2. What is Ozone layer?
• It is a natural sunscreen in the stratosphere
• It filters out harmful ultraviolet radiations from the sunlight &
thereby protects various life forms on the earth.
• It is a form of oxygen; ozone is continously being created by the
absorption of short wave length UV radiations in the stratosphere.
• Ozone is a poisonous gas made up of molecules consisting of
three oxygen atoms.
• The ozone layer effectively blocks almost all solar radiation of
wavelengths less than 290 nanometres from reaching Earth’s
surface, including certain types of ultraviolet (UV) and other forms
of radiation that could injure or kill most living things.
• The amount of ozone in the stratosphere varies naturally
throughout the year as a result of chemical processes that create
and destroy ozone molecules and as a result of winds and other
transport processes that move ozone molecules around the
planet.
3.
4. • While stratospheric ozone which protects us from
the sun is good, there is also ozone produced near
the ground from sunlight interacting with
atmospheric pollution in cities that is bad for human
health.
• It causes breathing problems for some people, and
usually occurs in the summertime when the pollution
over a city builds up during stagnant air conditions
associated with high pressure areas.
• The ozone layer above Antarctica will not return to
its early 1980s state until about 2060, according to
Nasa
The ozone hole reached its maximum size on
September 22, covering 8.2 million square miles
(21.2 million square kilometers), or the area of the
United States, Canada and Mexico combined.
The average size of the 2012 ozone hole was 6.9
million square miles (17.9 million square
kilometers).
The September 6, 2000 ozone hole was the largest
on record at 11.5 million square miles (29.9 million
square kilometers).
5. The Chapman Cycle
• The stratosphere is in a constant cycle with oxygen molecules
and their interaction with ultraviolet rays.
• This process is deemed a cycle because of its constant conversion
between different molecules of oxygen.
1. An oxygen molecules is photolyzed by solar radiation,
creating two oxygen radicals:
hv + O2 → 2O.
2. Oxygen radicals then react with molecular oxygen to produce
ozone:
O2 + O. → O3
3. Ozone then reacts with an additional oxygen radical to form
molecular oxygen:
O3 + O. → 2O2
4.Ozone can also be recycled into molecular oxygen by reacting
with a photon:
O3 + hv → O + O.
6. Thinning of Ozone layer
• The Antartic ozone hole was discovered by Dr Joe C. Farman & his
colleagues.
• Steep decline has been observed since mid 1970s with a record
low concentration of 90 DU in early October of 1993.
• The main reason for Ozone depletion is due to
Chlorofluorocarbons (CFC).
• CFCs are used as coolants in refrigerators & air conditioners, as
propellants, cleaning solvents, sterilant, etc.
• CFCs released in the troposphere reach the stratosphere & remain
there for 65-110 years destroying O₃ molecules.
• In 1985, scientists discovered that 50%(98% in some areas) of
upper stratospheric ozone over Antartica was destroyed during
the antartica’s spring & early summer.
• Nitrous oxide emitted by supersonic aircrafts, during combustion
of fossil fuel and use of nitrogen fertilizers & CFCs breaks ozone
molecules.
7.
8.
9. Contd….
Chemistry of Ozone Depletion
• CFC molecules are made up of chlorine, fluorine and carbon
atoms and are extremely stable.
• This extreme stability allows CFC's to slowly make there way into
the stratosphere.
• This prolonged life in the atmosphere allows them to reach great
altitudes when photons are more energetic.
• The following reaction displays how Cl atoms have an ozone
destroying cycle:
Cl + O3 → ClO + O2
ClO + O → Cl + O2
________________
O3 + O → 2O2 : Overall reaction
10. Effects of Ozone
depletion
• Ozone depletion in the
sratosphere will result in more UV
radiation reaching the earth
especially UV-B(290-320nm)
affecting DNA & photosynthetic
reactions causing skin cancer.
• Easy absorption of UV rays by
the lens & cornea of eye will
result in increase in incidents of
cataract.
• Melanin producing cells of
epidermis will be destroyed by UV
–rays resulting in immuno-
suppression.
• Fair people will be at a greater
risk of UV exposure.
• Phytoplanktons are sensitive to
UV exposure.
• Yield of vital crops like corn,
rice, soyabean, cotton, bean, pea,
sorghum & wheat will decrease.
• Degradation of paints, plastics 7
other polymers will result in
economic loss.
11. Initiatives against the depletion of the
ozone layer
Inter- governmental negotiations for an
international agreement to phase out ozone-
depleting substances started in 1981.
In may 1985, British scientists published their
discovery of severe ozane depletion over the
Antarctic.
The discovery of the ozone ‘hole’ shocked the
world.
It is regarded as one of the major environmental
disasters of 20th Century.
12.
13. Cont..
The governments now recognized the need for
stronger measures to reduce the production and
consumption of a number of CFCs and several
halons.
As a result, the Montreal protocol on sustances
that Deplete the ozane layer was adopted in
september 1987.
In 2009 the Montreal Protocol became the first
UN treaty to achieve universal ratification(that is,
by all the member countries), demonstrating the
world’s commitment to ozone protection, and
more broadly, to global environment
conservation.
14. Results So far…?
As of the end of 2009, the parties to the protocol
had phased out the consumption of 98% of all
the chemicals controlled by the protocol.
There was strong evidence that global ODS
concentrations were decreasing and that the
global stratosphere had already experienced its
highest levels of ozone depletion from man-made
halocarbons.
Outside the polar regions the ozone layer has
shown some initial signs of recovery.
Arctic ozone levels are expected to return to pre
1980 levels before 2050, while Antarctic ozone is
expected to do so in 2060-2075.
15. Cont..
It is estimated that without the protocol, by the
year 2050 ozone depletion would have risen to at
least 50% in the northern hemisphere’s mid
latitudes and 70% in the southern mid latitudes,
about 10 times worse than current levels.
The implications of this would have been
horrendous, and have been estimated to include:
20 million more cases of cancer, and 130 million
more cases of eye cataracts, if there had been no
Montreal Protocol.
Ozone depleting substances are also potent
greenhouse gases, the protocol has delivered
substantial climate benefits too.
16. Montreal protocol
The efforts of the world community to protect the
ozone layer are a fascinating example of how
humanity can act as one to face a common
danger.
• Ensure that improved scientific understanding can
be incorporated quickly into decisions about the
provisions of the treaty.
• Promote universal participation by recognizing
the ‘common but differentiated responsibility’ of
developing and developed countries and ensuring
the necessary financial and technogical support to
developing countries.
