Ozone Layer Depletion Essay

ISSUES AND CONCERNS ABOUT THE OZONE LAYER DEPLETION INTRODUCTION The ozone layer protects the Earth from the ultraviolet rays sent down by the sun. If the ozone layer is depleted by human action, the effects on the planet could be catastrophic. In recent years, the ozone layer has been the subject of much discussion. And rightly so, because the ozone layer protects both plant and animal life on the planet. The atmosphere is divided into five layers:  the troposphere, the stratosphere, the mesosphere, the thermosphere, and the exosphere.

The troposphere is the layer closest to earth and is where all weather happenings occur. The stratosphere is located directly above the troposphere, about 10-50 kilometers above the planet, and houses the ozone layer at an altitude of 20-30 kilometers. The mesosphere is located approximately 50-80 kilometers above the earth, while the thermosphere rests at an altitude of approximately 100-200 kilometers above the earth’s surface. Finally, the boundary of the outermost layer, the exosphere, extends roughly to 960-1000 kilometers above the earth.

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Figure 1:  Earth’s atmosphere is divided into layers, which have various characteristics. The ozone levels have decreased to a normal level. Normal meaning the levels have dropped from the levels reported in 1980. The ozone layer is an important and fragile part of earth. If we did not have an ozone layer between 10km and 50km, high ultraviolet radiation would pour through. This would create harmful living conditions for all life forms. The fact that the ozone layer was being depleted was discovered in the mid-1980s. The main cause of this is the release of CFCs, chlorofluorocarbons.

Antarctica was an early victim of ozone destruction. A massive hole in the ozone layer right above Antarctica now threatens not only that continent, but many others that could be the victims of Antarctica’s melting icecaps. In the future, the ozone problem will have to be solved so that the protective layer can be conserved. The ozone layer:  What is it? The ozone layer is a portion of earth’s atmosphere that contains high levels of ozone. The ozone found in our atmosphere is formed by an interaction between oxygen molecules (composed of two oxygen atoms) and ultraviolet ight. When ultraviolet light hits these oxygen molecules, the reaction causes the molecules to break apart into single atoms of oxygen. These single atoms of oxygen are very reactive, and a single atom combines with a molecule of oxygen to form ozone, which is composed of three atoms of oxygen. The ozone layer protects the Earth from the ultraviolet rays sent down by the sun. If the ozone layer is depleted by human action, the effects on the planet could be catastrophic. The ozone layer is essential for human life.

It is able to absorb much harmful ultraviolet radiation, preventing penetration to the earth’s surface. Ultraviolet radiation (UV) is defined as radiation with wavelengths between 290-320 nanometers, which are harmful to life because this radiation can enter cells and destroy the deoxyribonucleic acid (DNA) of many life forms on planet earth. In a sense, the ozone layer can be thought of as a ‘UV filter’ or our planet’s ‘built in sunscreen’ (Geocities. com, 1998). Without the ozone layer, UV radiation would not be filtered as it reached the surface of the earth.

If this happened, ‘cancer would break out and all of the living civilizations, and all species on earth would be in jeopardy’ (Geocities. com, 1998). Thus, the ozone layer essentially allows life, as we know it, to exist. Figure 2:  Ozone thickness over Labrador, Canada measured in Dobson Units CAUSES OF OZONE LAYER DEPLETION Ozone depletion:  Who is responsible? It is important to recognize the sources of ozone depletion before one can fully understand the problem. There are three main contributors to the ozone problem: human activity, natural sources, and volcanic eruptions.

