1. OZONE DEPLETION
Ayşe Melis AYGAR
12/D 1261

2. Ozone (O3) ; is a component of the stratosphere
is a very pale bluish gas
has an acrid odor
is very reactive (a powerful oxidizing agent)
has harmful effects on living matter
yet, it is essential to life and health by its presence in the ozone layer
The ozone layer is about 15 to 45 km above the Earth’s surface and holds much of the airs ozone.

3. 2 extremely reactive oxygen atoms Extremely reactive oxygen atoms
Formation of Ozone
O2 molecule UV
High energy, short wavelength
2 extremely reactive oxygen atoms
Extremely reactive oxygen atoms
O2 molecule
OZONE

4. Depletion of Ozone
Resonance structures of ozone suggest that two π bonding electrons are spread over the entire molecule.
Therefore, the bond order of ozone is between a single and a double bond.
This means that ozone molecules can be broken easier than oxygen molecules.

5. When O3 absorbs rather longer wavelength uv light of less energy, the reverse reaction takes place;
O3(g)
O2(g)
Oxygen free radical
O3(g)
2O2(g)
Oxygen free radical

6. Thus, ozone is constantly being formed and broken down
Thus, ozone is constantly being formed and broken down. The ozone layer acts as a shield by absorbing 99% of the sun’s harmful uv light of longer wavelength than that absorbed by O2 and N2.

7. Satellite data shows a clear decline over the last 30 years in ozone concentration in the latitudes 60o south to 60o north. Satellite measurements also show the greatest destruction of the ozone layer at south pole
View of the South Pole from NASA's TOMS (Total Ozone Mapping Spectrometer) satellite. Blue and green indicate relatively large amounts of ozone. Red and yellow mark the "ozone hole," an area of decreased ozone.

8. CFCs, chlorofluorocarbons (freons)
are used in spray cans, old refrigerators, old air conditioners, fire extinguishers
are chemically very inert
do not decompose but float slowly through the atmosphere into the stratosphere

9. Depletion of Ozone by CFCsUV
CCl2F2
CClF2
Cl free radical O2 O3
ClO
Cl free radical O2
O free radical
Cl free radical
ClO

10. Depletion of Ozone by CFCs

11. CF2Cl2 in stratosphere

12. Nitric Oxide
is formed from the high temperature reaction of N2 and O2 in aircraft engines.
Serves as a catalyst during the reaction between O3 and oxygen free radical. NO O3
NO2 O2
NO2
O radical NO O2

13. More sunburn and damage to animals
O3 concentration in stratosphere decreases
More UV light reaches the Earth
More sunburn and damage to animals
Increase in skin cancer and eye cataract cases
Suppression of plant growth
Genetic mutations
Changes in world’s climate

14. Alternatives to CFCs
CFCs are used because of their lack of reactivity, low toxicity and low flammability.
Alternatives to CFCs must have similar properties but with no C-Cl bonds and with little absorption of infrared radiation (in order not to behave like greenhouse gases)

15. Hydrochlorofluorocarbons
Alternatives to CFCs
Hydrochlorofluorocarbons
(HClFCs)
Hydrocarbons
are used as refrigerant coolants.
do not lead to ozone depletion
but are flammable and greenhouse gases
Would lead to global warming
Decompose less easily (have stronger C-H bonds than C-Cl bonds)
Nonetheless, these still can reduce ozone layer
can be a temporary solution only

16. Alternatives to CFCs Fluorocarbons Hydrofluorocarbons
have low reactivity
are non-toxic and not flammable
are stable to UV radiation (presence of strong C-F bond), do not deplete ozone layer
however these are greenhouse gases
do not have any chlorine atoms that can cause ozone depletion
low reactivity, low toxicity and low flammability
However, these contribute to global warming