1. CFCs and other ozone-depleting substances (ODS): These compounds, which were widely used in refrigerants, aerosols, and other products, contain chlorine and bromine.
2. UV radiation: When these ODS reach the stratosphere (where the ozone layer resides), they are broken down by ultraviolet (UV) radiation from the sun.
3. Chlorine atom release: This breakdown releases chlorine atoms, which are highly reactive.
The ozone depletion cycle:
The chlorine atoms then participate in a catalytic cycle that destroys ozone:
1. Chlorine atom reacts with ozone: A chlorine atom reacts with an ozone molecule (O3), breaking it down into oxygen (O2) and a chlorine monoxide molecule (ClO).
2. Chlorine monoxide reacts with an oxygen atom: The chlorine monoxide then reacts with a free oxygen atom (O) to form another oxygen molecule and regenerate the chlorine atom.
This regenerated chlorine atom can then go on to destroy another ozone molecule, continuing the cycle.
Therefore, chlorine atoms are not formed in the ozone layer but are introduced through human-made chemicals. Their presence initiates a chain reaction that leads to the depletion of ozone.
