Precious ozone: 30th anniversary of the Vienna Convention and International Ozone Day |21 September 2015
When future generations look back at our times, what might they consider the most
significant sustainable development actions we have taken, with far-reaching benefits?
We can only speculate, but the saving of the ozone layer will surely be among those they will recognise. It is an extraordinary and still ongoing success story of governments, experts and ordinary people coming together, responding to scientific findings, and acting resolutely to protect all life on Earth from the sun’s harmful ultraviolet rays.
This year marks the 30th anniversary of the Vienna Convention for the Protection of the Ozone Layer, an important milestone in the protection of the ozone layer. The theme for the celebration of the anniversary and this year’s international day for the preservation of the ozone layer marked on September 16 was ‘30 years of healing the ozone together’.
The theme is supported by the slogan ‘Ozone: All there is between you and UV’.
The international ozone day is an annual event that commemorates the date of the signing in 1987 of the Montreal Protocol on Substances that Deplete the Ozone Layer. In the last three decades, the Vienna Convention and its Montreal Protocol have galvanised 197 nations to work together on phasing out ozone-depleting substances, thus protecting the ozone layer for this and future generations and contributing significantly to global efforts to address climate change.
What is ozone and the ozone layer?
The ozone layer is a layer in the Earth's atmosphere containing high concentrations of ozone. It is typically said to exist between about 20km and 30km above the Earth's surface, but it does not have definite edges.
Ozone (O3) is a gas found in our atmosphere. Each ozone molecule is made up of three oxygen atoms. It is a pale blue gas with a distinctively pungent smell – and it is very scarce. Just 0.000004% of Earth’s total atmosphere is made up of ozone.
The ozone layerprotects us from harmful radiation from the sun. In particular, it protects us from UVB, which is a type of ultraviolet radiation. Small amounts of exposure to UVB can result in sunburn, but high levels of exposure would cause us – and most other life on earth – to die.
How have humans affected the ozone layer?
Since the mid-1970s scientists have been concerned about the harmful effects of certain chlorofluorocarbons (CFCs) on the ozone layer. These CFC compounds are relatively inert and nontoxic, and humans found a use for them as cooling agents in refrigerators and air conditioning systems among other things. Because they are so inert, when CFCs become discharged into the atmosphere they diffuse and do not decompose straight away – not until they are hit by shortwave UV radiation. This occurs in the ozone layer.
When a CFC is hit by UV radiation, it loses its chlorine atom. This chlorine atom acts as a catalyst. It is able to steal one oxygen atom away from an ozone molecule, leaving an oxygen molecule and chlorine oxide. Chlorine oxide can then react with a single oxygen atom to form an oxygen molecule and a chlorine atom. This cycle means the chlorine atom is free to break up another ozone molecule.
One chlorine atom can destroy up to 100,000 ozone molecules before it is removed by some other reaction. This can devastating for the ozone layer. It disrupts the delicate flux and causes ozone to be destroyed faster than it is created.
Polar stratospheric clouds also catalyse ozone depletion by active chlorine.
What have we done about ozone depletion?
In the mid-1970s, we became aware that the ozone layer was being depleted. In the 1980s we decided to do something about it. On the strength of growing evidence suggesting that CFCs were contributing to stratospheric ozone depletion, scientists urged nations to control their use of CFCs, and so the Vienna Convention for the Protection of the Ozone Layer was adopted in 1985, followed by the Montreal Protocol on Substances that Deplete the Ozone Layer in 1987. States party to the Montreal Protocol agreed to phase out the use of ozone-depleting chemicals and have strengthened the Protocol over the years, leading to a 98% reduction of the historic baseline levels of the ozone-depleting substances produced and consumed globally.
The Montreal Protocol is widely lauded as a huge environmental success. While the damage we have done to the ozone layer has not yet been undone, there is scientific evidence that the ozone layer is healing itself and is expected to recover by the middle of this century
Contributed by the Ministry of Environment, Energy and Climate Change