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Figure 4.38 Measured mid-latitude profiles of HF and COF,. COFC1 is derived from a model. (After Sen c! al. |1381, Figure 9.)

4.6.2 Iodine

The chemistry of iodine and its implications for stratospheric O, loss are less well known than those of the other halogens discussed in this chapter (chlorine, bromine, and fluorine). Because the lifetime of iodocarbons, the iodine source gas, is a few days in the troposphere—compared to tropospheric lifetimes of years for CFCs—it has generally been assumed that these molecules do not survive long enough to be transported into the stratosphere. It has been speculated, however, that iodine source molecules, such as methyl iodide (CH,I), might be transported into the stratosphere in convective events. Should this iodine 1» released in the stratosphere, catalytic cycles involving iodine could catalyze O, loss in the stratosphere, (See Solomon et al. [140] for a review of the tropospheric sources and stratospheric chemistry of iodine.)

The importance of iodine can be seen in Figure 4.39, which shows what fraction of the chlorine, bromine, and iodine families are in the active 0,-destroying form. As the size of the halogen atom increases, the associated reservoir molecules (HX, XONO,, HOX) become more weakly bound. Attendant with the weakening of the reservoir species, a greater fraction of the family exists in the 0,-destroying forms

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