1. Ozone and CFCs
Intro

2. What is Ozone? Ozone is an allotrope of oxygen. It’s formula is O3.
It is naturally present in the atmosphere.
It exists both in the troposphere (lower atmosphere) and the stratosphere.

3. Ozone in the Stratosphere
90% of ozone is in the stratosphere
It absorbs ultraviolet radiation which can be harmful to life on earth.
Stratospheric ozone absorbs 97-99% of the sun’s ultraviolet radiation.
It is formed in the following way:
O2 (g) 2O (g)
O2 (g) + O (g)  O3 (g)

4. Ozone in the Troposphere
Ozone is harmful in the troposphere. It is toxic, and harmful to health at low concentrations (0.1 ppm)
It forms photochemical smog by reacting with exhaust gases from motor vehicles.
NO2 (g) + sunlight  NO (g) + O (g)
The oxygen radicals then react with O2, forming ozone.
O2 (g) + O (g)  O3 (g)

5. Chlorofluorocarbons (CFCs)
Synthetic chemicals
Contain fluorine, chlorine and carbon (no hydrogen)
Have a similar structure to alkanes, with hydrogen replaced by fluorine and chlorine.
E.g. Dichlorodifluoromethane

6. Source: Encyclopedia of the Atmospheric Environment
Uses of CFCs
Uses of CFCs Prior to the 1987 Montreal Protocol
Source: Encyclopedia of the Atmospheric Environment

7. CFCs and Ozone 1
CFCs are chemically inert and are not broken down at low altitudes. They are also insoluble in water so they are not washed from the atmosphere in rain.
They remain in the troposphere for long periods of time, and diffuse into the stratosphere.
CFCs in the stratosphere cause damage to the protective ozone layer.

8. CFCs and Ozone 2
CFCs are broken down by UV radiation in the stratosphere releasing halogen atoms, such as chlorine, which can react to break up ozone molecules.
CCl3F (g) + UV radiation  CCl2F (g) + Cl (g)
Cl (g) + O3  ClO (g) + O2 (g)
ClO then reacts with oxygen radicals
ClO (g) + O (g)  O2 (g) + Cl (g)
Since the chlorine atom is not used up in the reaction it can continue breaking up ozone molecules indefinitely.
This removes ozone from the stratosphere, meaning it cannot perform it’s purpose of absorbing harmful UV rays as effectively.

9. Source: Environmental Protection Agency, USA
Ozone Depletion
Source: Environmental Protection Agency, USA

10. The Hole in the Ozone Layer

11. Effects of Ozone Depletion
Global Warming
Increase in levels of skin cancer, cataracts, immune system impairment.
Impact on crops and agriculture
Impact on marine food cycle

12. CFC Alternatives
Impact of Chlorofluorocarbon Replacements on Stratospheric Ozone
Source:

13. CFCs, HCFCs and HFCs