Term Paper: Ozone Depletion- Meaning, Causes and Reason | Environment

In this term paper we will discuss about the ozone depletion. After reading this term paper you will learn about:- 1. Introduction to Ozone Depletion 2. Meaning of Ozone Depletion 3. Occurrence 4. Distribution 5. Causes 6. Reasons 7. Harmful Substances 8. Effects 9. Impact 10. Prevention.

Term Paper on Ozone Depletion

Term Paper Contents:

1. Term Paper on Introduction to Ozone Depletion
2. Term Paper on the Meaning of Ozone Depletion
3. Term Paper on the Occurrence of Ozone Depletion
4. Term Paper on the Distribution of Ozone Depletion
5. Term Paper on the Causes of Ozone Depletion
6. Term Paper on the Reasons of Ozone Depletion
7. Term Paper on Harmful Substances that Lead to Ozone Depletion
8. Term Paper on the Effects of Ozone Depletion
9. Term Paper on the Impact of Ozone Depletion
10. Term Paper on the Prevention of Ozone Depletion

Term Paper # 1. Introduction to Ozone Depletion:

Ozone is a modified oxygen gas. Three oxygen atoms together constitute one molecule of ozone. The chemical formula is O₃. A dense ozone layer exists in the stratosphere zone, about 25 to 30 km. above the Earth surface. Ozone protects the earth from harmful ultraviolet rays from reaching in the atmosphere, which may cause skin cancer.

Ozone at the higher levels of the atmosphere, the stratosphere, is a product of UV radiation acting on oxygen (O₂) molecule. The higher energy UV radiations split apart some molecular oxygen (O₂) into free oxygen (O) atoms.

These atoms then combine with the molecular oxygen to form ozone as shown:

Chloro Fluoro Carbon (CFC), which is used in aerosol cans and fridges, ACs, is responsible for damaging the ozone layer. CFC remains in the atmosphere and reacts with the ultraviolet rays from sunlight, breaks itself and releases the chlorine.

The free chlorine then acts as a catalyst and breaks the ozone molecule to oxygen molecule and one oxygen atom. This process goes for years after years. Above Antarctica, ozone layer thinning was observed in 1985.

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Term Paper # 2. Meaning of Ozone Depletion:

The amount of damage that an agent can do to the ozone layer is expressed relative to that of CFC-11 and is called the Ozone Depletion Potential (ODP), where the ODP of CFC-11 is 1.

The lifetime of some of these ozone depleting substances is very long, and they may continue to deplete the ozone layer long after their use has been phased out. In this publication the ODP values for 100-year timespan are used. Nevertheless some shorter-lived substances may have a very high chlorine loading potential and thus their effect in the short term is much larger than reflected by their ODP value.

Aircraft emissions of nitrogen oxides and water vapour add to this depletion effect by creating ice crystals that serve as a base for ozone destroying reactions.

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Term Paper # 3. Occurrence of Ozone Depletion:

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 synthetic compounds are now accepted as the main cause of this depletion.

It was first suggested, by Drs. M. Molina and S. Rowland in 1974, that a man-made group of compounds known as the chlorofluorocarbons (CFCs) were likely to be the main source of ozone depletion. However, this idea was not taken seri­ously until the discovery of the ozone hole over Antarctica in 1985.

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 12(1 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 radiation, releasing free chlorine.

The chlorine becomes ac­tively involved in the process of destruction of ozone. The net result is that two molecules of ozone are replaced by three of molecular oxygen, leaving the chlorine free to repeat the process:

CI + O₃ → CIO + O₂

CIO + O → CI + O₂

Ozone is converted to oxygen, leaving the chlo­rine atom free to repeat the process up to 100,000 times, resulting in a reduced level of ozone. Bro­mine compounds, or halons, can also destroy stratospheric ozone. Compounds containing chlorine and bromine from man-made synthetic compounds are known as industrial halocarbons (Fig. 15.5).

Fig. 15.5: Ozone Layer Destruction

Global ozone levels have declined an average of about 3% between 1979 and 1991. This rate of decline is about three times faster than that re­corded in the 1970s. In addition to Antarctica, ozone depletion now affects almost all of North America, Europe, Russia, Australia, New Zealand, and a sizeable part of South America.

Short-term losses of ozone can be much greater than the long- term average. In Canada, ozone depletion is usually greatest in the late winter and early spring. In 1993, for example, average ozone values over Canada were 14% below normal from January to April.

