A Research Paper On The Ozone Depletion, Its History, Consequences, And Solutions

Introduction

The Earth’s atmosphere consists of 5 layers. They stretch from the surface up. The ozone (O3) resides in the stratosphere which is from the surface of the earth up 50 kms. 10% of the ozone is in the troposphere. This only stretches from the Earth’s surface 16kms up. Ozone is quite harmful to the humans living on earth if breathed in. Things such as eye infection, asthma, increased risk of infection and compromised lung function can occur as a result. The ozone plays a key part for our world protecting us from the extreme ultraviolet light the sun produces. It absorbs the UV light in order for us to avoid skin cancer and genetic issues. Though this is now become less possible as through human harm we have depleted the density of the ozone layer and so therefore our protection is lessened.

History

The ozone depletion is a result of majority man-made damage. We have introduced gases and chemicals through the evolution of our lives and our advance in technology’s. Especially our supersonic air travel. Nitric oxide (NO) has been known to catalytically react with the ozone (O3) to produce O2. This was not an issue as the NO molecules at ground level have a short life and never made it up into the stratosphere. Though through the introduction of supersonic commercial jets that fly up in the stratosphere, NO molecules are now directly deposited into the stratosphere to react with the ozone and produce O2 molecules. In 1974 Sherwood Rowland and Mario Molina discovered that chlorofluorocarbons could be photolyzed by high energy photons in the stratosphere. This means the chlorofluorocarbons are broken up by the high energy photons which are packages of light. Ozone density is measured in Dobsen units, 1 Dobsen unit represents 1 molecule of O3 for every 1 billion air molecules. This has been recorded at its thinnest over Antarctica, and here is often referred to as the “ozone hole. ” Therefore, in New Zealand we have such harsh sun because we are reasonably close to Antarctica in relation.

The Chapman Cycle

The stratosphere is in a constant cycle. This is because oxygen molecules and UV rays are constantly in contact with each other in the stratosphere. When an oxygen molecule reacts with UV rays it produces ozone and oxygen radicals. This is considered cycle because the ozone is constantly being created and destroyed and can have very varied density at any point in time. This is a natural cycle that has been taking place for years. Because O2 is constantly being produced as a result of photosynthesis and so therefore the ozone layer can reproduce itself. Step 1: An oxygen molecule is photolyzed by solar radiation, creating two oxygen radicals: hν+O2(g)→2O(g) Step 2: Oxygen radicals then react with molecular oxygen to produce ozone: O2(g)+O(g)→O3(g) Step 3: The ozone molecule that is produced then reacts with an additional oxygen radical to form molecular oxygen: O3(g)+O→2O2(g) Step 4: Ozone can also be recycled into molecular oxygen by reacting with a light photon: O3(g)+hν→O2(g)+O(g)

Ozone Depletion Chemistry

There are lots of man-made chemicals that can be made responsible for the thinning of our ozone layer. These are all categorized into groups and the extent of their effect on the ozone layer. Two of the main ones which are blamed most often are chlorofluorocarbons (CFC’s) and Bromotrifluoromethane, also known as halon 1301. These two are in different groups. Chlorofluorocarbons are made up of carbons, fluorine and chlorine. Bromotrifluoromethane is made up of bromine, three fluorine and carbons. The trouble causing this damage is chlorofluorocarbons in our atmosphere. They originate from our everyday lives in things such as refrigerators, air-conditioning, aerosols and other foam material. They are extremely stable. Meaning they are very hard to destruct and are also not water soluble and so don’t dissolve in the rain either. This stability is what allows them to last for such prolonged periods in our atmosphere. This means they can move from the troposphere to the stratosphere, where most molecules would decompose before they made the transition. They can get to altitudes where photons become much more energetic. This means that when these chlorofluorocarbons encounter the highly energized photons, the chlorine atom becomes freed from the rest of the molecule and becomes the reason for the ozone depletion. Bromotrifluoromethane is also responsible for ozone depletion though is much less commonly used worldwide and so although it is much more damaging to the ozone layer it only accounts for approximately 20% of the depletion recorded. Halon 1301 is also used as a refrigerant but more commonly in fire suppression. It is extremely toxic for humans, even more so than the chlorofluorocarbons. It can affect our nervous system and other bodily functions. Like the chlorofluorocarbons the halon 1301 is extremely stable and so can work its way up into the stratosphere in just the same way. Until it reaches the ozone layer where it can then be broken down/photolyzed by the photons of UV light. The chlorine and bromine atoms are able to destroy as many ozone molecules as they like because they are catalyst. This means they are able to be used in a reaction without being used up. It initiates the reaction with the ozone and then combines with freed oxygen atoms to create two oxygen molecules. Then after its reacted with one ozone molecule, because it’s a catalyst it then can go and repeat the process with another ozone molecule. This means for everyone chlorofluorocarbon that reaches the stratosphere, thousands of ozone molecules are destroyed. Though the ozone is a cycle and can reproduce, it is currently getting destroyed faster than it can be reproduced. This then leads to a less dense ozone layer, meaning less ultra-violet light rays can be absorbed. We therefore, experience a more intense version of the sun.