Figure 3:  Humans cause more damage to the ozone layer than any other source. Ozone depletion occurs when the natural balance between the production and destruction of stratospheric ozone is tipped in favour of destruction. Although natural phenomena can cause temporary ozone loss, chlorine and bromine released from man-made compounds such as CFCs are now accepted as the main cause of this depletion. The production and emission of CFCs, is by far the leading cause. Human activity is by far the most prevalent and destructive source of ozone depletion, while threatening volcanic eruptions re less common. Human activity, such as the release of various compounds containing chlorine or bromine, accounts for approximately 75 to 85 percent of ozone damage. Perhaps the most evident and destructive molecule of this description is chloroflourocarbon (CFC). CFCs were first used to clean electronic circuit boards, and as time progressed, were used in aerosols and coolants, such as refrigerators and air conditioners. When CFCs from these products are released into the atmosphere, the destruction begins. As CFCs are emitted, the molecules float toward the ozone rich stratosphere.

Then, when UV radiation contacts the CFC molecule, this causes one chlorine atom to liberate. This free chlorine then reacts with an ozone (O3) molecule to form chlorine monoxide (ClO) and a single oxygen molecule (O2). This threatening chlorine atom then continues the cycle and results in further destruction of the ozone layer. Measures have been taken to reduce the amount of CFC emission, but since CFCs have a life span of 20-100 years, previously emitted CFCs will do damage for years to come. Figure 4:  A pictorial explanation of how the interaction of CFCs and UV radiation damage the ozone layer.

Many countries have called for the end of CFC production because only a few produce the chemical. However, those industries that do use CFCs do not want to discontinue usage of this highly valuable industrial chemical. CFCs are used in industry in a variety of ways and have been amazingly useful in many products. CFCs came to be used in refrigerators, home insulation, plastic foam, and throwaway food containers. Only later did people realize the disaster CFCs caused in the stratosphere. There, the chlorine atom is removed from the CFC and attracts one of the three oxygen atoms in the ozone molecule.

Only in 1984, when the ozone layer hole was discovered over Antarctica, was the proof truly conclusive. At that point, it was hard to question the destructive capabilities of CFCs. Chlorofluorocarbons are not “washed” back to Earth by rain or destroyed in reactions with other chemicals. They simply do not break down in the lower atmosphere and they can remain in the atmosphere from 20 to 120 years or more. As a consequence of their relative stability, CFCs are instead transported into the stratosphere where they are eventually broken down by ultraviolet (UV) rays from the Sun, releasing free chlorine.

The chlorine becomes actively involved in the process of destruction of ozone. Emissions of CFCs have accounted for roughly 80% of total stratospheric ozone depletion. Thankfully, the developed world has phased out the use of CFCs in response to international agreements to protect the ozone layer. However, because CFCs remain in the atmosphere so long, the ozone layer will not fully repair itself until at least the middle of the 21st century. Naturally occurring chlorine has the same effect on the ozone layer, but has a shorter life span in the atmosphere. Even if CFCs were banned, problems would remain.

There would still be no way to remove the CFCs that are now present in the environment. Clearly though, something must be done to limit this international problem in the future. Natural sources also contribute to the depletion of the ozone layer, but not nearly as much as human activity. Natural sources can be blamed for approximately 15 to 20 percent of ozone damage. A common natural source of ozone damage is naturally occurring chlorine. Naturally occurring chlorine, like the chlorine released from the reaction between a CFC molecule and UV radiation, also has detrimental effects and poses danger to the earth.

Finally, volcanic eruptions are a small contributor to ozone damage, accounting for one to five percent. During large volcanic eruptions, chlorine, as a component of hydrochloric acid (HCl), is released directly into the stratosphere, along with sulfur dioxide. In this case, sulfur dioxide is more harmful than chlorine because it is converted into sulfuric acid aerosols. These aerosols accelerate damaging chemical reactions, which cause chlorine to destroy ozone. HEALTH AND ENVIRONMENTAL EFFECTS OF OZONE LAYER DEPLETION Even minor problems of ozone depletion can have major effects.

Every time even a small amount of the ozone layer is lost, more ultraviolet light from the sun can reach the Earth. Every time 1% of the ozone layer is depleted, 2% more UV-B is able to reach the surface of the planet. UV-B increase is one of the most harmful consequences of ozone depletion because it can cause skin cancer. The increased cancer levels caused by exposure to this ultraviolet light could be enormous. The EPA estimates that 60 million Americans born by the year 2075 will get skin cancer because of ozone depletion. About one million of these people will die.

