Ozone Depletion

Ozone Status

Ozone is a molecule with three oxgyent atoms. How does it affect life?:

- Ozone in the lower atmosphere (troposphere - below about 20 km) is a pollutant which causes climate change, photochemical smog and human respiratory diseases.

- Ozone in the upper atmosphere (stratosphere above about 20 km) absorbs ultraviolet-B radiation. Without stratospheric ozone, solar ultraviolet-B (UV-B) radiation can penetrate atmosphere and increase the risk of skin cancer, cataracts and immune system deficiencies.

Ozone is mainly created by the action of solar radiation near the equator and then moves with air currents towards the poles. The destruction of ozone by Chlorofluorocarbons (CFCs) thus leads to the ozone layer being thinnest at the poles. At the moment, 4.6% of Earth's surface is not covered by stratospheric ozone layer. The difference in the wind patters between the hemispheres leads to the greatest loss being over Antarctica and is commonly referred to as the "ozone hole" (see picture). Fortunately this is an area where there is little life to be affected. There are, however, indications that there climate change in the Arctic may lead to an ozone hole developing there.


What's the cause of ozone depletion?

The answer is Chlorofluorocarbons (CFCs) are the main cause of stratospheric ozone depletion. They split off chlorine atoms from the CFC molecules under ultraviolet radiation. The chlorine atoms react with ozone to form oxygen - ozone molecule is destroyed. One CFC molecule can destroy many ozone molecules due to it react with oxygen atoms to form chlorine atoms which trigger the upper reaction.

The 1985 Vienna Convention for the Protection of the Ozone Layer and its 1987 Montreal Protocol phased out the use of ozone-depleting substances which replaced by HCFCs. However, the CFC's stay in the atmosphere for a long time so it will only be in the middle of this century that the hole in the ozone layer is likely to decrease substantially.

Further,HCFCs also cause some ozone depletion so stopping using them is the next step we have to take!

See the graph to know more on how ozone particles are decomposed:

Ozone Depletion Process

Source:AP Environmental Science Chapter 16- Air, Water and Soils