Explain how a small amount of chlorofluorocarbons can destroy a large amount of ozone.

Chlorofluorocarbons (CFCs) are molecules made up of chlorine, fluorine and carbon atoms and are extremely stable. CFCs are mainly responsible for chemical ozone depletion (reduction of the amount of ozone in the stratosphere). Ozone molecules (O3)  are very important in the stratosphere because they can absorb potentially damaging ultraviolet (UV) radiation.The extreme stability of CFCs allows them to make their way into the stratosphere (most molecules decompose before they can cross into the stratosphere from the troposphere) and to reach great altitudes where photons are more energetic. When the CFCs come into contact with these high energy photons, their individual components are freed. The chlorine atoms can break down tens of thousands of ozone molecules before being removed from the stratosphere. The following reaction displays how Cl- atoms have an ozone-destroying cycle:

Cl⁻+O₃→ClO+O₂

ClO+O°→Cl-+O₂

O₃+O°→2O₂

CFCs were in widespread use, for example, in air conditioning and cooling units, as aerosol spray propellants prior to the 1970s.

The chlorine in chlorofluorocarbons is broken from the molecule by ultraviolet radiation. The free chlorine then combines with an oxygen atom from ozone, leaving an oxygen molecule and forming chlorine monoxide. Free molecules of oxygen can displace the chlorine in chlorine monoxide, leaving chlorine free to break up another molecule of ozone. One chlorine atom can destroy up to 100,000 ozone molecules.

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