In addition to cancer, some research shows that a decreased ozone layer will increase rates of malaria and other infectious diseases. According to the EPA, 17 million more cases of cataracts can also be expected. The environment will also be negatively affected by ozone depletion. The life cycles of plants will change, disrupting the food chain. Effects on animals will also be severe, and are very difficult to foresee. Oceans will be hit hard as well. The most basic microscopic organisms such as plankton may not be able to survive.

If that happened, it would mean that all of the other animals that are above plankton in the food chain would also die out. Other ecosystems such as forests and deserts will also be harmed. The planet’s climate could also be affected by depletion of the ozone layer. Wind patterns could change, resulting in climatic changes throughout the world. 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.

All sunlight contains some UVB, even with normal ozone levels. It is always important to limit exposure to the sun. However, ozone depletion will increase the amount of UVB and the risk of health effects. According to the Environmental Protection Agency, they predict that for every one percent drop in global ozone, there would be a one to three percent increase in skin cancer. Ultraviolet light can kill many forms of life, even bacteria. This is why ultraviolet light is used to sterilize surgical equipment. Ultraviolet also kills beneficial forms of life and can affect the life cycle of many organisms.

Ozone depletion and skin cancer:  What’s the connection? Exposure to UV radiation increases the risk of skin cancer and causes damage to the DNA in the skin cells. DNA is extremely sensitive to UV radiation, especially UV-B radiation. UV radiation is located in the optical radiation portion of the electromagnetic spectrum, while UV-B radiation is a subdivision of the ultraviolet spectrum and consists of a wavelength of 280 to 315 nanometers. When UV radiation hits the skin, it can cause the cell to ‘lock up’ and scramble or delete DNA information.

This action causes confusion in the DNA, and the body loses control of the growth and division of the cell. If the conditions are right, the cell may become cancerous. It is important to note that not all affected cells turn into skin cancer, for many can repair themselves. However, continual exposure to UV radiation increases the risk of skin cancer due to cumulative damage of the DNA. Skin cancer can be divided into two categories: melanoma and non-melanoma. The melanoma form of skin cancer is the more dangerous of the two.

This type of cancer has the ability to spread quickly throughout the body and invade other cells. On the other hand, non-melanoma skin cancer is not to be taken lightly either, but is a less serious form of the disease. Non-melanoma skin cancers are not usually life threatening, and removal is relatively routine. However, treatment does include radiation therapy or surgery. The concern of many is that sunburn may lead to increased risk of acquiring skin cancer. Some forms of cancer are associated with sunburn, while other forms are not. Melanoma skin cancer is a form that sunburns may play a leading role in.

Jan van der Leun, a Dutch scientist, explains that, ‘light hitting the outer layer of the skin, the epidermis, triggers the production of some substances which diffuse into the dermis below. The dermis is filled with blood vessels, and the chemical substances cause them to dilate, making the skin red and warm to the touch’ (Nilsson, 83). The bottom line is that UV ray exposure increases the risk of skin cancer. However, controversy lies around the question of whether or not the depletion of the ozone layer will lead to more sunburns, and in turn, more skin cancer.

Some scientists suggest that the skin will gradually adapt to higher UV-B levels as the ozone gradually depletes (Nilsson, 83). The opponent to this theory would state that the thinning of the ozone layer would lead to more human UV-B exposure. This increased UV-B exposure would, in turn, increase the damage to the DNA making it difficult for the cell to correct the damage before it divides. This damage accumulates over time and increases the chances that a cell will turn cancerous. In addition, since UV-B radiation damages the immune system, it is much more likely that a cell will turn cancerous. In animal studies, immunosuppressive effects caused by UV-B have indeed been shown to play an important role in the outcome of both melanoma and non-melanoma skin cancers’ (Nilsson, 105). Furthermore, Nilsson (81) states that ‘for the non-melanoma skin cancers, the evidence is compelling and there are estimates that each percentage decrease in the stratospheric ozone will lead to a two percent increase in the incidence of these cancers. ’  Thus, if the ozone depletes by ten percent over a certain time period, 250,000 more people would be affected by these cancers each year (Nilsson, 81).

