The ozone hole was first discovered in 1985 by British physicist Joe Farman. It is caused by chlorofluorocarbons (CFCs) emitted from industries that react with ozone in the stratosphere. CFCs contain chlorine atoms that break down ozone molecules. The conditions in Antarctica, including its long winter darkness and polar stratospheric clouds, allow chlorine to accumulate and destroy large amounts of ozone each spring, depleting the ozone layer over Antarctica and forming the ozone hole.

1. Presented by:
Hira Sumbal (15)
Aarfa Tufail (11)
Nawal Khalid (25)
shereen Rehman (31)
Ozone hole

2. “It is a naturally
occurring layer in
stratosphere extended
from 15 to 30 km
above the Earth
protecting from
ultraviolet radiation
which damage the life
on earth.”
Ozone Layer

3. “The thinning of ozone layer in stratosphere over
Antarctic due to ozone layer depletion caused by
several anthropogenic processes is called ozone
hole.
Ozone hole

4. This phenomena was first discovered by Joe
Farman, a British physicist in in May 1985.
 the study of Farman and his colleagues reveals
that the levels of ozone over Antarctica has fallen
40% between 1975 and 1984
They demonstrated that the hole was not a
natural occurrence but the result of reactions
triggered by chlorofluorocarbons (CFCs) in the
stratosphere.
Discovery of Ozone hole

5.  CFCs contains chlorine, fluorine and carbon
atoms.
They are emitted from industries, refrigerator, air
conditioner, aerosols etc.
1 million tones of CFCs are released annually.
Major constituent in ozone depletion
Once free, the CFCs float up to the ozone layer and
remain there for 75 to 100 years, destroying the
ozone molecules.
CFCs

6. Factors:
(1)Polar vertex.
(2)Polar Stratospheric clouds.
(3)Effect of active chlorine.
These are factors which
triggers the formation of ozone
hole over Antarctica.
Why ozone hole is only formed over
Antarctica?

7. Polar vertex is one of the major reason of ozone
hole. During winter season in Antarctica, strong
wind blows in continent called polar vertex-this
isolates the air over Antarctic from rest of the world.
Why ozone hole is only formed over
Antarctica?

8. For rapid ozone destruction, stratospheric clouds have
to form in ozone layer. These clouds are only formed
in Antarctic where winter is cold enough for these
clouds to form widely through the centre of the ozone
layer.
Why ozone hole is only formed over
Antarctica?

9. Polar vertex-cold circulating wind,
formation of stratospheric clouds and 6
months of darkness over Antarctic, all
provide ideal conditions for chlorine to
break from the CFCs. This active chlorine,
bromine and other ozone depleting
substances destroys the ozone 1% per
day during spring causing the formation
of ozone hole.
Why ozone hole is only formed over
Antarctica?

10.  One chlorine atom is capable of fragmentation of 1,000 to
10,000 to 1 million of ozone molecules.
Why ozone hole is only formed over
Antarctica?

11. The concentration of ozone in the atmosphere is measured in
"Dobson Units", the average concentration of ozone in the
atmosphere is about 300 Dobson Units. The ozone hole is considered
to be wherever the concentration drops below 220 Dobson Units.
 Ozone layer depletion over Antarctic during summer season
Why ozone hole is only formed over Antarctica?

12. Recent research has shown that chlorine monoxide can
react with stratospheric nitrogen dioxide to form chlorine
nitrate (ClONO2). When chlorine nitrate is in the presence
of trace amounts of HCl or absorbed on ice particles in
stratospheric clouds, additional redox reactions can occur
in which chlorine nitrate produce Cl2 or HOCl.
HCl(g) + ClONO2(g) Cl2(g) + HNO3
H2O(g) + ClONO2(g) HOCl(g) + HNO3(g)
Why ozone hole is only formed over
Antarctica?

13. Both Cl2 and HOCl undergo cleavage reactions by even
weak sunlight to give reactive chlorine atoms. When the
sun finally rises after the long polar night, relatively large
amounts of Cl2 and HOCl are present and rapidly generate
high levels of chlorine atoms.
HCl(g) + ClONO2(g) Cl2(g) + HNO3
H2O(g) + ClONO2(g) HOCl(g) + HNO3(g)
Why ozone hole is only formed over
Antarctica?