Ozone is a chemical that is related to oxygen. Oxygen is usually found as a stable particle, called a molecule, that is made up of two atoms. However when another oxygen atom is added the oxygen molecule becomes ozone. This happens when oxygen is exposed to ultra-violet radiation. The oxygen molecule completely changes, instead of being essential for breathing life, it takes on quite different properties.

The problem of worldwide concern is due to a decrease in ozone. You may have heard a lot of talk about "the ozone layer". This is not a layer like a thick blanket as you may imagine, but is an area in the outer atmosphere where you can expect to find rather more ozone than elsewhere. These ozone molecules can be found anywhere, but they are more concentrated about twenty kilometres above the earth, in an area called the stratosphere. Here ultra-violet radiation from the sun reaches the outer atmosphere and hits oxygen molecules combining them to form ozone. Even so, the concentration of ozone is only about one molecule in every 100,000.

The ozone layer, or ozonoshere, is this area where you would expect to find this higher concentration of ozone. If all the ozone was brought to earth and spread evenly it would lie no thicker than a sunday newspaper.

Ozone screens out most (90%) of the harmful ultraviolet rays from the sun. The ultra-violet radiation that penetrates through the atmosphere has a number of effects both on plants and people. UV radiation causes sun tanning, and eye irritation, but also skin cancer. UNEP figures indicate that a 1% decrease in world ozone would increase skin cancers worldwide by 6%.

The ozone layer is threatened by a group of chemicals, originally thought to be "miracle" chemicals, called Chloroflourocarbons. They are used in all sorts of places, in refrigerators, as solvents, to propel materials from aerosol cans, and to create foams for creams. They easily evaporate and get up into the stratosphere. There they attack the ozone breaking it back down to oxygen.

People were alerted to what was happening in the mid 1970s. UNEP launched a project in 1975 to identify hazards threatening the ozone layer.

In 1985 the ozone layer over the antarctic region was found to be particularly thin. This thin layer became known as "the hole"in the ozone layer. In 1987 in Montreal a Protocol was adopted and signed by 62 countries and the European Community. The agreement pledged to reduce the use of CFCs to half and to freeze the use of halons.

There are a number of connections between the ozone layer and the greenhouse effect.

• CFCs are greenhouse gases as well as ozone depleters.

• Depletion of the ozone layer allows more radiation on earth to hit the earth increasing the input of heating

• Some CFC substitutes are greenhouse gases themselves eg hydrocarbons

• CFCs will contribute to both global warming and the ozone depletion long after they have been banned.

CFCs

Chloroflurocarbons (CFCs) are synthetic chemicals that contribute to the depletion of the ozone layer found in the stratosphere. Ozone is made up of three oxygen atoms and CFCs contain chlorine atoms, chlorine chemistry is very complex. A chlorine atom can destroy ozone catalytically.

After being released CFCs remain in the troposphere, the layer of atmosphere above the earth where our weather is generated, they eventually rise into the upper stratosphere, above the ozone concentration. Once up there ultraviolet radiation from the sun breaks the CFC molecules apart so freeing the chlorine atoms, these attack ozone. A chlorine atom first steals one of the oxygen atoms from ozone so breaking the molecule apart to form chlorine monoxide and a stable oxygen molecule. These atoms and molecules are not still but are constantly jostling around in the stratosphere. When a chlorine monoxide molecule bumps into another oxygen atom, the two oxygen atoms combine easily, freeing the chlorine atom to continue destroying another ozone molecule.

Some chemical processes interfere with this catalytic cycle. Nitrogen dioxide (NO2) can bind to chlorine monoxide and form a chlorine reservoir - whilst chlorine is bound in this way it cannot react with ozone.

The unique climatic conditions at the south pole minimize such interference, allowing the catalytic conversion of ozone destruction to continue without interference so causing the ozone hole.

Reduction in the use of CFC's will not reduce the effect that chlorine atoms are now having on the ozone layer. In order not to make the situation worse further emissions should be halted if the ozone layer is to stand any chance of recovery.

OZONE DEPLETION

History

The Vienna Convention for the Protection of the Ozone Layer (1985)

The United Nations Environment Programme (UNEP) addressed the issue of ozone depletion in 1977. Governments committed themselves to protect the ozone layer and to co-operate with each other in scientific research through the Vienna Convention on the Protection of the Ozone Layer in 1985,


The Montreal Protocol on Substances that Deplete the Ozone Layer (1987)

Since then there have been many changes, in particular the Protocol in Montreal in 1987. Ozone Control is often referred to as the "Montreal Protocol". The Protocol aims to reduce and eventually eliminate the emissions of manufactured ozone depleting substances. The Montreal Protocol on Substances that Deplete the Ozone Layer was agreed by Governments in 1987. There have been a number of amendments since.

The London Amendment to the Montreal Protocol (1990)
The Copenhagen Amendment to the Montreal Protocol (1992)
Montreal Amendment to the Montreal Protocol (1997)

The Montreal Amendment entered into force on 1 January 1999. This version of the Montreal Protocol also includes the text of the Amendment adopted by the Parties at the Ninth Conference of the Parties in Montreal 1997.This laid down the following schedule for the phase out of ozone depleting substances

Phase Out Schedule

Control measures that apply to:

• developed countries are indicated by (c)

• developing countries are indicated by *

Outstanding environmental issues:

1. Several gases that are being used as ozone-safe replacements for CFCs - notably hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs) - also contribute to global warming.

2. Global warming may slow the ozone layer's healing process because the warming of the atmosphere near the ground may cause the stratosphere to become even colder.

3. There is non-compliance with the Montreal Protocol on the part of eight countries. Members of the former Soviet Union have been unable to meet their phase-out schedules due to their recent transition to market economies.

4. A number of new substances (namely Chlorobromomethane, n-propylbromide and Halon-1202) can be marketed as replacements for stronger ozone-depleting substances controlled under the Protocol even though they themselves have some ozone-depleting potential.

5. Concentrations of halons have continued to increase due to halons' long atmospheric lifetime and releases from fire extinguishers.

Summary

CFC Phaseout Schedules:
Allowed Production and Consumption for Developed Countries (percent of baseline)

From 1 January 2002, discarded fridges need to have the insulation foam removed before the fridge can be recycled or scrapped, to prevent the release of CFCs into the environment.

For information about Fridges and Ozone Depleting Substances Regulation

For latest UN information visit: http://www.unep.org/ozone/