1. OZONE LAYER
DEPLETION
1

2. WHAT IS OZONE?
 Ozone is a form of oxygen with 3
oxygen atoms (O3).
2

3. How is ozone produced?
It is formed when oxygen absorbs solar
radiation - O2 +h(<240nm)  O+O
O+ O2  O3
3

4. 4

5. OZONE LAYER
• Ozone is a triatomic form of oxygen (O3)
found in Earth’s upper and lower
atmosphere.
• The ozone layer, is situated in the
stratosphere about 15 to 30 km above the
earth's surface.
5

6. 6

7. Ozone (parts per million)
0
20
40
60
80
100
Altitude
(km)
Troposphere
Mesosphere
Thermosphere
Ozone Facts
Altitude
(miles)
10
0
20
30
40
50
60
90% of ozone is in the
stratosphere
0 2 4 6 8
10% of ozone is in the troposphere
7
The amount of ozone within the stratosphere
varies according to altitude

8. Why is the ozone layer important
• Ozone acts as the Earth’s protective
shield against the Sun’s harmful
Ultraviolet radiation (UV radiation).
• Without the ozone layer, life would not
exist on Earth!
8

9. Why life would not exist?
Exposure to Ultraviolet rays results into;
• Sunburn (or erythema) is redness of the skin,
which is due to increased blood flow in the skin
caused by dilatation of the superficial blood
vessels in the dermis as a result of exposure to
UV radiation
• Tanning refers to delayed pigmentation of the
skin, or melanin pigmentation. It usually
becomes noticeable one to two days after
exposure to the sun and gradually increases for
several days persisting for weeks or months.
9

10. Why life would not exist?
• Premature Aging of the Skin
One of the chronic effects resulting from
repeated exposure to UV radiation is premature
aging of the skin, which encompasses a number
of clinical signs that reflect structural changes in
the dermis. These clinical signs include dryness,
wrinkles
10

11. Why life would not exist?
• Suppression of the Immune System
Suppression of the immune system resulting
from exposure to UV radiation is believed to be
an important contributor to the development of
nonmelanoma skin cancers.
• Damage to the Eyes
UV rays can also damage the eyes as more than
99% of UV radiation is absorbed by the front of
the eyes.
11

12. Why life would not exist?
Corneal damage, cataracts, and macular
degeneration are all possible chronic effects
from UV exposure and can ultimately lead to
blindness
• Skin Cancer
Skin cancers are the most commonly occurring
cancers in terms of incidence in the world.
12

13. UV radiation
• UV radiation is emitted from the sun with
wavelength from 200-400 nm
(nanometers)
• UV radiation is divided into three ranges
▫ UV-A, 320 - 400 nm
▫ UV-B, 290 - 320 nm
▫ UV-C, 200 - 290 nm
• The shorter wavelength are more harmful
to biological life.
13

14. OZONE LAYER DEPLETION
• The Ozone layer depletion is caused by
chemicals called CFCs
(chlorofluorocarbons). CFCs escape
into the atmosphere from refrigeration
and propellant devices and processes,
and they are so stable they last for
decades.
• This long life allows some CFCs to
eventually reach the stratosphere.
14

15. • The chemicals that make up CFCs,
mainly chlorine and fluorine, float
around the stratosphere, breaking up
ozone molecules.
• One molecule of CFC can destroy more
than 100,000 molecules of
stratospheric ozone.
15

16. The ozone depletion process
16

17. Destruction of ozone by chlorine
17

18. Chemical reactions
• CCl3F + UV Light => CCl2F + Cl
• CCl2F2 + UV Light => CClF2 + Cl
• The chlorine atoms formed in the
above reactions readily depletes ozone
via a chain reaction:
• Cl + O3 => ClO + O2
• ClO + O => Cl + O2
18

19. The important catalysts for
stratospheric O3 destruction
• Hydroxy radical (OH)
.OH + O3 = HO2
. + O2
HO2
. + O = .OH + O2
Net: O + O3 = 2 O2
• Chlorine and bromine (Cl and Br)
Cl. + O3 = ClO. + O2
ClO. + O = Cl. + O2
Net: O + O3 = 2 O2
• Nitric oxide (NO)
NO + O3 = NO2 + O2
NO2 + O = NO + O2
Net: O + O3 = 2 O2
HOx cycle
ClOx cycle
NOx cycle
19

20. 20

21. Ozone Depleting Substances
• Chlorofluorocarbons (CFC’s)
▫ Contains: Cl, F, C
▫ Long-lived, non-toxic, non-corrosive,
and non-flammable
▫ In 1960’s used in refrigerators, air
conditioners, spray cans, solvents,
foams
▫ Phased out in 1996 in developed
countries
21

22. • Hydrochlorofluorocarbons
(HCFCs)
▫ Contains: H, Cl, F, C
▫ First major replacement for CFC
▫ Much less destructive but also ozone
depleting
▫ Reduce HCFC’s by 35% in 2004 in
developed countries
22

23. • Halons
▫ Contain: Br, Cl (in some but not all),
F, H (in some but not all), C
▫ Br many times more effective in
destroying O3
▫ Halons used in fire extinguishers
▫ Phased out in 1994
23

