2. Learning objective:-
• Introduction
• Ozone Layer
• Formation of Ozone
• Ozone layer depletion
• Ozone layer depletion substance
• Impacts of Ozone Layer Depletion
• Measures to prevent the ozone layer depletion
• Conclusion
• Reference
3. Introduction
• In 1969 Dutch chemist Paul Crutzen published a paper that described the major nitrogen oxide
catalytic cycle affecting ozone levels. Crutzen demonstrated that nitrogen oxides can react with
free oxygen atoms, thus slowing the creation of ozone (O3), and can also decompose ozone into
nitrogen dioxide (NO2) and oxygen gas (O2).
• In 1974, American chemists Mario Molina and F. Sherwood Rowland of the University of
California at Irvine recognized that human-produced chlorofluorocarbons (CFCs)—molecules
containing only carbon, fluorine, and chlorine atoms—could be a major source of chlorine in the
stratosphere. They also noted that chlorine could destroy extensive amounts of ozone. One chlorine
can destroy 100,000 molecules of ozone. It is destroyed more quickly than it is created.
• Ozone depletion, gradual thinning of Earth’s ozone layer in the upper atmosphere caused by the
release of chemical compounds containing gaseous chlorine or bromine from industry and other
human activities. The thinning is most pronounced in the polar regions, especially over Antarctica.
• Montreal Protocol was proposed in 1987 to stop the use, production and import of ozone-depleting
substances and minimize their concentration in the atmosphere to protect the ozone layer of the
earth.
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4. Ozone Layer:-
• Ozone (O3) is a highly reactive gas composed of three oxygen atoms. It is both a natural
and a man-made product that occurs in the Earth's upper atmosphere (the stratosphere)
and lower atmosphere (the troposphere). Depending on where it is in the atmosphere,
ozone affects life on Earth in either good or bad ways.
• Stratospheric ozone is formed naturally through the interaction of solar ultraviolet (UV)
radiation with molecular oxygen (O2). The "ozone layer," approximately 10 through 31
miles above the Earth's surface, reduces the amount of harmful UV radiation reaching
the Earth's surface.
• Tropospheric or ground-level ozone – what we breathe – is formed primarily from
photochemical reactions between two major classes of air pollutants, volatile organic
compounds (VOC) and nitrogen oxides (NOx). these pollutants form ozone molecules in
the presence of sunlight.
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6. Formation of Ozone
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Stratospheric ozone Stratospheric ozone is formed when solar energetic ultraviolet (UV) radiation dissociates molecules of
oxygen, O2, into separate oxygen atoms. Free oxygen atoms can recombine to form oxygen molecules
but if a free oxygen atom collides with an oxygen molecule, it joins up, forming ozone.
Creation
• An oxygen molecule is split (photolyzed) by higher frequency UV light (top end of UV-B, UV-C and above) into two
oxygen atoms.
O2 + ℎν(<242 nm) → 2 O.
• Each oxygen atom then quickly combines with an oxygen molecule to form an ozone molecule:
O + O2 → O3
The ozone–oxygen cycle
• The ozone molecules formed by the reaction above absorb radiation having an appropriate wavelength between UV-C
and UV-B. The triatomic ozone molecule becomes diatomic molecular oxygen plus a free oxygen atom.
O3 + ℎν(240–310 nm) → O2 + O
• The atomic oxygen produced quickly reacts with another oxygen molecule to reform ozone:
O + O2 + A → O3 + A
Removal:
• If an oxygen atom and an ozone molecule meet, they recombine to form two oxygen molecules:
O3 + O → 2 O2
• And if two oxygen atoms meet, they react to form one oxygen molecule:
2 O → O2
7. Formation of Troposhere Ozone
• Tropospheric O3 is considered as the most widespread secondary pollutant and one of the
components of global climate change.
• Tropospheric ozone is formed by the interaction of sunlight, particularly ultraviolet light, with
hydrocarbons and nitrogen oxides, which are emitted by automobile tailpipes and smokestacks. In
urban areas, high ozone levels usually occur during warm summer months.
