International Journal of IT, Engineering and Applied Sciences Research (IJIEASR)
Volume 4, No. 8, August 2015
ISSN: 2319-4413
Ozone Depletion: Its Causes, Effects & Protective Measures
Ramanjeet Kaur, Assistant Professor, Physics Department, R. S. D. College, Firozpur city, Punjab, India
ABSTRACT
The ozone layer forms a thick layer in stratosphere,
encircling the earth that protects our planet from the
harmful radiations. But this protective layer is being
depleted. The natural phenomena such as Sun-spots &
stratospheric winds and mainly man-made causes like
excessive release of chlorine and bromine are responsible
for it. Many efforts like the Clean Air Act, Montreal
Protocol and prohibition of ozone depleting substances
are done for the protection of ozone layer. The harmful
effects of ozone depletion on human Health, marine
ecosystems, bio-geo-chemical Cycles and on materials are
discussed.
Keywords
Ultraviolet light, ozone depletion, stratosphere, halons,
chloroflourocarbons, greenhouse effect
1. INTRODUCTION
Ozone layer is a deep layer in earth’s atmosphere that
contains ozone which is a naturally occurring molecule
containing three oxygen atoms. These ozone molecules
form a gaseous layer in the Earth’s upper atmosphere 6.2
to 31 miles (10 to 50 kilometers) above Earth, in the
region called the stratosphere. These molecules are
constantly being formed and broken down in the high
atmosphere. The average concentration of ozone in the
atmosphere is around 0.6 parts per million. The thickness
of the ozone layer differs as per season and geography.
The highest concentrations of ozone occur at altitudes
from 26 to 28 km (16 to 17 miles) in the tropics and from
12 to 20 km (7 to 12 miles) towards the poles. The ozone
layer was discovered in 1913 by the French physicists
Charles Fabry and Henri Buisson. An essential property of
ozone molecule is its ability to block solar radiations of
wavelengths less than 290 nanometers from reaching
Earth’s surface. In this process almost 97-99% of the
harmful ultraviolet radiations that sun emit and which can
produce long term devastating effects on human beings as
well as plants and animals [1].
In the past 60 years or so human activity has contributed to
the deterioration of the ozone layer. The ozone hole is not
technically a “hole” where no ozone is present, but is
actually a region of exceptionally depleted ozone in the
stratosphere over the Antarctic that happens at the
beginning of Southern Hemisphere spring (August–
October). The ozone hole is defined geographically as the
area wherein the total ozone amount is less than 220
Dobson Units. From the historical record we know that
total column ozone values of less than 220 Dobson Units
were not observed prior to 1979. 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 [2].
2. CAUSES OF DEPLETION OF OZONE
LAYER
Ozone is constantly produced and destroyed in a natural
cycle. Each spring in the stratosphere over Antarctica
(Spring in the southern hemisphere is from September
through November), atmospheric ozone is rapidly
destroyed by chemical processes. As winter arrives, a
vortex of winds develops around the pole and isolates the
polar stratosphere. When temperatures drop below -78°C
(-109°F), thin clouds are formed from ice, nitric acid, and
sulphuric acid mixtures. Chemical reactions on the
surfaces of ice crystals in the clouds release active forms
of CFCs. Ozone depletion begins, and the ozone “hole”
appears. Over the course of two to three months,
approximately 50% of the total column amount of ozone
in the atmosphere disappears. At some levels, the losses
approach 90%. In spring, temperatures begin to rise, the
ice evaporates, and the ozone layer starts to recover. In
this way the overall amount of ozone remains essentially
stable. But this was the situation until the past several
decades [3]. Now human activities have resulted in
considerable reduction in the ozone layer of the
atmosphere. Ozone depletion occurs when destruction of
the stratospheric ozone is more than the production of the
molecule. The scientists have observed reduction in
stratospheric ozone since early 1970s. It is found to be
more prominent in Polar Regions.
There are two regions in which the ozone layer has
depleted.
In the mid-latitude, for example, over Australia, ozone
layer is thinned. It is estimated that about 5-9% thickness
of the ozone layer has decreased, increasing the risk of
humans to over-exposure to UV radiation owing to
outdoor lifestyle.
In atmospheric regions over Antarctica, ozone layer is
significantly thinned, especially in spring season. This has
led to the formation of what is called ‘ozone hole’. One of
i-Explore International Research Journal Consortium
www.irjcjournals.org
12
International Journal of IT, Engineering and Applied Sciences Research (IJIEASR)
Volume 4, No. 8, August 2015
the largest such hole appears annually over Antarctica
between September and November [4].
