International Ozone Day is presented to discuss the ozone layer and the threats to it. The ozone layer protects life on Earth by absorbing ultraviolet radiation from the sun. Chlorofluorocarbons (CFCs) released into the atmosphere were depleting the ozone layer. This led to the discovery of the ozone hole over Antarctica in 1985. In response, the Montreal Protocol was established in 1987 to phase out the production of ozone-depleting substances and allow the ozone layer to recover by 2050 to 2075.

1. International Ozone Day
Presented by
Sahil Abbas
B.Tech (CSE)

2. Content
• Ozone
• Dobson Units
• Ozone layer
• Ozone Distribution in the Atmosphere
• CFCs: Ozone Depleting Substances
• Ultra-Violet Radiation
• The Ozone Hole
• Antarctic Ozone Hole
• Montreal Protocol

3. Ozone
• Ozone is a molecule
consisting of oxygen
atoms.
• Ozone gas can be
created or destroyed by
the sun’s UltraViolet
rays as shown in the
picture to the right.

4. Ozone is…
• Ozone is highly
corrosive and toxic
and is used as a
disinfectant.
• It can be found in
small concentrations
in the troposphere
where it is considered
a pollutant.

5. Dobson Units
• Ozone levels are
reported in Dobson
Units (DU).
• 300 DU is an average
value.

6. What is the ozone layer?
The ozone layer is a layer
of gas consisting of O3
molecules, called ozone,
that forms when free
Oxygen molecules bond to
O2 molecules

7. Where is the ozone layer?
• The ozone layer is a
protective layer of gas
molecules located
within the stratosphere.
• Ozone gas also exists in
the troposphere and at
ground level, but most
is located within the
stratospheric layer
shown to the right.

8. Earth’s Atmosphere

9. Ozone Distribution in the Atmosphere

10. Why Protect the Ozone Layer?
• Ozone Depletion leads to excessive UV-B
radiation.
• Excessive UV-B radiation leads to:
– More skin cancers and eye cataracts.
– Less productivity of plants.
– Loss of immunity to diseases.
– Adverse effects on plastics.

11. CFCs: Ozone Depleting Substances
1928: CFCs invented;
1950-70s: Consumption and use of
CFCs rises rapidly during the
50s-70s period. Used in
Aerosols, Refrigeration, Air
Conditioning and
Manufacturing of Foams.

12. CFCs and Ozone

13. And the effects of all those CFCs...

14. Ultra-Violet Radiation
UV rays penetrate the
Earth’s atmosphere at 3
slightly different
wavelengths called
• UV-A
• UV-B and
• UV-C rays.

15. So, why is the ozone layer
important to life on Earth?
• The stratospheric ozone
layer completely stops
the penetration of UV-C
rays and eliminates
most of the UV-B rays.
• Therefore, the ozone
layer protects life on
Earth from the harmful
effects of solar radiation
on a daily basis.

16. How are we as humans affecting
the ozone layer?
• Since 1928, Chlorofluorocarbons have been
produced, originally as nonflammable
refrigerants for use in refrigerators, and
eventually for use in fire extinguishers, dry
cleaning agents, pesticides, degreasers,
adhesives, and as propellants for aerosol
products.
• As these CFCs have been released into the
atmosphere, the level of ozone in the
stratosphere has decreased.
• CFCs have an estimated lifespan of more than
100 years.

17. Before and with Ozone hole

18. The Ozone Hole
• Since the 1970’s the ozone hole has been
increasing in size over the Antarctic.
• For the first time, in September of 2000, the
ozone hole became so large it actually left
populated areas of southern Chile fully
exposed to the effects of the Sun’s UV rays.

19. Chile’s Ozone Hole

20. How does ozone depletion
affect global warming and
ultimately climate change?
• As ozone levels in the stratosphere are
depleted, more solar radiation penetrates the
Earth’s atmosphere.
• This affect results in an increase in solar
radiation reaching the Earth’s surface adding
to an increase in surface temperature.
• In turn, global warming actually results in a
warming of the troposphere, but a cooling of
the stratosphere, hindering the ozone layer’s
natural chemistry for repairs.

21. Antarctic 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.
The Ozone Hole has
steadily grown in size (up
to 27 million sq. km.) and
length of existence (from
August through early
December) over the past
two decades.

22. What is the Montreal Protocol?
• The Montreal Protocol is a landmark
international agreement designed to
protect the stratospheric ozone
layer.
• 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.

23. The Ozone Hole in October
1980 1985 1990 1996
2000 2005

24. Total Ozone Reanalysis

25. So what are we doing about it?
• After the discovery of ozone depletion in the late 1970’s, many countries
agreed that something must be done worldwide to stop the production of
man-made, ozone harmful products.
• The international community adopted the Vienna Convention in 1985
followed by the Montreal Protocol in 1987.
• The latest reports confirm that it has led to the phasing out of about 95%
of the consumption of ozone-depleting substances (ODS) listed in the
agreement. In turn, this has led to the prospect of the ozone layer
recovering by 2050 to 2075.
• Furthermore, the phasing out of ozone-depleting substances has helped
to fight climate change since many of these chemicals are also powerful
greenhouse gases. According to a recent study, the phasing out of
substances under the Protocol led to more reductions in greenhouse gases
than what is foreseen under the Kyoto Protocol.