• Due to human activity – human made chemicals that contain chlorine or bromine – known as ODS (Ozone Depleting Substances)
  • ODS float and remain static high up in the stratosphere – when up there ODS are broken down by the UV rays and resultant chemical is chlorine and bromine
  • Chlorine and bromine can strip off one oxygen atom the ozone molecule
  • ODS include: chlorofluorocarbons (CFCs), carbon tetrachloride, hydrochlorofluorocarbons (HCFCs) and methyl chloroform. Halons – brominated fluorocarbons also contribute.  
  • Natural causes: sun-spots, stratospheric winds and volcanic eruptions (1-2% and temporary)
  • Man made causes