A. Natural Causes of Depletion of Ozone Layer
Ozone layer has been found to be affected by certain
natural phenomena such as Sun-spots and stratospheric
winds. But this has been found to cause not more than 12% depletion of the ozone layer and the effects are also
thought to be only temporary. It is also believed that the
major volcanic eruptions (mainly El Chichon in 1983 and
and Mt. Pinatubo in 1991) has also contributed towards
ozone depletion.
•
B. Man Made Causes of Depletion of Ozone Layer
The main cause for the depletion of ozone is determined as
excessive release of chlorine and bromine from man-made
compounds such as chlorofluorocarbons (CFCs). CFCs
(Methyl
(chlorofluorocarbons),
halons,
CH3CCl3
chloroform), CCl4 (Carbon tetrachloride), HCFCs (hydrochlorofluorocarbons), hydro-bromo-fluoro-carbons and
methyl bromide are found to have direct impact on the
depletion of the ozone layer. These are categorized as
ozone-depleting substances (ODS).
The problem with the Ozone-Depleting Substances (ODS)
is that they are not washed back in the form of rain on the
earth and in-fact remains in the atmosphere for quite a
long time. With so much stability, they are transported into
the stratosphere. The emission of ODS account for roughly
90% of total depletion of ozone layer in stratosphere.
These gases are carried to the stratosphere layer of
atmosphere where ultraviolet radiations from the sun break
them to release chlorine (from CFCs) and bromine (from
methyl bromide and halons). The chlorine and bromine
free radicals react with ozone molecule and destroy their
molecular structure, thus depleting the ozone layer. One
chlorine atom can break more than 1,00,000 molecules of
ozone. Bromine atom is found to be 40 times more
destructive than chlorine molecules [5]. The main ozone
depleting substances and their release to atmosphere has
been discussed:
C. Main Ozone Depleting Substances
• Chlorofluorocarbons: These account for more than
80% of ozone depletion. These are used in freezers,
air cooling component, dry-cleaning agents,
hospital sterilants. CFC-11, CFC-12 and HCFC22 are used as refrigerant in domestic airconditioners and refrigerators as well as retail store
refrigeration systems, chillers and air-conditioners.
CFC-11 and CFC-12 are used as propellants for
aerosol sprays such as hair mousses and household
cleaning products. CFC-11 and CFC-12 are also
used as blowing agents in the manufacture of foams
for home furnishing, insulation and packaging.
Some plastics may be shaped using CFCs, e.g. egg
cartons, cups and cartons used in fast food
•
•
ISSN: 2319-4413
operations. Rigid or semi-rigid foams are also used
as thermal or sound insulation in refrigeration
equipment, buildings and automobiles. CFC-113 is
a solvent for cleaning electronic circuit boards and
computer components.
Halons are used as fire extinguishing agents, in
cases where materials and equipment would be
destroyed by water or other fire extinguisher
chemicals. Bromochlorodifluoromethane (BCF) is
commonly used in portable fire extinguishers.
Bromotrifluoromethane (BTM) is used in fixed firefighting installations. These cause greater damage
to the ozone layer than do CFCs from automobile
air conditioners.
Methyl Chloroform is used for vapor degreasing,
some aerosols, cold cleaning, adhesives and
chemical processing.
Hydrochlorofluorocarbons have become major,
“transitional” substitutes for CFCs. They are much
less harmful to stratospheric ozone than CFCs are.
But HCFCs they still cause some ozone destruction
and are potent greenhouse gases [6].
Methyl bromide, hydrobromofluorocarbons (HBFCs) and
bromochloromethane (BCM) are other ozone depleting
substances.
.
3. HEALTH AND ENVIRONMENTAL
EFFECTS OF OZONE DEPELTION
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. A worldwide thinning of the ozone
layer would have very serious implications for all life on
Earth. Effects range from an increased incidence of skin
cancer and other diseases in humans, to crop damage and
disruptions to fragile ecosystems. The medical,
environmental and economic costs become tremendous.
Few effects are discussed below:
A. Effects on Human Health
Increased UV levels at the earth's surface are damaging to
human health. 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. The reason UV-B is so damaging is that it
can be readily absorbed by DNA the molecule within the
cells of our body that contains our genetic code. When
DNA is disrupted the instructions cannot be read properly.