Due to controversy in the scientific community, it is difficult to clearly state whether or not ozone depletion will lead to an increased risk of skin cancers, but scientists agree on the fact that UV-B radiation plays a large role in the formation of cancer. Thus, it may very well be that as the ‘UV filter’ we call the ozone layer thins, the increased amount of UV-B radiation posed on human skin may contribute to an increased amount of skin cancer. Yet, one can only weigh all the evidence and speculate, for science has yet to provide a ‘cut and dry’ answer for society to base its judgments on. Ozone depletion and immuno-suppression

Ozone depletion is also suggested to cause immuno-suppression. This theory was first explored in the 1960s when guinea-pigs, who were exposed to an allergen, showed a lowered immune system response after they had been irradiated with UV (Nilsson, 101). In addition, another study showed that UV radiation had the same effect on animals as X-ray treatment and chemical immuno-suppression. Logically, all three factors suppressed the immune system. Scientists Edward de Fabo and Frances Noonan conducted a study to investigate exactly which portion of the UV spectrum has the power to suppress the immune system.

In this experiment, de Fabo and Noonan employed filters that were able to separate UV radiation wavelength by wavelength. They subjected mice to UV rays and measured the effects at precise intervals on the UV range. ‘When de Fabo and Noonan started to match the parts of the spectrum that gave the most immuno-suppression with the absorption spectra of different compounds in the skin, they found an almost perfect match ‘ UCA, the compound previously thought of as sunscreen (Nilsson, 102).   Nilsson (107) describes urocanic acid (UCA) as antenna-like because it attracts UV rays. When UV radiation hits the skin, it causes UCA within the skin to change molecular structure from trans-UCA to cis-UCA. This transformation interacts with a number of cells in the skin and sends a signal to the immune system, causing it to hinder its reaction. Although there is clear evidence supporting the fact that cumulative UV-B exposure leads to immuno-suppression, it is difficult to determine whether people will get ill because of ozone depletion. Logically, thinning of the ozone ayer leads to increased exposure to UV-B radiation, which in turn leads to increased chances of immuno-suppression, but scientists cannot form an answer based solely on that information. Despite the fact that there is not a clear answer, in viewing and studying the data, science suggests that there is the possibility of increased illness as a result of the thinning ozone layer. Other Illnesses Like immuno-suppression and skin cancer, science is not able to provide society with a confident answer to the question: Will the depletion of the ozone layer cause an increased number of cataract cases?

Cataracts are a condition that begin with blurry vision and in some cases, develop into blindness. It has been proven that UV light can damage the DNA, membranes, and proteins in the eye, and in animal studies, this damage has resulted in scattered light and the formation of opaque areas in the eye. It was estimated by the Environmental Effects Panel of the United Nations Environment Programme that for each percent decrease in ozone, the number of people developing blindness would increase by approximately 100,000 to 150,000 people (Nilsson, 113).

However, this estimation was contradicted by a team of Dutch scientists, who stated, ‘it is not scientifically justifiable to quantify the effects of UV radiation on the eye, if such effects are present under normal circumstances’ (Nilsson, 113). The UNEP then published an updated statement and included information that poor diet and diseases, such as diabetes, also contribute to cataract development. Thus, it must be recognized that cataracts can result from poor nutrition, poor hygiene, and diabetes, and not solely from increased UV radiation.