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Term Paper # 4. Distribution of Ozone Depletion:

The distribution of ozone in the stratosphere is a function of altitude, latitude and season. It is determined by photochemical and transport processes. The ozone layer is located between 10 and 50 km above the Earth’s surface and contains 90% of all stratospheric ozone. Under normal conditions, stratospheric ozone is formed by a photochemical reaction between oxygen molecules, oxygen atoms and solar radiation.

Measurements carried out in the Antarctic have shown that at certain times, more than 95% of the ozone concentrations found at altitudes of between 15 and 20 km and more than 50% of total ozone are destroyed, with reductions being most pronounced during winter and in early spring. Natural phenomena, such as sun-spots and stratospheric winds, also decrease stratospheric ozone levels, but typically not by more than 1-2%.

The main cause of ozone layer depletion is the increased stratospheric concentration of chlorine from industrially produced CFCs, halons and selected solvents. Once in the stratosphere, every chlorine atom can destroy up to 100 000 ozone molecules.

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Term Paper # 5. Causes of Ozone Depletion:

Scientific evidence indicates that stratospheric ozone is being destroyed by a group of manufactured chemicals, containing chlorine and/or bromine. These chemicals are called “ozone-depleting substances” (ODS).

ODS are very stable, nontoxic and environmentally safe in the lower atmosphere, which is why they became so popular in the first place. However, their very stability allows them to float up, intact, to the stratosphere.

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. A single molecule of chlorine can break apart thousands of molecules of ozone.

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Term Paper # 6. Reasons of Ozone Depletion:

(i) The balance has been disrupted due to enhancement of ozone degradation by chlorofluorocarbons (CFCs).

(ii) CFCs are widely used as refrigerants. When they are discharged in the lower part of atmosphere, they move upward and reach the stratosphere.

(iii) In stratosphere, UV rays act on them releasing CI atoms.

(iv) CI degrades ozone releasing molecular oxygen.

(v) CI atoms are not consumed in the reaction. Hence, once CFCs are added to the stratosphere, they have permanent and continuous effects on ozone levels.

Harmful Effects of UV Rays:

i. DNA and proteins of living organisms preferentially absorb UV rays and its high energy breaks the chemical bonds within these molecules.

ii. UV-B damages DNA and causes mutation.

iii. Damage to the skin cells.

iv. Ageing of the skin.

v. Various types of cancers.

vi. Inflammation of the cornea, i.e., snow blindness.

vii. Cataract.

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Term Paper # 7. Harmful Substance that Leads to Ozone Depletion:

Some harmful substances of ozone depletion are as follows:

i. Chlorofluorocarbons:

Chlorofluorocarbons or CFCs (also known as Freon) are non-toxic, non-flammable and non-car­cinogenic. They contain fluorine atoms, carbon atoms and chlorine atoms. The five main CFCs in­clude CFC-11 (trichlorofluoromethane-CFCl₃), CFC-12 (dichlorodifluoromethane-CF₂Cl₂), CFC-113 (trichlorotrifluoroethane-C₂F₃Cl₃), CFC-114 (dichlorotetrafluoroethane-C₂F₄Cl₂), and CFC-115 (chloropentafluoroethane-C₂F₅Cl).

ii. Hydro Chlorofluorocarbons:

Hydro chlorofluorocarbons or HCFCs contain chlorine but, unlike CFCs, they also contain hy­drogen (the H) which causes them to break down in the lower atmosphere (troposphere). They are called transition chemicals because they are con­sidered an interim step between strong ozone depletes and replacement chemicals that are en­tirely ozone-friendly.

Unfortunately, like CFCs, they are strong greenhouse gases and contribute to­wards global warming.

iii. Carbon Tetrachloride:

Carbon tetrachloride (CCl₄), despite its toxicity, was first used in the early 1900s as a fire extinguishing, and more recently as an industrial solvent, an agri­cultural fumigant, and in many other industrial processes including petrochemical refining, and pesticide and pharmaceuticals production.

Recently it has also been used in the production of CFC-11 and CFC-12. It has accounted for less than 8% of total ozone depletion. The use of carbon tetrachloride in developed countries has been pro­hibited since the beginning of 1996 under the Montreal Protocol.

iv. Methyl Chloroform:

Methyl chloroform, also known as 1, 1, 1 trichloroethane is a versatile, all-purpose industrial solvent used primarily to clean metal and electronic parts. It was introduced in the 1950s as a substi­tute for carbon tetrachloride. Methyl chloroform has accounted for roughly 5% of total ozone depletion.

