The document discusses the ozone layer, its importance in protecting life on Earth from UV radiation, and how human activities have depleted the ozone layer. It provides details on: - The location and composition of the stratospheric ozone layer. - How ozone-depleting substances (ODS) released from products like aerosols, refrigerants, and solvents travel to the stratosphere and cause ozone depletion through chemical reactions. - Evidence that the largest ozone depletions occur over the poles, with threats including increased skin cancer, cataracts, reduced crop yields, and harm to marine ecosystems and biogeochemical cycles.

2. INTRODUCTION
Planet Earth has its own natural sunscreen that shields us from the sun's damaging ultraviolet
radiation. It's called the ozone layer: a fragile band of gases beginning 15 kilometres above our planet, and
reaching up to the 40-kilometre level. Human activities have caused a substantial thinning of this protective
covering — not only over the North and South Poles, but right over our heads.
Stopping ozone layer depletion is one of the major challenges facing the world today. The stakes are
incredibly high. For the ozone layer is truly a "conserver of life," essential to the survival of all living things.
THESTRATOSPHERICOZONELAYER
The ozone layer lies in the stratosphere, in the upper level of our atmosphere. The ozone in it is
spread very sparsely. In fact, if you could squish the ozone layer to the same air pressure we have at sea
level, it would be only about as thick as the sole of your shoe.
Stratospheric ozone filters out most of the sun's potentially harmful shortwave ultraviolet (UV) radiation.
This ozone has become depleted, due to the release of such ozone-depleting substances as
chlorofluorocarbons (CFCs). When stratospheric ozone is depleted, more UV rays reach the earth. Exposure
to higher amounts of UV radiation could have serious impacts on human beings, animals and plants.
The stratospheric ozone layer sometimes gets confused with the ozone lying near the earth's surface,
known as "ground-level ozone." Although some ground-level ozone occurs naturally, most is produced by
the reaction of sunlight with chemicals found mainly in automobile exhaust and gasoline vapours. This
human-caused ozone is a key, unhealthy ingredient of smog. Ironically, we have too much ozone at ground
level and not enough in the stratosphere.

3. THE DEPLETION OF THE OZONE
In 1985, a group of scientists made an unsettling discovery: a marked decrease in
stratospheric ozone over the South Pole, in the Antarctic. The depletion appeared during the
southern hemisphere's spring (October and November) and then filled in. Soon after the Antarctic
hole was found, Canadian scientists discovered that the ozone layer above the Arctic is also thinning
significantly.
The highest latitudes — the north and south poles — experience the greatest amount of ozone loss,
during their spring. Ozone depletion is most pronounced in the Antarctic. But ozone depletion, to a
lesser degree, now occurs in the mid-latitudes. For example, the amount of stratospheric ozone over
the northern hemisphere has been dropping by 4% per decade.
What does this mean for life on earth? Even the smallest reduction in stratospheric ozone can have
a noticeable impact by increasing the amount of UV radiation that reaches the planet. Studies show,
for example, that a decrease in stratospheric ozone could cause additional deaths from skin cancer.
Even a 1% global reduction in ozone is expected to cause a significant drop in crop yields, in a world
that is already struggling to feed itself.

4. Ozone Depletion
The stratospheric ozone is being destroyed by a group of manufactured chemicals containing chlorine
and/or bromine.
It is caused by the chemicals called “ozone-depleting substances (ODS).
CHARACTERISTICSOF ODS
 STABLE
ODS are very stable, their stability allows them to float up, intact to the atmosphere. Once there,
they are broken apart by the intense ultraviolet light, releasing chlorine and bromine. Chlorine and bromine
demolish ozone at an alarming rate, by stripping an atom from the ozone molecule.
 NON-TOXIC AND ENVIRONMENTALLY SAFE
ODS are very popular because of it’s safeness in the lower atmosphere.
 HAVE A LONG LIFETIME IN THE ATMOSPHERE
ODS have a very long lifetime in our atmosphere-up to several centuries. ODS we’ve released over
the last 80 years are still making their way to the stratosphere, where they will add to the ozone destruction.

5. *1Cl atom can break down more than 100,000 ozone
molecule.

