Ozone - Earth's Umbrella

The ozone layer is a protective layer of gas molecules located within the stratosphere. Ozone gas also exists in the troposphere and at ground level, but most is located within the stratospheric layer shown to the right.

Ozone layer location

The ozone layer is a layer of gas consisting of O3 molecules, called Ozone, that forms when free Oxygen molecules bond to O2 molecules.

Ozone molecular structure

Since 1928, Chlorofluorocarbons have been produced, originally as nonflammable refrigerants for use in refrigerators, and eventually for use in fire extinguishers, dry cleaning agents, pesticides, degrease, adhesives, and as propellants for aerosol products. 
As these CFCs have been released into the atmosphere, the level of ozone in the stratosphere has decreased.
As ozone levels in the stratosphere are depleted, more solar radiation penetrates the Earth’s atmosphere. This affect results in an increase in solar radiation reaching the Earth’s surface adding to an increase in surface temperature. In turn, global warming actually results in a warming of the troposphere, but a cooling of the stratosphere, hindering the ozone layer’s natural chemistry for repairs. According to a recent study, the phasing out of substances under the Protocol led to more reductions in greenhouse gases than what is foreseen under the Kyoto Protocol.

Ultra-violet radiations

After the discovery of ozone depletion in the late 1970’s, many countries agreed that something must be done worldwide to stop the production of man-made, ozone harmful products. The international community adopted the Vienna Convention in 1985 followed by the Montreal Protocol in 1987. 

Ozone hole 1979 - 2007

The latest reports confirm that it has led to the phasing out of about 95% of the consumption of ozone-depleting substances (ODS) listed in the agreement. In turn, this has led to the prospect of the ozone layer recovering by 2050 to 2075.
Furthermore, the phasing out of ozone-depleting substances has helped to fight climate change since many of these chemicals are also powerful greenhouse gases.

Chemical aspects of Ozone

• The molecule of Ozone (O3) consists of 3 oxygen atoms is unstable as compared to the Oxygen (O2) molecule. 
• It’s a very reactive gas with a pungent and irritating odor.
• Even in low concentration its toxic and harmful to health.
• It occurs naturally in earth’s upper atmosphere.
• It is a powerful oxidizing agent next to fluorine.
• Ozone was discovered in 1839 by a German scientist Christian Friedrich Schonbein.

Ozone O3 Molecular structure

 

PREPARATION OF OZONE

Siemen's ozonizer

• It consists of two co-axial glass tubes fused together.
• Tin foil is used to coat the inner-side of the inner tube and the outer-side of the outer tube. 
• The inner and outer tin coatings are connected to the terminals of an induction coil, which produces current of high voltage. 
• A slow current of pure and dry oxygen is passed through the annular space. On subjecting oxygen to silent electrical discharge, ozonized oxygen containing 10-15% ozone is formed. 
• By taking the following precautions, the yield of ozone can be increased in the ozonized oxygen:
• Only pure and dry oxygen should be used.
• The ozonizer should be perfectly dry.
• A fairly low temperature (around 0°C) should be maintained.
• There should be no sparking. 

 Brodie's ozoniser 

• In principle, this ozoniser is like the Siemen's ozoniser but dilute sulphuric acid replaces the tin foil. 
• Two carbon electrodes are dipped in the acid and connected to an induction coil.
• A current of dry oxygen is passed through the space between the tubes.
• Ozonized oxygen containing about 5% O3 comes out at the other end.
•  If the apparatus is kept cool, the proportion of ozone may go up 20-25%.