Research has been conducted to investigate a link between cataracts and UV radiation. Some epidemiological studies have shown that UV-B radiation and formation of cataracts do have a positive relationship. For example, a study conducted with Chesapeake Bay fishermen asked these fishermen to disclose whether or not they wore sunglasses while working and during outdoor recreational activities. Then, radiation measurements were taken throughout the area to probe for a correlation. The results of this study showed a ‘weak positive dose-response relationship with UV-B exposure’ (Nilsson, 117).

Thus, in this study, one would argue that increased UV radiation would lead to increased rates of cataracts. Many other studies have been conducted to examine this phenomenon, and none have shown a strongly correlated causal relationship between UV-B and cataracts, but many suggest the possibility of a relationship. In summary, there is again no ‘cut and dry’ answer explaining what will happen to the number of cases of cataracts as the ozone layer depletes, but when one examines the effects of UV-B radiation on the eyes, it is suggested that ozone depletion is likely to increase one? s risk of developing cataracts.

A short-term health problem that will increase as the level of ozone decreases is ‘snowblindness’ or ‘welder;s arc flash. ’  This phenomenon is a result of sunburn of the conjunctiva and cornea and is ‘characterized by blurred vision, severe pain, photophobia, profuse tearing, and eyelid spasms’ (Ozone. org, 1998). The condition occurs after exposure to UV-B radiation and does not result in permanent damage. The symptoms usually vanish after a few days. It is obvious to recognize the controversy surrounding theories which state that depletion of the ozone layer causes health problems.

While one resource may provide the reader with one answer, the next source may provide the opposite theory. It is evident that UV radiation causes various health problems, but what is not so clear is to what degree a depleting ozone layer will magnify the occurrence of these problems. 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. 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 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. Effects on 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. SOLUTIONS FOR OZONE LAYER DEPLETION The discovery of the ozone depletion problem came as a great surprise. Now, action must be taken to ensure that the ozone layer is not destroyed. Because CFCs are so widespread and used in such a great variety of products, limiting their use is hard.

Also, since many products already contain components that use CFCs, it would be difficult if not impossible to eliminate those CFCs already in existence. The CFC problem may be hard to solve because there are already great quantities of CFCs in the environment. CFCs would remain in the stratosphere for another 100 years even if none were ever produced again. Despite the difficulties, international action has been taken to limit CFCs. In the Montreal Protocol, 30 nations worldwide agreed to reduce usage of CFCs and encouraged other countries to do so as well.

However, many environmentalists felt the treaty did “too little, too late”, as the Natural Resources Defense Council put it. The treaty asked for CFC makers to only eliminate half of their CFC production, making some people feel it was inadequate. Many other countries have signed treaties and written laws restricting the use of CFCs. Companies are finding substitutes for CFCs, and people in general are becoming more aware of the dangers of ozone depletion. A high ozone depletion in 1987, led to the Montreal Protocol.

In an effort to resolve ozone depletion, the protocol banned all harmful CFC’s and any other chemicals that affected the ozone. Ever since then the ozone depletion is slowly recovering. The ozone layer will take years to recover, even after we remove all ozone destroying chemicals. An international panel believes the global levels of ozone depletion should improve by the year 2020, or even longer if Russia and other countries don’t meet their obligations. SUMMARY , CONCLUSIONS AND RECOMMENDATIONS The ozone layer is essential for protecting society from harmful UV radiation by acting as a filter.

However, this protective layer has been thinning due to three main sources: human activity, natural sources, and volcanoes. Human activity is responsible for the most damage to the ozone layer, thus, society should recognize that much can be done to prevent ozone layer damage. In 1985, in a region over Antarctica, the yearly polar vortex had caused the ozone layer to deplete so greatly, that it could be classified as a hole. In 1996, this hole was large enough to cover Antarctica. The depletion of the ozone layer does not come without problems.

Scientific research has suggested the probability that increased UV-B radiation as a result of the thinning ozone layer leads to increased cases of skin cancer, immuno-suppression, cataracts, and ‘snowblindness’ due to radiation damage of the DNA. Additionally, experiments have shown a correlation between increased UV radiation and crop damage due to UV radiation damaging the plants’ DNA. Some scientists, however, feel that this will not be a problem in the future due to the possibility of breeding UV resistant crops and plants.