6. The MainOzone-Depleting Substances(ODS)
 Chlorofluorocarbons (CFC’s)
• The most widely used ODS, accounting for over 80% of total stratospheric ozone depletion.
• Used as coolants in refrigerators, freezers and air conditioners in buildings and cars manufactured
before 1995.
• Found in industrial solvents, dry-cleaning agents and hospital sterilants.
• Also used in foam products — such as soft-foam padding (e.g. cushions and mattresses) and rigid foam
(e.g. home insulation).
 Hydrochlorofluorocarbons (HCFC’s)
• HCFCs have become major, “transitional” substitutes for CFC’s. They are much less harmful to
stratospheric ozone than CFCs are. But HCFCs they still cause some ozone destruction and are potent
greenhouse gases.
 Halons
• Used in specialized fire extinguishers
• Has a limited application
• Can destroy up to 10 times as much as ozone as CFC’s.
• Most serious ozone-depleting group of chemicals emitted in British Columbia.

7.  Hydrofluorocarbons (HFC’s)
• Developed to replace CFC’s and HFC’s for uses such as vehicle air conditioning.
• They do not deplete ozone but are very strong greenhouse gases.
 Carbon Tetrachloride
• Used in solvents and some fire extinguishers.
 Methyl Chloroform
• Used mainly in industry — for vapour degreasing, some aerosols, cold cleaning, adhesives
and chemical processing.
 CFC’s are more powerful contributors to global climate change, though, so HCFC’s
are still the better option until even safer substitutes are discovered.

9. HealthandEnvironmentalEffectsofOzoneLayerDepletion
The Connection Between Ozone Layer Depletion and UVB Radiation
Reductions in stratospheric ozone levels will lead to higher levels of UVB reaching the Earth's surface. The sun's
output of UVB does not change; rather, less ozone means less protection, and hence more UVB reaches the Earth. Studies
have shown that in the Antarctic, the amount of UVB measured at the surface can double during the annual ozone hole.
Another study confirmed the relationship between reduced ozone and increased UVB levels in Canada during the past several
years.
Effects on Human Health
Laboratory and epidemiological studies demonstrate that UVB causes nonmelanoma skin cancer and plays a major
role in malignant melanoma development. In addition, UVB has been linked to cataracts -- a clouding of the eye’s lens. All
sunlight contains some UVB, even with normal stratospheric ozone levels. It is always important to protect your skin and eyes
from the sun. Ozone layer depletion increases the amount of UVB and the risk of health effects.
EPA uses the Atmospheric and Health Effects Framework (AHEF) model, developed in the mid 1980s, to estimate the health
benefits of stronger ozone layer protection policies under the Montreal Protocol. EPA estimates avoided skin cancer cases,
skin cancer deaths, and cataract cases in the United States.
Protecting the Ozone Layer Protects Eyesight – A Report on Cataract Incidence in the United States Using the Atmospheric
and Health Effects Framework Model (68 pp, 1.52 MB, About PDF) This 2010 peer-reviewed EPA report shows the AHEF
model’s capability to estimate avoided cataract incidence, due to improved spatial resolution and information on the
biological effects of UV radiation. A one page fact sheet summarizes the background, key findings, and future research topics
for the AHEF model on UV radiation and cataracts.
Human Health Benefits of Stratospheric Ozone Protection (PDF) (83 pp, 1.2 MB, About PDF)This 2006 peer-reviewed report
describes the analytical and empirical methodologies used by the AHEF model.
.

10. Effects on Plants
Physiological and developmental processes of plants are affected by UVB radiation, even by the amount
of UVB in present-day sunlight. Despite mechanisms to reduce or repair these effects and a limited ability to
adapt to increased levels of UVB, plant growth can be directly affected by UVB radiation.
Indirect changes caused by UVB (such as changes in plant form, how nutrients are distributed within the plant,
timing of developmental phases and secondary metabolism) may be equally, or sometimes more, important than
damaging effects of UVB. These changes can have important implications for plant competitive balance,
herbivory, plant diseases, and biogeochemical cycles.
Effects on Marine Ecosystems
Phytoplankton form the foundation of aquatic food webs. Phytoplankton productivity is limited to the
euphotic zone, the upper layer of the water column in which there is sufficient sunlight to support net
productivity. The position of the organisms in the euphotic zone is influenced by the action of wind and waves. In
addition, many phytoplankton are capable of active movements that enhance their productivity and, therefore,
their survival. Exposure to solar UVB radiation has been shown to affect both orientation mechanisms and
motility in phytoplankton, resulting in reduced survival rates for these organisms. Scientists have demonstrated a
direct reduction in phytoplankton production due to ozone depletion-related increases in UVB. One study has
indicated a 6-12% reduction in the marginal ice zone.
Solar UVB radiation has been found to cause damage to early developmental stages of fish, shrimp, crab,
amphibians and other animals. The most severe effects are decreased reproductive capacity and impaired larval
development. Even at current levels, solar UVB radiation is a limiting factor, and small increases in UVB exposure
could result in significant reduction in the size of the population of animals that eat these smaller creatures