As the amount of UV-B entering the cell increases then so
i-Explore International Research Journal Consortium
www.irjcjournals.org
13
International Journal of IT, Engineering and Applied Sciences Research (IJIEASR)
Volume 4, No. 8, August 2015
does the risk of genetic damage. If it gets too bad it can
result in disease or even death. The most common human
impact of UV-B radiation is skin cancer, which accounts
for more than 1,000 deaths each year in the UK. Other
negative effects include eye cataracts and immune
deficiency disorders. Increased penetration of UV results
in additional production of ground level ozone, which
causes respiratory illnesses.
B. 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, distribution of nutrients are 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.
C. Environmental Effects
UV affects terrestrial and aquatic ecosystems, altering
growth, food chains and biochemical cycles. In particular,
aquatic life occurring just below the surface of the water,
which forms the basis of the food chain, is adversely
affected by high levels of UV radiation. Phytoplankton
productivity is limited to the upper layer of the water
column in which there is sufficient sunlight to support net
productivity. The position of the organisms in this 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 depletionrelated increases in UVB.
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. UV
rays also have adverse effects on plant growth, thus
reducing agricultural productivity. Furthermore, depletion
of stratospheric ozone also alters the temperature
distribution in the atmosphere, resulting in a variety of
environmental and climatic impacts.
ISSN: 2319-4413
D. Effects on Biogeochemical Cycles
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 sulphide (COS) and possibly other gases,
including ozone. These potential changes would contribute
to biosphere-atmosphere feedbacks that attenuate or
reinforce the atmospheric build up of these gases.
E. Economic Effects
Increased health costs are the most important direct
economic impact of increased UV radiation. The medical
expenses for millions of additional cases of skin cancers
and eye cataracts pose a challenge to health care systems,
particularly in less developed countries. 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 le els will accelerate
their breakdown, limiting the length of time for which they
are useful outdoors. Increased UV radiation also reduces
the lifetime and tensile properties of certain plastics and
fiber.
Indirect economic impacts include a range of additional
costs, for instance for combatting climate change or as a
result of reduced fish stocks [7-8].
F. The Ozone Depletion and Global Warming
Global warming and ozone depletion are two separate
environmental problems but there are links between the
two. As well as damaging the ozone layer, CFCs are also
greenhouse gases and contribute to global warming. Since
the introduction of the Montreal Protocol there have been
increased concentrations in the atmosphere of their
replacement – HFCs and HCFCs. Unfortunately, although
HFCs and HCFCs cause less damage to the ozone layer,
they are greenhouse gases. There is also another
connection between ozone depletion and global warming.
Although the greenhouse effect warms the Earth’s surface
it also allows the higher atmosphere, where ozone is
present, to cool. This means that more stratospheric clouds
may form, increasing the damage to the ozone layer and
delaying its ultimate recovery.
4.
PROTECTION
OF
STRATOSPHERIC OZONE LAYER
THE
In the mid-1970s, scientists became concerned that
chlorofluorocarbons (CFCs) could destroy stratospheric
ozone. In the 1980s, scientists began accumulating
evidence that the ozone layer was being depleted. In 1978,
the U.S. government banned CFCs as propellants in most
aerosol uses.
i-Explore International Research Journal Consortium
www.irjcjournals.org
14
International Journal of IT, Engineering and Applied Sciences Research (IJIEASR)
Volume 4, No. 8, August 2015
In 1987 a comprehensive agreement was drawn up to limit
the production and use of CFCs. The Montreal Protocol
has been hailed as one of the most successful international
agreements ever implemented. In September 1987, an
international treaty aimed at saving the Earth's ozone
layer, known as the Montreal Protocol on Substances that
Deplete the Ozone Layer, was signed in Montreal, Canada.
Over 190 countries, including the major industrialized
nations such as the United States, have signed the
Montreal Protocol, which calls for elimination of
chemicals that destroy stratospheric ozone. Countries that
signed the Protocol are committed to limiting the
production and use of those chemicals. Originally aimed at
halving the use of CFCs by 1999, reviews of the Protocol
went further, imposing stringent controls. As a result,
developed countries agreed to phase out the production of
CFCs and halons by the year 2000. In the UK,
consumption of CFCs had ceased by 1995, except for
essential uses including metered dose inhalers for medical
conditions such as asthma. By the end of 2009, all the UN
member states had signed the basic Protocol. CFC
production anywhere should have stopped by 1st January
2010.
The 1990 Clean Air Act required EPA to set up a
program for phasing out production and use of ozonedestroying chemicals. In 1996, U.S. production ended for
many of the chemicals capable of doing the most serious
harm such as CFCs, halons, and methyl chloroform. The
Clean Air Act includes other steps to protect the ozone
layer. The Act encourages the development of "ozonefriendly" substitutes for ozone-destroying chemicals.