8. Ozone layer Depletion
• Ozone depletion is a major environmental problem because it increases the amount of ultraviolet
(UV) radiation that reaches Earth’s surface, which increases the rate of skin cancer, eye cataracts,
and genetic and immune system damage.
• Ozone depletion, gradual thinning of Earth’s ozone layer in the upper atmosphere caused by the
release of chemical compounds containing gaseous chlorine or bromine from industry and other
human activities. The thinning is most pronounced in the polar regions, especially over Antarctica.
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11. Ozone layer depletion substances
Ozone depleting substances are chemicals that destroy the earth’s protective ozone layer.
They include:
• Chlorofluorocarbons (CFCs)
• Halons
• Carbon tetrachloride (CCl4)
• Methyl chloroform (CH3CCl3)
• Hydrobromofluorocarbons (HBFCs)
• Hydrochlorofluorocarbons (HCFCs)
• Methyl bromide (CH3Br)
• Bromochloromethane (CH2BrCl)
The use of these chemicals is controlled by the Montreal Protocol on substances that Deplete
the Ozone Layer.
12. Chlorofluorocarbons (CFCs)
• Chlorofluorocarbons (CFCs) are nontoxic, nonflammable chemicals containing atoms of carbon,
chlorine, and fluorine. CFCs are classified as halocarbons, a class of compounds that contain atoms
of carbon and halogen atoms.
• Refrigerators in the late 1800s and early 1900s used the toxic gases, ammonia (NH3), methyl
chloride (CH3Cl), and sulfur dioxide (SO2), as refrigerants. After a series of fatal accidents in the
1920s when methyl chloride leaked out of refrigerators, a search for a less toxic replacement begun
as a collaborative effort of three American corporations- Frigidaire, General Motors, and Du Pont.
• CFCs were first synthesized in 1928 by Thomas Midgley, Jr. of General Motors, as safer chemicals
for refrigerators used in large commercial appilications.
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13. Sources of CFCs:-
• Refrigerators and Air Conditioners.
• Aircraft Halon.
• Aerosol Sprays.
• Rogue CFCs*.
A mysterious spike in emissions of an ozone-destroying gas has been tracked to northeast China,
where scientists suspect that the chemical is being produced and used in violation of international
law.The chemical — trichlorofluoromethane, also known as CFC-11 — was once commonly used in
spray-foam insulation for refrigerators and buildings. CFC-11 is one of the most potent chemicals
responsible for creating the ozone hole in the stratosphere over the Southern Hemisphere.
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15. Halons
• Halon, chemical compound formerly used in firefighting. A halon may be any of a group of
organohalogen compounds containing bromine and fluorine and one or two carbons. The
effectiveness of halons in extinguishing fires arises from their action in interrupting chain reactions
that propagate the combustion process.
• Halons are both atmospheric ozone depleters and greenhouse gases. In accordance with the
Montreal Protocol, their manufacture and consumption were phased out in industrialized nations by
Jan. 1, 2000.
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16. Carbon tetrachloride
• Carbon Tetrachloride is a clear, colorless, volatile and very stable chlorinated hydrocarbon. Carbon
Tetrachloride is used as a solvent for oils and fats, as a refrigerant and as a dry-cleaning agent.
• Inhalation of its vapors can depress central nervous system activity and cause degeneration of the
liver and kidneys. Carbon Tetrachloride is reasonably anticipated to be a human carcinogen based
on evidence of carcinogenicity in experimental animals.
• Carbon tetrachloride is a manufactured chemical that does not occur naturally. It is a clear liquid
with a sweet smell that can be detected at low levels. It is also called carbon chloride, methane
tetrachloride, perchloromethane, tetrachloroethane, or benziform.
• Carbon tetrachloride was originally synthesized by the French chemist Henri Victor Regnault in
1839 by the reaction of chloroform with chlorine, but now it is mainly produced from methane.
• Carbon tetrachloride was also widely used as a precursor to chlorofluorocarbons (CFCs)
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17. Methyl chloroform
• The organic compound 1,1,1-trichloroethane, also known as methyl chloroform, is a chloroalkane.