11. Effectson BiogeochemicalCycles
Increases in solar UV radiation could affect terrestrial and aquatic biogeochemical
cycles, thus altering both sources and sinks of greenhouse and chemically-important trace
gases e.g., carbon dioxide (CO2), carbon monoxide (CO), carbonyl sulfide (COS) and possibly
other gases, including ozone. These potential changes would contribute to biosphere-
atmosphere feedbacks that attenuate or reinforce the atmospheric buildup of these gases.
Effectson Materials
Synthetic polymers, naturally occurring biopolymers, as well as some other materials
of commercial interest are adversely affected by solar UV radiation. Today's materials are
somewhat protected from UVB by special additives. Therefore, any increase in solar UVB levels
will therefore accelerate their breakdown, limiting the length of time for which they are useful
outdoors.

12. HOW TO PROTECT THE OZONE LAYER
 REDUCINGOZONE-DEPLETINGPRODUCTS
 Check your fire extinguishers to find active ingredients. If “halon” or “halogenated hydrocarbon” is
the main ingredient, find a hazardous waste center at which to recycle it, and buy a model without
this harmful ozone-depleting chemical. If you have to use your fire extinguisher, you will not be
aggressively depleting ozone while you do it.

13.  Don’t buy aerosol products with chlorofluorocarbons (CFC). Although CFCs have been banned or
reduced in many applications, the only way to be sure is to check the label on all your hairsprays,
deodorants and household chemicals. Opt for pump spray products over pressurized cans, to further
reduce your chance of buying CFCs.

14.  Repair your refrigerator, freezer and air conditioning units immediately upon any sign of
problems. These devices use an ozone-depleting chemical to function, so leaks release the
chemical into the atmosphere. If these devices break, find a safe place to recycle the item so that it
will not leak Freon into the atmosphere.
 Purchase new refrigerators, freezers or air conditioners that don’t contain Freon or other
chlorofluorocarbons. Most manufacturers produce models with fluorine, rather than chlorine that
do not deplete the ozone layer.

15.  Buy lumber, wood products and plywood that were not treated with methyl bromide. This pesticide
is used commonly to fumigate; however, its industrial use is still actively depleting the ozone
layer.Researching and choosing construction products that don’t employ bromomethane could be
just as important as stopping the use of CFCs at home, since elemental bromine has been found to
be more toxic to the ozone layer than chlorine.

16.  Don’t buy office products like liquid correction fluid or compressed air that contain methyl
chloroform. This is also known as “1,1,1-trichloroethane.” It is popular as a solvent, but is also depleting the
ozone layer.

17.  Advocating For Ozone Protection
 Look into your food sources. If your state and country still allows the use of bromomethane, write a
letter or call your local representatives to demand that this harmful pesticide and ozone-depleting
chemical be removed.

18.  Ask your doctor about prescribing medical devices that don’t emit CFCs. This is especially important with
asthma, a common ailment. Inhalers still use CFCs to dispense life-saving medication.

19.  Sign petitions or write letters to companies that make products with CFCs to ensure they are
labeling their products correctly. If your hairspray, aerosol cans or fire extinguishers don’t say halon,
CFCs or methyl chloroform.

20.  Talk to friends, especially those in car, farming and manufacturing industries, about reducing their use of
these chemicals. The hole in the ozone can only repair itself if these chemicals are eradicated and the ozone
layer has time to reform.

21. The End…
Thank You! 
Prepared by: Group5