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      | 
      | 
      | 
      | 
      | 
      | 
   
   
    | q | 
    The ice crystals in the polar stratospheric clouds 
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     | 
   
   
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    provide surface for the ozone depletion surface to 
     | 
     | 
   
   
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    occur more easily. 
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     | 
   
   
     | 
   
   
    | q | 
    On these cloud surfaces, certain forms of chlorine 
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     | 
   
   
     | 
    that do not react with ozone are converted into 
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     | 
   
   
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     | 
    forms that do. 
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     | 
   
   
     | 
   
   
    | q | 
    Polar stratospheric clouds set up the stage for 
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     | 
   
   
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    massive destruction of ozone to happen when 
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     | 
   
   
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     | 
    sunlight returns in the spring. 
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     |