The use of methyl chloroform in de­veloped countries has been prohibited since the beginning of 1996 under the Montreal Protocol.

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Term Paper # 8. Effects of Ozone Depletion:

Some of the effects of ozone depletion are as follows:

i. Ozone Depletion and Skin Cancer:

The most well-known effect of UV radiation is the slight reddening or burning of the skin in sun­shine. This change of colour is caused by an ex­pansion of the skin’s blood vessels. For most people burning is followed by tanning within a couple of days. A permanent tan will occur when the UV radiation causes a pigment called melanin to form in the pigment cells of the skin.

Over a period of years, exposure to radiation originating from the Sun causes damages in the skin’s con­nective tissues, so-called photo-ageing. This shows itself as a thickening of the skin, as wrinkles and decreasing elasticity. Elastine and collagen fibres determining the firmness and elasticity of the skin are damaged. UV radiation increases the risk of getting skin cancer.

Research has shown that even small amounts of UV-B radiation can cause considerable harm. UV-B damages the genetic material of DNA and is related to some types of skin cancer. It is im­portant to note, however, that UV-B radiation has always had this effect on humans. In recent years non-melanoma skin cancer has become more prevalent in many parts of the world because people are spending more time in the Sun and are exposing more of their skin in the process.

The relationship between the occurrence of milder non-melanoma skin cancers and time spent in the Sun is well documented. Such cancers gen­erally occur in people in their 70s and 80s on areas of the skin usually exposed to sunlight (such as the face or hands). Malignant melanoma, however, usually occurs in younger people and in skin areas not necessarily exposed to sunlight.

It tends to occur most commonly among groups of people less likely to have spent significant amounts of time outdoors. Ozone in the stratosphere protects Earth from damaging amounts of ultraviolet (UV) radiation. A depleted ozone layer would allow more of the Sun’s rays to reach Earth’s surface.

An in­crease in the levels of UV-B reaching the Earth as a result of ozone depletion may compound the effects of spending more time in the Sun. Accord­ing to some estimates a sustained 10% global loss of ozone may lead to a 26% increase in the inci­dence of skin cancers among fair skinned people.

The US Environmental Protection Agency esti­mates that a 2% increase in UV-B radiation would result in a 2 to 6% increase in non-melanoma skin cancer. Increases in UV radiation relative to levels in the 1970s are estimated to be as much as 7% at Northern Hemisphere mid-latitudes during the winter and spring, 4% at Northern Hemisphere mid-latitudes in summer and autumn, and 6% at Southern Hemisphere mid-latitudes on a year- round basis.

Australia, with high sunshine levels, has very high skin cancer rates. An estimated 2 out of ev­ery 3 people in most parts of the country will de­velop some form of skin cancer. In Queensland, where UV-B radiation is the highest, the probabil­ity jumps to 3 in every 4.

In America, in 1935, the chances of developing the more serious malignant melanoma was 1 in 1500. In 1991 it had soared to 1 in 150, and it is predicted that by the beginning of the new millennium it will be 1 in 75.

ii. Ozone Depletion and Eye Disorders:

As the ozone layer gets thinner, UV-B radiation at the surface of the Earth increases. If the ozone amount decreases by 10% during the spring and summer, the annual UV dose increases by about 12%. Cataracts and blindness are among the most common eye diseases associated with further ozone layer depletion and increased UV-B at the Earth’s surface.

Unlike the skin, which can adapt to UV radiation by becoming browner and thicker, the eye does not have any such defence mechanisms. On the contrary, research shows that eyes become more sensitive with increased exposure to radiation. This can damage the cornea, the lens and the retina.

Increased exposure to UV radiation from ozone depletion is expected to increase the num­ber of people experiencing cataracts. A 1% de­crease in stratospheric ozone may result in 100,000 to 150,000 additional cases of blindness due to eye cataracts world-wide.

iii. Ozone Depletion and the Immune System:

Scientific research suggests that sunburn can alter the distribution and function of disease-fighting white blood cells in humans for up to 24 hours after exposure to the Sun. In addition, repeated exposure to UV radiation may cause more long-lasting damage to the body’s immune system.