Many products and processes have been reformulated to
be more "ozone-friendly." For instance, refrigerators no
longer use CFCs [9].
There has been considerable progress in finding nonozone-depleting substitutes for ODS in the last few
years. Substitutes for air-conditioning and refrigeration
applications are now available, such as that HCFC-22 can
be replaced by HFC-410A, CFC-12 can be replaced by
HFC-134a. There are also emerging markets for "drop-in"
replacement for HCFCs and halons. Alternative products
or processes can be used in some cases like alternative
insulating materials, substitute food containers such as
hydrocarbon blown polystyrene, plastic film wrap and
bags; alternative packaging materials such as plastic film
bubble wraps; and air-conditioning and refrigeration plants
operating on non-HCFC refrigerants. HCFCs solvents can
be substituted in some applications. For instance,
petroleum solvents can be selected as a replacement for
CFC-113 or 1,1,1-trichloroethane in cleaning applications.
Aqueous cleaning, or even no-clean technology, are also
alternative processes that can be used by the electronics
industry. Many household and personal aerosol products,
e.g. paint sprays and insecticides, now use hydrocarbons
ISSN: 2319-4413
(e.g. propane and butane) as propellants instead of HCFCs
or CFCs.
Service stations must have special equipment that prevents
release of refrigerant chemicals to the air when they are
recharging car air conditioning systems.
Many international efforts are done to protect ozone
layer. The Import Banning Amendment regulation
prohibits the import of controlled products containing
HCFCs, CFCs and halons, etc. like an air-conditioner or
heat pump designed to cool the driver's or passengers'
compartment of a motor vehicle, refrigeration equipment
or air-conditioning or heat pump equipment (whether for
domestic or commercial use), insulation panel, insulation
board or insulation pipe cover; a pre-polymer, portable fire
extinguishers containing CFCs, halons, HCFCs or BCM.
Controlled Refrigerants Regulation prohibits any
intended release of controlled refrigerants from motor
vehicle air-conditioners or refrigeration equipment
containing more than 50 kg of refrigerant charge into the
atmosphere, and to conserve the controlled refrigerants
through the use of approved recycling and recovery
equipment [10].
Despite existing regulation of ODS, there continues to be
severe ozone depletion. This is because once released,
ODS stay in the atmosphere for many years and continue
to cause damage. However, since smaller and smaller
amounts of ODS are being released, the first signs of
recovery of the ozone layer are visible. Nevertheless,
because of the long lifetime of ODS, and unless additional
measures are taken, the ozone layer is unlikely to recover
fully before the second half of the century.
5. CONCLUSION
Ozone layer is protective cover of the earth. Its depletion
leads to harmful effects on every aspect of human life.
Efforts are being done to phase out ozone destroying
chemicals but sometimes it isn't easy. For instance,
substitutes have not been found for CFCs used in certain
medical applications. The limit on the production of
methyl bromide, a pesticide, was extended because no
effective alternative was found. Despite all this ozonedestroying chemicals are being tried to phase out and with
continued work, over time the protective ozone layer will
be repaired which is essential for saving life on earth.
REFERENCES
i-Explore International Research Journal Consortium
[1] http://www.conserve-energy-future.com/wpcontent/uploads/2013/05/Ozone_hole.jpghttp://ww
w.conserve-energy-future.com/wp-content/uploads
/2013/05/Ozone_hole.jpg
www.irjcjournals.org
15
International Journal of IT, Engineering and Applied Sciences Research (IJIEASR)
Volume 4, No. 8, August 2015
ISSN: 2319-4413
[2] http://ozonewatch.gsfc.nasa.gov/facts/hole.html
[3] http://www.epa.gov/ozone/science/process.html
[4] http://www.conserve-energy-future.com/wpcontent/uploads/2013/05/Ozone_layer_depletion.jp
ghttp://www.conserve-energy-future.com/wp-co
ntent/uploads/2013/05/Ozone_layer_depletion.jpg
[5] http://www.conserve-energy-future.com/ozonelayer-and-causes-of-ozone-depletion.php
[6] http://www.bcairquality.ca/101/ozone-depletioncauses.html
[7] http://www.epa.gov/ozone/science/effects/
[8] http://ec.europa.eu/clima/policies/ozone/faq_en.htm
[9] http://www.epa.gov/airquality/peg_caa/stratozone.h
tml
[10] http://www.epd.gov.hk/epd/english/environmentin
hk/air/ozone_layer_protection/wn6_info_olp_ue_c.
html
i-Explore International Research Journal Consortium
www.irjcjournals.org
16