropospheric water and subsequent rain-out, provide sink processes for stratospheric chlorine. 

FIGURE 4-41 Key chemical processes of the Antarctic ozone hole. Of particular importance are the polar stratospheric clouds, which catalyze the release of ozone-destroying chlorine from chlorine nitrate and hydrogen chloride (Prinn and Hartley, 1992). 

Tolbert, M.A., M.J. Rossi, and D.M. Golden, Heterogeneous interactions of chlorine nitrate, hydrogen chloride and nitric acid with sulfuric acid surfaces at stratospheric temperatures. Geophys Res Lett 15, 847, 1988. 

Molina, M. J., T-L. Tso, L.T. Mohna, and F.C.-Y. Wang, Antarctic stratospheric chemistry of chlorine nitrate, hydrogen chloride, and ice Release of active chlorine,... 

Leu, M.-T., Moore, S.B., Keyser, L.L. Heterogeneous reactions of chlorine nitrate and hydrogen chloride on type I polar stratospheric clouds. J. Phys. Chem. 95, 7763-7771 (1991)... 

---