24. • Methyl Bromide (CH3Br)
▫ an effective pesticide, used to
fumigate e.g. soil and products
24

25. Breakdown of Sources
Sterilization
3%
Aerosols
5%
Refrigeration
and Air
Conditioning
30%
Other Products
1
2%
Solvent Cleaning
Products
36%
Foam Products
1
4%
25

26. Responsibility for ozone damage each
year
26

27. OZONE HOLE
The ozone hole is a region of
depleted ozone in the stratosphere
over the Antarctic that happens at the
beginning of Southern Hemisphere
spring
27

28. WHERE IS THE OZONE HOLE?
Ozone hole largely restricted to areas over
Antarctica
Ozone hole may pass over tip of South
America
Ozone hole seldom comes near Australia.
28

29. Who discovered the Ozone Hole?
• The Antarctic Ozone Hole was
discovered in 1985 by British scientists
Joseph Farman, Brian Gardiner, and
Jonathan Shanklin of the British
Antarctic Survey.
29

30. September 2006
© NASA
30

31. Monthly averages for October
31

32. EFFECT OF OZONE LAYER
32

33. Why Protect the Ozone Layer?
• Ozone Depletion leads to excessive UV-B
radiation.
• Excessive UV-B radiation leads to:
▫ More skin cancers
▫ Eye cataracts.
▫ Less productivity of plants.
▫ Loss of immunity to diseases.
▫ Adverse effects on plastics.
▫ Damage to ocean eco-ecosystems
33

34. PROTECTING THE OZONE LAYER
• Ban the use of CFC’s
Have to replace with something
Current replacements are greenhouse
gases and do not eliminate ozone
depletion, just slow it down
• Air Quality Standards
Limit amounts of pollutants that can be
emitted by pollution sources
34

35. What is being done about ozone
depletion?
 Montreal Protocol (1987): international
agreement designed to protect
the stratospheric ozone layer
by phasing out ozone depleting
chemicals
35

36. What is the Montreal Protocol?
• The Montreal Protocol says that the
production and consumption of
compounds that deplete ozone in the
stratosphere--chlorofluorocarbons (CFCs),
halons, carbon tetrachloride, and methyl
chloroform--are to be phased out by 2030.
36

37. 37
Montreal Protocol
• Vienna Convention in 1985
▫ framework agreement
• Montreal Protocol in 1987
▫ Phase-out schedules for CFCs and
halons

38. • London Amendment in 1990
▫ accelerated phase outs; additional
CFC’s, CCl4, CH3CCl3
• Copenhagen Amendment in 1992
▫ added methyl bromide, HBFCs,
HCFCs
• Montreal Amendment in 1997
▫ finalized phase-out schedules for
methyl bromide
38

39. Efforts Need to Be Continued
• Create reliable models
▫ To gain a better understanding of the
effects ozone depletion has on organisms
living within different ecosystems
• Enforcement of Montreal Protocol
▫ To reduce concentrations of chemicals
responsible for ozone depletion
...
39

40. • Monitoring chemicals being emitted
• Gain a better overall understanding on just
how ozone depletion is affecting our
planet
40

41. Montreal Protocol
Summary of Montreal Protocol control measures
Ozone depleting substances Developed countries Developing countries
Chlorofluorocarbons (CFCs) Phased out end of 1995a Total phase out by 2010
Halons Phased out end of 1993 Total phase out by 2010
Carbon tetrachloride Phased out end of 1995a Total phase out by 2010
Methyl chloroform Phased out end of 1995a Total phase out by 2015
Hydrochlorofluorocarbons (HCFCs) Freeze from beginning of 1996b
35% reduction by 2004
75% reduction by 2010
90% reduction by 2015
Total phase out by 2020c
Freeze in 2013 at a base level
calculated as
the average of 2009 and 2010
consumption levels
10% reduction by 2015
35% reduction by 2020
67.5% reduction by 2025
Total phase out by 2030d
Hydrobromofluorocarbons (HBFCs) Phased out end of 1995 Phased out end of 1995
Methyl bromide
(horticultural uses)
Freeze in 1995 at 1991 base levele
25% reduction by 1999
50% reduction by 2001
70% reduction by 2003
Total phase out by 2005
Freeze in 2002 at average 1995-1998
base levele
20% reduction by 2005
Total phase out by 2015
Bromochloromethane (BCM) Phase out by 2002 Phase out by 2002
41

42. Recovery of Ozone Layer
• Since the adoption and strengthening
of the Montreal Protocol has led to
reductions in the emissions of CFCs,
atmospheric concentrations of the
most significant compounds have
been declining. These substances are
being gradually removed from the
atmosphere.
42

43. • By 2015, the Antarctic ozone hole
would be reduced by only 1 million
km² out of 25
• Complete recovery of the Antarctic
ozone layer will not occur until the
year 2050 or later.
43

44. Signs of Recovery???
There have been some signs of recovery
▫ 1997 satellite showed a decline of
several known ozone-depleting
gases
▫ Satellite images show some slowing
down of ozone loss
However recovery is slow….
44

45. Images of Antarctica Taken Indicate A Slow
Recovery
45