1. What topic are we going to look at?

4. Ozone is an allotrope of Oxygen
It is O3 while normal oxygen is O2
Ozone absorbs harmful Ultra Violet [UV] rays from the sun
UV rays damage nuclear material in cells [DNA]
UV rays cause sunburn and skin cancer

5. O3 formed in upper part of the Stratospherekm
100
Thermosphere 80
Mesosphere
O3 formed in upper part of the Stratosphere
km up. 50
Ozone Layer
Stratosphere 25 15
Troposphere

6. Formation of Ozone O + O2 = O3
UV of high energy splits an oxygen molecule
O2 = O + O
Called photodissociation [breaking of a bond using light]
Each oxygen atom is called a free radical
It is very reactive and immediately reacts with an oxygen molecule O +
O2 = O3

7. Ozone is made in the ozone layer by UV light
Formation of O3 absorbs lots of UV
Ozone is also made in the sea
In very low concentrations it makes you feel good - this is what makes sea air so refreshing [Ozonisers]
It is made by electric motors - [sparks]
It is poisonous even in moderate concentrations.

8. High efficiency sterilisation Sterilisation using ozone is 1
High efficiency sterilisation Sterilisation using ozone is times quicker than ultraviolet light and up to 3000 times quicker than chlorine. Many Applications. Ozone can be used for killing germs, viruses, parasites and microbes. In addition it has a clearing effect, removes odours and clears poisonous / harmful chemicals. It also can aid in curing tail rot, erythema, scale disease and mould. Economical and Convenient It only uses air and oxygen as raw materials, therefore requiring no medicines and additives. Power output only 10 watts
OZONISER

9. Screening Effect of Ozone
(1) Formation of ozone absorbs some UV
(2) Ozone breakdown absorbs UV radiation when photodissociation takes place
UV absorbed O3 O2 + = O
Most of the oxygen radicals [atoms] formed in this way react with oxygen molecules to form ozone again.
In this way harmful UV is absorbed and ozone is not depleted
SCC Science Dept

10. O3 forms a layer in the upper atmosphere
It is destroyed by CFC’s - chloro-fluoro- carbons which are used as propellants for aerosols and in fridges
The O3 layer is getting thinner and is shown by holes appearing at the N and S poles [BAS 1984]
This allows more UV in and increases the chances of skin cancer

11. SCC Science Dept

12. Natural Destruction of Ozone
Some ozone is lost because
A few oxygen radicals react with ozone forming oxygen molecules O + O3 =
2 O2
Ozone destroyed at same rate formed.
British Antarctic Survey 1984 discovered a hole
SCC Science Dept

13. CFCs and UV CCl3F CCl2F + Cl O3 + Cl O2 + ClO + ClO + O Cl O2
Cl radical very reactive - attacks O3 O3 + Cl O2 +
ClO
Chlorine oxide is very reactive and attacks an oxygen atom as follows +
ClO + O Cl O2
Chlorine atom is reformed and can now attack another O3
One Cl atom can destroy > 10,000 O3