Causes of ozone depletion

• Scientific evidence shows that stratospheric ozone is destroyed by a group of manufactured chemicals containing chlorine and/or bromine
• This group of chemicals is known as ozone depleting substances (ODSs)
• These ODSs are very stable, non-toxic and environmentally friendly in the lower atmosphere
• However, their stability makes it possible for them to migrate upwards into the stratosphere
• In the stratosphere, the ODSs are broken up by ultraviolet rays and the chlorine and/or bromine atoms are released
• The chlorine atoms destroys ozone by removing an oxygen atom from the ozone molecule; a chlorine monoxide molecule is formed
• A free oxygen atom binds with the oxygen atom in the chlorine monoxide molecule and the chlorine atom is released to destroy another ozone molecule in the stratosphere
• ODSs have a very long lifespan (centuries) in the atmosphere
• The greater part of ODSs released into the atmosphere over the last 80 years are still making their way to the stratosphere where they will contribute to ozone depletion
• ODSs most commonly used are chlorofluorocarbons (CFCs); they are responsible for over 80% of the total stratospheric ozone depletion
• CFCs were used extensively as cooling agents in refrigerators, freezers, air conditioners and aerosol cans