Whilst little research has been conducted on the effects of decreasing stratospheric ozone on hu­man immunity, it is likely that continued destruc­tion of the ozone layer will lead to further health complications, in addition to skin cancers and eye disorders, as a result of the suppression of our ability to fight off disease.

iv. UV-B AND Marine Organisms:

Plankton form the foundation of aquatic food webs. Plankton productivity is limited to the euphotic zone, the upper layer of the water column in which there is sufficient sunlight to support the photosynthesis of food.

Since UV radiation has the ability to penetrate up to 20 metres down in clear water, plankton and other light dependent organisms often experience cell damage, much as human DNA can be damaged by the strong solar radiation. Both plant (phytoplankton) and animal (zooplankton) species are damaged by UV-radiation even at current levels.

As with certain land plants, some species are more sensitive to UV-light at critical stages in their life cycle, and changes in radiation may shorten the breeding period to in­tolerable levels.

As plankton make up the base of the marine food chain, changes in their number and species composition will influence fish and shellfish production world-wide. These kinds of losses will have a direct impact on the food sup­ply.

Solar UV-B radiation has also been found to cause damage to the 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 UV-B radiation is a limiting factor, and small increases in UV-B exposure could result in a significant reduction in the size of the population of animals that eat these smaller creatures.

v. UV-B and Land Plant/Vegetation:

Exposure to UV-B radiation may have a dramatic effect on terrestrial plant life, although the impacts are at present poorly understood. Absorption of UV radiation varies widely from one organism to the next. In general, UV radiation deleteriously affects plant growth by reducing leaf size and lim­iting the area available for energy capture during photosynthesis.

Plant stunting and a reduction in total dry weight are also typically seen in UV-irra­diated plants, with a reduction in the nutrient con­tent and the growth of the plants, especially in the legume and cabbage families.

A reduction in qual­ity of certain types of tomato, potato, sugar beet and soya bean has also been observed. Forests also appear to be vulnerable. About half of the spe­cies of conifer seedlings so far studied have been adversely affected by UV-B at a variety of levels.

Although old needles are able to protect them­selves by strengthening their outer wax coating and by increasing the amount of protective pigment, young growing pine needles, in contrast, suffer easily.

Indirect changes caused by UV-B radiation (such as flowering and germination rates, changes in plant form and how nutrients are distributed within the plant) may be more important than dam­aging effects of the radiation itself. These changes can have important implications for plant com­petitive balance, plant diseases, and biogeochemical cycles.

However, reliable scientific information on the effects of UV on plants is limited. Only four out of 10 terrestrial plant ecosystems (tem­perate forest, agricultural, temperate grassland, and tundra and alpine ecosystems) have been studied. In addition, much of the existing data come from greenhouses where plants are more sensitive to UV-B than those grown outdoors.

There are indi­cations that some weeds are more UV-B resistant than crops. Many organisms have developed mechanisms for protecting themselves from UV- B for examples by avoiding exposure, shielding themselves with pigment and repairing damaged DNA or tissue damage.

vi. Damage to Polymers:

Ozone depletion will cause many materials to de­grade faster. These materials include PVC (used in window and door frames, pipes and gutters, etc.) nylon and polyester. They are all composed of compounds known as polymers. 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 UV-B by special additives. Therefore, any increase in solar UV-B levels as a result of ozone depletion will therefore accelerate their breakdown, limiting how long they are useful outdoors. Shorter wavelength (i.e. more energetic) UV-B radiation is mainly re­sponsible for photo-damage ranging from discol­oration to loss of mechanical integrity in polymers exposed to solar radiation (Fig. 15.9).

The use of higher levels of conventional light stabilisers in polymer-based materials are likely to be employed to mitigate the effects of increased UV levels in sunlight. However, it is not certain how resistant such light stabilisers are themselves to increased levels of UV-radiation.

In addition, their use will add to the cost of plastic products in target applications. With plastics rapidly displac­ing conventional materials in numerous applica­tions, this is an important consideration particu­larly in the developing world. It is not certain yet how other materials, in­cluding rubber, paints, wood, paper and textiles will be affected by increased UV radiation result­ing from ozone depletion.

vii. Effects on Biogeochemical Cycles:

Increases in solar UV radiation could affect ter­restrial and aquatic biogeochemical cycles, thereby 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. Likely effects include an increase in smog in urban centres, and acid rain in rural areas.

viii. Effects on Climate:

Whilst increases of UV radiation as a result of ozone depletion may affect the production and removal of carbon dioxide, the main greenhouse gas, ozone depletion itself can influence the global climate. Ozone is also a greenhouse gas, and as well as fil­tering out the incoming short-wave solar radiation, can absorb much of the outgoing long-wave ter­restrial radiation (infrared radiation).

