Ozone Layer

What is the Ozone Layer?

Ozone is a naturally occurring gas found in the atmosphere where it absorbs most of the sun's ultraviolet light - invisible rays which are harmful to both plant and animal life.

Ozone is found throughout the atmosphere including ground level, but is mostly found in a band called the ozone layer at about 15 - 40km above the Earth's surface. The ozone layer is essential for life - until it was formed, about a billion years ago, the only life on Earth was at the bottom of the ocean.

At lower levels in the atmosphere ozone acts as a greenhouse gas helping trap heat and so contributes to global warming.

Destruction of the Ozone Layer - The Causes

Chlorofluorocarbons (CFCs) have been identified as the main cause of the destruction to the ozone layer, but also compounds containing bromine, other halogen compounds and also nitrogen oxides. CFCs are found in refrigerators, air conditioning packaging and propellants. They were discovered by Thomas Midgeley in 1930 as a cheap, safe coolant for refrigerators. CFCs are very stable, they decay slowly and so endure in the atmosphere for up to a century.

CFCs rise and gradually accumulate in the stratosphere where they are broken down by the sun's ultraviolet light, so releasing chlorine atoms. The chlorine attacks the ozone, one chlorine atom can help to destroy 100,000 ozone molecules.

The Effects

With the chlorine from CFCs destroying the ozone, more ultraviolet light is able to reach the Earth's surface, with harmful effect to human and plant life. The harmful radiation is known as UV-B.

UV-B radiation can cause skin cancer, cataracts and increased infections through the skin. It has an adverse effect on plants. It is also a threat to phyto-plankton, the single cell plants that all marine life depends on, as they are highly sensitive to UV-B radiation. This could upset the ocean food chain on which we depend for fish and also much of our oxygen.

Skin cancer is the most obvious problem as it is estimated that a 10% loss of ozone above Britain could cause an extra 8,000 cases of skin cancer every year.

The Antartic Ozone Hole

A hole in the ozone layer, covering an area larger than the Antarctic continent, was discovered in 1985 by Joe Farman and his colleagues on the British Antarctic Survey. They discovered a general thinning over the whole globe - a 3% decrease since 1969, but with greater depletions in middle and higher northern latitudes in winter. Every winter the ozone layer has been thinning by up to 8% over Europe.

Although there is no hole over the Arctic, experts have found that concentrations of chlorine are 50 times greater than expected.

In 1979 the USA and Scandinavia banned CFCs in aerosols. In 1985 the United Nations Convention on Protection of the Ozone Layer was drawn up. This was the first practical step towards limiting CFCs.

On 1st January 1989 the Montreal Protocol came into force. It is the actual agreement to reduce consumption of CFCs. Two revisions of this agreement have been made since then, the latest being in 1992. Thirty-three nations and the European Community have signed, committing them to cut CFC production by half by 2000. From the 1st January 2000 CFCs were banned from all new refrigerators and freezers. However the developing countries, such as India and China, are allowed to continue using CFCs until the year 2010.

Green consumerism can contribute towards saving the ozone layer. 'CFC-free'aerosol cans and plastic foam containers are now available to buyers. The Environmental Health Officer can arrange to take away old fridges so that the CFCs can be recovered and recycled. All fridge manufacturers in the European Union have to accept back their old fridges and dispose of the components safely. Most manufacturers now offer fridges with the CFCs in the insulation panels cut by at least 50%.

It is necessary to achieve the global-phase out of CFCs very quickly. The US Environmental Protection Agency (EPA) reported that, even if all countries successfully phased out CFCs by 1990, it would take until 2050 for the level of chlorine in the stratosphere to return to 1985 levels. This is because CFCs decompose so slowly.