This colorless, sweet-smelling liquid was once produced industrially in large quantities for use as a
solvent. It is regulated by the Montreal Protocol as an ozone-depleting substance and its use is
being rapidly phased out.
• 1,1,1-trichloroethane appears as a colorless liquid. May irritate skin, eyes and mucous membranes.
In high concentrations the vapors may have a narcotic effect. Nonflammable, but may decompose
and emit toxic chloride fumes if exposed to high temperatures. Used as a solvent.
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18. Hydrobromofluorocarbons
• Hydrobromofluorocarbons (HBFCs) are composed of molecules containing one, two or three
carbon atoms and at least one atom each of hydrogen, bromine and fluorine.
• Hydrobromofluorocarbons have ozone-depleting potential (ODP); thus, they are identified as
ozone-depleting substances (ODS).
• Ozone depleting potential is a measure of how much damage a chemical can cause to the ozone
layer compared with a similar mass of trichlorofluoromethane (CFC-11). CFC-11, with an ozone
depleting potential of 1.0, is used as the base figure for measuring ozone depletion potential. The
higher the number, the more damage a chemical can cause to the ozone layer.
Bromotrifluoromethane (halon-1301) has an ozone depleting potential of 10.0. Carbon dioxide
(CO2) is a naturally occurring greenhouse gas, but has an ozone depleting potential of 0.
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19. Hydrochlorofluorocarbons
• Hydrochlorofluorocarbons (HCFCs) are compounds made up of hydrogen , chlorine , fluorine, and
carbon atoms . HCFCs and their cousins, hydrofluorocarbons (HFCs), were created in the 1980s as
substitutes for chlorofluorocarbons (CFCs) for use in refrigeration and a wide variety of
manufacturing processes.
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20. Methyl bromide
• Bromomethane is a manufactured chemical. It also occurs naturally in small amounts in the ocean
where it is formed, probably by algae and kelp. It is a colorless, nonflammable gas with no distinct
smell. Other names for bromomethane are methyl bromide, mono-bromomethane.
• Bromomethane is used to kill a variety of pests including rats, insects, and fungi. It is also used to
make other chemicals or as a solvent to get oil out of nuts, seeds, and wool.
• Bromomethane is a one-carbon compound in which the carbon is attached by single bonds to three
bromine atoms and one hydrogen atom. It is produced naturally by marine algae. Methyl bromide
appears as colorless highly toxic volatile liquid or gas.
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23. Impacts of Ozone Layer Depletion
Harm To Human Health:-
• More skin cancers, sunburns and premature aging of the skin.
• More cataracts,blindness and other eyes disease.
Advance Impacts on Agriculture:-
• Plant growth especially in seedling, is harmed by more intense UV radiation.
• Major crop species are particularly vulnerable to increased UV, resulting in reduced growth,
photosynthesis and flowering.
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24. Effects on Plants:-
• Physiological and development processes of plants are affected by UV-B radiation, even by the amount
of UV-B is present day sunlight.
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25. Effects on animals:-
• In domastic animal, UV over exposure may cause eyes and skin cancers.
• Species of marine animals in their developmental stage, eg. young fish, shrimp larvae and crab larvae
have been threatened in recent years by the increased UV radiation under the antarctic ozone hole.
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26. Measures to prevent the ozone depletion:-
• Limit private vehicle driving.
• Use eco-friendly household cleaning products.
• Avoid using pasticides.
• Developing stringent regulations for rocket launches.
• Banning the use of dengerous nitrogen oxide.
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27. Conclusion
• there is no doubt that the problem of ozone depletion exists
and deserves extensive research and attention. With the
release of each and every CFC, our ozone layer takes one
small steps towards its destruction. The decision to ban
completely CFCs sooner than later cannot be decided by
united nations. The entire world must unite in order to expel
this problem forever.
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A mysterious spike in emissions of an ozone-destroying gas has been tracked1 to northeast China, where scientists suspect that the chemical is being produced and used in violation of international law.The chemical — trichlorofluoromethane, also known as CFC-11 — was once commonly used in spray-foam insulation for refrigerators and buildings. CFC-11 is one of the most potent chemicals responsible for creating the ozone hole in the stratosphere over the Southern Hemisphere.
