Ozone becoming oxygen is the basic reaction of ozone depletion, during which OH·,NO·,Cl· and Br· act as catalysts for ozone destruction cycles in the stratosphere. Among these catalysts, OH· and NO· mainly come from the nature, however, Cl· and Br· are mostly released by human. Furthermore, CFC and Halons are the major sources of Cl· and Br· in the stratosphere.
An example of reaction is shown below (CF2Cl2 is involved in CFC) :
CF2Cl2 → CF2Cl· + ·Cl
Cl· + O3 —→ ClO· + O2
ClO· + O —→ Cl· + O2
This process is able to produce ClO and Cl again and again; thus, a small amount of CFC will consume of ozone until it is transported to out of the stratosphere.
The reason why CFC and Halon are the major sources of catalysts is that CFC and Halon are stable in the troposphere which can reach to stratosphere and break down, thus producing Cl and Br which is able to consume ozone. However, recently, scientists found that short-lived compounds like CH2Cl2 could also release Cl· and lead to ozone depletion. What's more, it rose by 8% from 2004 to 2014 and may result fromf fast-rising emissions of a chemical used in paint stripper.
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