CFCs affect the ozone layer by destroying ozone molecules. CFCs, or chlorofluorocarbons, are normally stable molecules, but when UV rays strike them, they are broken down. The chlorine atom released from a CFC wreaks havoc on ozone molecules.
Ozone molecules are made up of three atoms of oxygen instead of the usual two atoms that make up normal atmospheric oxygen. Ozone forms a protective layer in the stratosphere and shields Earth from the damaging rays of the sun, namely the sun's ultraviolet rays. At altitudes lower than the stratosphere, ozone becomes a pollutant and is a constituent of smog. Winds send CFCs into the upper atmosphere, or stratosphere.
When a UV ray strikes a CFC molecule, the chlorine comes free of the molecule. Chlorine is a highly reactive element, so chlorine atoms bind easily to whatever is available. The free chlorine atom encounters ozone molecules, binding to and tearing away a single oxygen atom. A molecule of chlorine monoxide forms and then meets up with a free oxygen atom. The two oxygen atoms bind, forming atmospheric oxygen, leaving the chlorine atom free to destroy another ozone molecule. According to the Environmental Protection Agency, a single chlorine atom can destroy tens of thousands of ozone molecules.
Because of this ozone-destroying process, the ozone layer is thinning over many parts of the world. With the Montreal Protocol of 1989, the international community has come together to phase out ozone-depleting substances.