Ozone Depleting Substance

Ozone is a naturally occurring molecule consisting of three oxygen atoms. It is present at low levels throughout the atmosphere but is more concentrated in the upper levels or the stratosphere.

It forms a highly reactive, corrosive, colourless gas which can attack surfaces, fabrics and rubber materials and is toxic to crops vegetation and trees at above average levels, meaning raised levels of ozone in the lower atmosphere are harmful to human health, vegetation and materials. However, in the upper atmosphere it forms a protective layer that shield the Earth from the sun's harmful ultraviolet (UV) radiation.

Ozone is continuously being naturally produced and destroyed in the stratosphere. UV radiation from the sun reacts with oxygen molecules, causing them to split to produce two unbound oxygen atoms. The free oxygen atom can collide and react with other oxygen molecules to produce ozone molecules, which consist of three oxygen atoms.

Conversely, when an ozone molecule absorbs UV radiation it then splits into its constituent parts, producing a free oxygen atom. The free oxygen atom may go on to collide and 'recombine' with another ozone molecule to produce two oxygen molecules. 

The production and destruction processes occur at similar rates in the upper atmosphere, which maintains ozone concentrations in the stratosphere. However, Ozone Depleting Substances, when allowed to escape into the atmosphere cause ozone to break down more quickly than usual, reducing the protective layer around the Earth.

 Typical ODS include:

  • CFCs
  • Halons
  • Carbon Tetrachloride
  • 1,1,1 Trichloroethane
  • HCFCs
  • Methyl Bromide

Common uses for ODS include:

  • refrigeration and air-conditioning equipment
  • aerosols
  • solvents
  • foam blowing agents
  • fire fighting fluids
  • high voltage switch gear.

However, many ODS are banned or being phased out due to their harmful effects. Their use is highly regulated and they can no longer be released to atmosphere. ODS can only be produced as a feedstock for producing non-ODS substances or for laboratory and analytical work.

For further information please refer to the NetRegs information page:

http://www.environment-agency.gov.uk/netregs/63167.aspx