The document discusses ozone depletion and the formation of the ozone layer. It describes how CFCs released from products like aerosol sprays were transported to the stratosphere and destroyed ozone. This led to a 4% decline in total ozone annually and the development of a seasonal ozone hole over Antarctica. International agreements like the Montreal Protocol were implemented to phase out CFCs and ozone-depleting substances. Adherence to these treaties is expected to allow the ozone layer to recover by 2050.

1. 3.6.2 Global Climatic Change
IB Geography
Climatic Hazards and Change
Ozone depletion in the
stratosphere

2. Syllabus Objective
1.Be aware of the factors responsible for the formation
of stratospheric ozone and its depletion by atmospheric
pollution and natural causes.
2.Understand the effects of ozone depletion on humans,
animals and plants. Study local, national and international
responses to ozone depletion.

3. What is Ozone?
Ozone or trioxygen (O3)
is a triatomic molecule,
consisting of three oxygen
atoms.

4. What is the Ozone Layer
The ozone layer is a layer 15 - 30 kms up in Earth's atmosphere
which contains relatively high concentrations of ozone (O3).
( somewhere in the neighborhood of 0.00006% of the atmosphere)
This layer absorbs 93-99% of the sun's high frequency ultraviolet
light, (UV-B) which is potentially damaging to life on earth.

5. Effects on marine ecosystems
UV-B can penetrate clear water to a depth of 20 metres.
There is recent evidence that exposure to enhanced UV-B is
harmful to phytoplankton, plankton and the larvae of fish and
shrimps.

6. Effects on plants
Although plants can react to UV-B by changing their pigment
or growing in shaded positions, prolonged exposure may
cause serious damage. Resistance to disease could be reduced
and so lead to lower crop yields. Some temperate crops such
as peas and cabbage are particularly sensitive. Failure of crops
or even reduced cover leaves soils more prone to erosion.

7. Effects on human health
Although humans have natural defences against ultra-violet
radiation, prolonged exposure to UV-B can have serious
effects on human health. Skin, if not protected can experience
sunburn. Prolonged exposure can lead to the immune
defences of the skin breaking down. This may lead to an
increased susceptibility to infection, premature ageing of skin,
and skin disorders.

8. How is Ozone formed
Ozone in the stratosphere is mostly produced from ultraviolet
rays reacting with oxygen:
O2 + photon(radiation< 240 nm) → 2 O
O + O2 → O3

9. How is Ozone destroyed?
It is destroyed by reaction with atomic oxygen:
O3 + O → 2 O2
The latter reaction is catalysed by the presence of certain
free radicals, of which the most important are hydroxyl
(OH), nitric oxide (NO) and atomic chlorine (Cl) and
bromine (Br).

10. Ozone depletion
Ozone depletion describes two distinct, but related
observations:
• a slow, steady decline of about 4 percent per decade in the
total amount of ozone in Earth's stratosphere since the late
1970s;
• and a much larger, but seasonal, decrease in stratospheric
ozone over Earth's polar regions during the same period. The
latter phenomenon is commonly referred to as the ozone
hole.

11. Human Contributions to Ozone
destruction
Scientists suspected that a range of man-made gases, such as
chlorofluorocarbons (CFCs), might be responsible for ozone
depletion. CFCs were used in fridges, air-conditioning units,
plastic foams and aerosol sprays.
These gases are transported high into the stratosphere
where they are eventually broken down by UV radiation. This
reaction releases free chlorine, which acts as a catalyst in the
destruction of ozone.

13. Antarctic Ozone Hole
An area of the Antarctic stratosphere
in which the recent ozone levels have
dropped to as low as 33% of their
pre-1975 values. The ozone hole
occurs during the Antarctic spring,
from September to early December, as
strong westerly winds start to
circulate around the continent and
create an atmospheric container

14. Ozone depletion
Ozone depletion describes two distinct, but related
observations:
• a slow, steady decline of about 4 percent per decade in the
total amount of ozone in Earth's stratosphere since the late
1970s;
• and a much larger, but seasonal, decrease in stratospheric
ozone over Earth's polar regions during the same period. The
latter phenomenon is commonly referred to as the ozone
hole.

15. Study local responses to ozone
depletion
Ozone depletion describes two distinct, but related
observations: a slow, steady decline of about 4 percent per
decade in the total amount of ozone in Earth's stratosphere
since the late 1970s; and a much larger, but seasonal, decrease
in stratospheric ozone over Earth's polar regions during the
same period. The latter phenomenon is commonly referred to
as the ozone hole.

16. Study national responses to ozone
depletion

17. Study national responses to ozone
depletion
banning or
phasing out of

18. Study national responses to ozone
depletion

19. Study national responses to ozone
depletion
Cooling technology that uses “freon”
older fridges & A/C

20. Study national responses to ozone
depletion
Cooling technology that uses “freon” Hairspray
older fridges & A/C that uses CFCs

21. Study national responses to ozone
depletion
Cooling technology that uses “freon”
older fridges & A/C

22. Study national responses to ozone
depletion
Cooling technology that uses “freon”
older fridges & A/C
Not “Hairspray”
the Musical

23. Study international responses to ozone
depletion
Montreal Protocol
Kyoto Protocol

24. Study international responses to ozone
depletion
1976 - U.S. National Academy of Sciences says credible evidence of ozone depletion, - Halocarbon
Industry skeptical
1983 - New leadership in USA EPA pushes for an international approach to halocarbon regulations.
1985 - 20 nations, including most of the major CFC producers, signed the Vienna Convention which
established a framework for negotiating international regulations on ozone-depleting substances.
That same year, the discovery of the Antarctic ozone hole was announced, causing a revival in public
attention to the issue.
1987 - Montreal Protocol signed. Meanwhile, the halocarbon industry shifted its position and
started supporting a protocol to limit CFC production. The reasons for this '...the chemical industry
supported the Montreal Protocol in 1987 because it set up a worldwide schedule for phasing out
CFCs, which [were] no longer protected by patents. This provided companies with
an equal opportunity to market new, more profitable compounds.'

25. The Montreal Protocol on Substances
That Deplete the Ozone Layer
An international treaty designed to protect the ozone layer by
phasing out the production of a number of substances believed to
be responsible for ozone depletion. It is believed that if the
international agreement is adhered to, the ozone layer is expected
to recover by 2050. Due to its widespread adoption and
implementation it has been hailed as an example of exceptional
international co-operation with Kofi Annan quoted as saying it is
quot;Perhaps the single most successful international
agreement to date has been the Montreal Protocolquot;.

26. Kyoto Treaty
An international treaty designed to protect the ozone layer by
phasing out the production of a number of substances believed to
be responsible for

27. The highest levels of ozone in the atmosphere are in the stratosphere, in a
region also known as the ozone layer between about 10 km and 50 km
above the surface (or between 6.21 and 31.1 miles). Here it filters out
photons with shorter wavelengths (less than 320 nm) of ultraviolet light,
also called UV rays, (270 to 400 nm) from the Sun that would be harmful
to most forms of life in large doses. These same wavelengths are also
among those responsible for the production of vitamin D, which is
essential for human health. Ozone in the stratosphere is mostly produced
from ultraviolet rays reacting with oxygen