1. What is ozone depletion?

2. The Ozone layer
The ozone layer is a thin layer of the Earth’s atmosphere which helps prevent ultraviolet radiation from harming people and other living things.

3. Ozone in the stratosphere
A thin layer of ozone gas (03) encircles the earth, in the stratosphere.
03 is a natural occurring bluish gas which has an acrid odor. It has harmful effects on organisms however, it helps block out the harmful UV rays 15km to 45km up in the atmosphere.

4. The Ozone layer

5. FORMATION OF OZONE 1) O2  2 O* (Oxygen free radical)
The ozone is formed when the double bond in the oxygen is broken by very short wavelength UV-C light
2) O O*  O3
An oxygen free radical is therefore formed, this oxygen free radical further reacts with another oxygen atom to form ozone gas, O3.

6. OZONE DEPLETION
The reverse process happens when O3 absorbs longer wave length UV-B light. This is because two pi bonding electrons are shared between the entire structure therefore it has weaker bonds (longer bonds) compared to O2.
O3 (g)  O2 (g) + ●O (g) The oxygen free radicals react with another resonance structure to form O2. ●O (g) + O3 (g)  O2 (g)

7. STEADY STATE
As a result the rate of which Ozone is produced and depleted would be equal, this is known as the steady state.
The ozone helps protect the earth from 99% of the dangerous UV light of longer wavelength (240nm to 330 nm) than that absorbed by oxygen (less than 240 nm) and nitrogen by this process, however, this steady state is constantly being interfered with by ozone-depleting pollutants.

9. OZONE LAYER BEING REDUCED
There has been a clear decline over the last 30 years in ozone concentrations above the north and south poles, which is seasonal with the lowest levels being found in the Antarctic region during the spring (October).
Due to cold winter months and ice particles surface behaving as a catalyst for the photo –dissociation of chlorine molecules.

13. Ozone Hole Theories Chemistry vs Meteorology Human vs Natural
Solar Cycles

14. OZONE DEPLETING POLLUTANTS
The main pollutants includes: CFCs (Chlorofluorocarbons) and oxides of nitrogen. (NOx)
Sources
CFCs are mainly found in hair spray or deodorant cans as a propellant, old refrigerators, air conditioners e.t.c. Oxides of nitrogen are formed from high temperature reactions of N2 and O2 in supersonic aircraft engines and lightning.

16. REACTIONS FROM CFCs
CFC’s contain bonds which are relatively strong (H-F 484 kJ/mol, H-Cl 384 kJ/mol) so they don’t react easily. But as they float up toward the unfiltered UV light, the H-Cl bond can break and then produce a highly reactive Cl free radical.
CCl2F2 + uv light  .CClF Cl
.Cl + O3  ClO. + O2

17. REACTIONS FROM CFCs

18. REACTIONS FROM NOX NO + O3  NO2 + O2
NO O  NO O2 (what is the overall result)
Consequences are more UV light will reach the earth increasing the chances for skin cancer, sun burns, damage to animals and vegetation and even genetic mutations.

19. ALTERNATIVE TO CFCs
Properties required for substitutes are low reactivity, low toxicity, low flammability as well as no weak C-Cl bonds.

20. ALTERNATIVE TO CFCs Hydrocarbons i.e. C3H8 (flammable, GHG)
2. Hydrochlorofluorocarbons i.e. HClFCs
(still reduce ozone layer, just less)
3. Fluorocarbons i.e. CF4
(almost perfect except act like GHG)
4. Hydrofluorocarbons i.e. CF3CH2F

21. Montreal Protocol effect

22. Montreal Protocol effect

24. QUESTIONS?

29. Marketing of CFCs
1958: DuPont releases CFCs on the market commercially
1971: James Lovelock speculates that CFCs put into the atmosphere may still be present
1973: Mario Molina and F. Sherry Roland start to investigate

30. Original Research
1974: Rowland and Molina C Cl F Cl F C
UV radiation

31. In the news… 1974: Molina and Rowland publish their
hypothesis in Nature.
New York Times runs front page
DuPont responds with study showing that CFCs in troposphere are benign

32. Scientific Controversies
1982: British science teams in Antarctica observe 20% decline in O3 layer
US scientists relying on TOMS (Total Ozone Mapping Spectrometer) measurements from space claim to observe nothing

33. Scientific Evidence
1983: British scientists observe 30% reduction in ozone layer.
US scientists claims no reduction.
1985: British observe 50% reduction.
US claims no reduction.
US re-tests and confirms.
WHY THE SCIENTIFIC CONTRDICTION??

34. Total ozone

35. One step back… 1995: Congress challenges ozone science:
Junk science gains credibility
despite scientific consensus of anthropogenic causes of O3 depletion
1996: Ban begins but black market for CFCs appear