Many national governments and agencies recognized the problem of ozone depletion, and therefore, united in 1987 to sign the Montreal Protocol. This agreement was implemented to decrease CFC levels in order to help protect the thinning ozone layer. Clearly, ozone depletion is a dangerous problem due to possible disease outbreaks and famine as a result of increased UV-B radiation. However, society can collectively attempt to combat this problem by relatively simple means such as education and the practice of ‘ozone smart’ behavior.

For if society acts now, future generations will be handed a safe and healthy planet. Although the earth will be able to ‘heal’ itself if the CFC level continues to stay as it is, the depletion of the ozone layer is still a problem that society should be concerned with. In order for earth to repair the damage humans have posed on the ozone layer, society must take an active role. There are many tasks individuals can involve themselves in to help combat the problem of ozone depletion. First of all, one can simply check product labels for ozone friendly status.

Many companies have gone to great lengths to remove CFCs from their products. These products do not do as much damage to the ozone layer, and thus, are denoted as ‘ozone friendly. ’  A collaborative effort by society not using products with CFCs is a major step toward the healing of the ozone layer. Unfortunately, many products still used in society are detrimental to the ozone layer. When individuals must dispose of products with refrigerants in them, certain actions must be taken in order to prevent the CFCs from escaping from the disposed product.

For example, when an agency, such as a waste hauling company, comes to pick up the unwanted appliance, check to make sure refrigerant-recovery equipment is used by the agency. This equipment allows for the disposal of refrigerants without damage to the ozone layer. Society can also help the problem of ozone depletion through education, as well as through various donations. If individuals contribute time or money to environmental agencies focused on healing the ozone layer, the agencies will be able to organize activities promoting the understanding of the ozone problem.

If society is educated through these means, more individual efforts will be taken to make ‘ozone smart’ decisions such as using ‘ozone friendly’ products. Although thinning ozone may not directly affect the generation growing up today, future generations depend on the actions taken now. Thus, it is important for society to recognize that the thinning ozone layer is a problem and to take action in order to ensure the safety and survival of future generations. REFERENCES The Environmental Protection Agency http://www. epa. gov Environmental Protection Agency. ‘Disposing of Appliances With Refrigerants. Online. Internet. 22 Feb. 1998. http://earth1epa. gov/docs/region10/www/offices/air/disposal. html Environmental Protection Agency. “Ozone Depletion. ”  Online. Internet. 18 Feb. 1998. http://www. epa. gov/docs/ozone/index. html Environmental Protection Agency. “The Science of Ozone Depletion. ”  Online. Internet. 18 Feb. 1998. http://www. epa. gov/ozone/science/ Geocities. ‘Ozone Depletion. ’ Online. Internet. 9 Feb. 1998. http://www. geocities. com/RainForest/Vines/4030/index. html Goddard Distributed Active Archive Center. ?Atmospheric Structure.? Online. Internet. 20 March 1998. http://daac. gsfc. nasa. ov/CAMPAIGN_DOCS/ATM_CHEM/atmosphere_structure. html NOAA Aeronomy Laboratory. ‘Regions of the Atmosphere. ’ Online. Internet. 22 Feb. 1998. http://www. al. noaa. gov/WWWHD/AL images/regions. jpeg Ozone Action. ‘Health Effects of Ozone Depletion. ’ Online. Internet. 9 Feb. 1998. http://www. ozone. org/page5. html Ozone Action. ‘Ozone Depletion and Environmental Effects. ’ Online. Internet. 9 Feb. 1998. http://www. ozone. org/page12. html Ozone Depletion. 02 Jul, 2009 http://essaymania. com/133988/ozone-depletion Depletion Of The Ozone Layer. 02 Jul, 2009 http://essaymania. com/37144/depletion-of-the-ozone-layer


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