If stratospheric ozone is destroyed, ozone’s greenhouse effect is reduced and this could lead to a global cooling, off­setting some of the warming that may be occurring as a result of man-made emissions of CO₂, CH₄, NO_X. Ironically, when the ozone layer starts to re­pair itself in the next century as a result of a con­trol on CFC, this cooling potential will be lost.

More significantly, the replacement chemicals to CFCs, the HCFCs, which themselves do not harm the ozone layer, are strong greenhouse gases, and the further contributing to the potential problem of global warming (Fig. 15.10).

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Term Paper # 9. Impacts of Ozone Depletion:

Stratospheric ozone filters out most of the sun’s potentially harmful shortwave ultraviolet (UV) radiation. If this ozone becomes depleted, then more UV rays will reach the earth.

Exposure to higher amounts of UV radiation could have serious impacts on human beings, animals and plants, such as the following:

i. Harm to Human Health:

a. More skin cancers, sunburns and premature aging of the skin.

b. More cataracts, blindness and other eye diseases- UV radiation can damage several parts of the eye, including the lens, cornea, retina and conjunctiva.

c. Cataracts (a clouding of the lens) are the major cause of blindness in the world. A sustained 10% thinning of the ozone layer is expected to result in almost two million new cases of cataracts per year, globally.

d. Weakening of the human immune system (immunosuppression). Early findings suggest that too much UV radiation can suppress the human immune system, which may play a role in the development of skin cancer.

ii. Adverse Impacts on Agriculture, Forestry and Natural Ecosystems:

a. Several of the world’s major crop species are particularly vulnerable to increased UV, resulting in reduced growth, photosynthesis and flowering. These species include wheat, rice, barley, oats, corn, soybeans, peas, tomatoes, cucumbers, cauliflower, broccoli and carrots.

b. The effect of ozone depletion on the Canadian agricultural sector could be significant.

c. Only a few commercially important trees have been tested for UV (UV-B) sensitivity, but early results suggest that plant growth, especially in seedlings, is harmed by more intense UV radiation.

iii. Damage to Marine Life:

a. In particular, plankton (tiny organisms in the surface layer of oceans) are threatened by increased UV radiation. Plankton are the first vital step in aquatic food chains.

b. Decreases in plankton could disrupt the fresh and saltwater food chains, and lead to a species shift in Canadian waters.

c. Loss of biodiversity in our oceans, rivers and lakes could reduce fish yields for commercial and sport fisheries.

iv. Animals:

In domestic animals, UV overexposure may cause eye and skin cancers. Species of marine animals in their developmental stage (e.g. young fish, shrimp larvae and crab larvae) have been threatened in recent years by the increased UV radiation under the Antarctic ozone hole.

v. Materials:

a. Wood, plastic, rubber, fabrics and many construction materials are degraded by UV radiation.

b. The economic impact of replacing and/or protecting materials could be significant.

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Term Paper # 10. Prevention of Ozone Depletion:

The nations of the world have taken a crucial step in joining together to halt the production and use of ozone-destroying chemicals. But the work can’t stop there.

To prevent the further depletion of Ozone layer, we can take the following precautionary steps:

i. Awareness Know the rules it is illegal to recharge refrigerators, freezers and home/vehicle air conditioners with CFCs.

ii. If you have an older vehicle with an air conditioner, have it serviced by a qualified technician, and make sure the CFC is recaptured and recycled by technician who is specifically certified to do this work. If you don’t use your air conditioner — or if the vehicle is about to be scrapped — make sure a qualified technician recaptures and recycles the CFC. The same rules apply to older refrigerators freezers and home air conditioners, which may contain CFCs.

iii. Don’t buy or use portable fire extinguishers that contain halons.

Montreal Protocol International treaty signed in the 1987 to control the emission of chlorine emitting substances. After Montreal, many other protocols have been signed to control the emission of CFCs and other ozone depleting substances. Similar more protocols have been laid down in controlling emission of CFCs and other ozone depleting chemicals.

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