Consequences on humans

With the depletion of the ozone layer in the stratosphere less UV light is able to be absorbed, particularly UV-B rays. This means more of the suns UV-B rays reach the surface of the earth and so we are exposed to this. Labatory and epidemiological studies have shown that the UV-B rays from the sun are known to cause non-melanoma skin cancer and is a big part in the development of malignant melanoma. These UV-B rays have also been linked to cataracts. Melanoma is the most dangerous form of skin cancer. Though it is not the most common kind of skin cancer it causes over 75% of skin cancer deaths each year. It is most common in adolescents aged between 19 and 29. The cause is often sun related, though not always. It can be a result of constant exposure to UV light and reoccurring sunburn, especially as a child. Melanoma can also be a result of genetic faults and immune system deficiencies. Non-melanoma skin cancer though not as severe, if untreated can spread and cause health problems and misshaping. There are two types of this condition: Basal cell carcinomas and squamous cell carcinomas. Basal cell carcinomas are the most common type of skin cancer tumor. It often appears in bumps on the face or neck but can be other places on the body. It rarely spreads and they grow relatively slowly. But they can penetrate the bone, which causes significant damage. Squamous cell carcinomas appear in large red patches or nodules. They, unlike, basal cell carcinomas spread to other parts of the body and can develop into large masses. Exposure to the UV-B rays from the sun also leads to cataracts. This is a loss of clarity in the eyes lens and so it seems there is a cloudy filter over everything the patient sees. Although curable with the modern-day eye surgery, it is an expensive and risky process. There are also other eye diseases related to sun exposure including: pterygium, skin cancer around the eyes and degeneration of the macula. Scientists have also found that over exposure to UV rays may lead to a compromised immune system and the skins natual defense mechanism. For example, our skin is supposed to naturally form a defense to invaders such as skin cancers and infections. But with overexposure in UV radiation it weakens the immune system, and therefore cannot provide this protection.

Consequences on the environment

Plants

The UV-B rays from the sun affect the physiological and developmental processes of plants living on earth. Although we as humans have tried ways of preventing and fixing this; and the pants have the ability to adapt to cope in increased UV radiation, it still directly effects their growth. Indirectly plants, their form, nutrient distribution, development processes and secondary metabolism can be affected. These changes can be equally if not more dangerous to the plants. These can change important balances within the plant, that leads to disease.

Marine life

Phytoplankton is the main source of food for aquatic animals. The phytoplankton productivity is limited to the euphotic zone. This is the top layer of the oceans water where there is the correct amount of sunlight in order for the production of phytoplankton to thrive. With an increase in UV-B light rays penetrating through the atmosphere to earth the radiation is affecting the phytoplankton's ability to move and orientate themselves. This means the supply is diminishing as what scientists have proven to a direct link of the depleted ozone layer. Effects have been seen with other marine life such as fish, crabs, amphibians. The most extreme cases ending in impaired reproductive capacity and impaired larval development. With a small increase in UV-B exposure the populations of small breeds could be threatened by extinction. This would lead to trouble within the whole marine food chain.

Solutions

The only real solution for this depletion of the ozone layer is to fade out the use of chlorofluorocarbons and bromotrifluoromethane. We can begin to do this by replacing some of them with hydrofluorocarbons. These synthetically produced organic compounds are made up of hydrogen, fluorine and carbon. They contain a hydrogen atom and so a C-H bond which makes them less stable. This means that the hydrofluorocarbons aren’t able to make it to the stratosphere, because they are reactive enough that they react with hydroxyl radicals in the troposphere. Because the hydrofluorocarbons don’t make it to the stratosphere, they can't cause any damage to the ozone layer. When the hydrofluorocarbons react with the hydroxyl radicals' water is a byproduct. The problem that arises when replacing chlorofluorocarbons with hydrofluorocarbons is that hydrofluorocarbons are a greenhouse gas. Though this is a solution to one environmental problem, the depleting ozone layer, it has a consequence that comes with it. When the carbon, fluorine bond absorbs the suns radiation and reflects it back towards the earth’s surface, contributing to global warming. Hydrofluorocarbons are a much worse pollutant than the traditional greenhouse gases such as carbon dioxide. So, although not too many hydrofluorocarbons are currently released, we need to be careful that we don’t make one issue worse as we fix the other. Changes that we can personally make to try and protect our ozone from further depletion could be: Don’t buy Aerosole cans. Whether it be deodorant, paint, or any other form of spray can. Dispose carefully and properly of old fridges and air conditioning units that may be using CFC’S as a cooler. Make sure it is disposed of correctly though in order to avoid further releases of the chemicals. Also, buy fire extinguishers that do not contain Halons but use a foam instead. Living in New Zealand it becomes common knowledge to wear sunscreen in summer because of our intensive sun. This is because of the depleted ozone layer, or the hole. The hole spreads mostly over Antarctica but because we are relatively close to Antarctica, we experience the effects of it. Sunblock acts almost as a mini ozone layer. We apply it to our skins surface that is exposed to the UV-B rays in order to form a layer of protection from their harm. It contains inorganic chemicals such as zinc oxide or titanium oxide. These physically reflect the UV-B rays' kind of like white paint. And hence the white colour of sunblock because of these chemicals. Also, there are some organic chemicals such as avobenzone and oxybenzone. These work in a different way by absorbing the UV radiation through their chemical bonds. This breaks down the components o the sunscreen until it becomes ineffective. Therefore, it is always important to remember to keep reapplying your sunscreen throughout the day.

The Montreal Protocol

Tthis is a treaty designed to prevent the depletion of the ozone layer. They intend to do this by fading out the use and production of the chemicals believed to be thinning the ozone layer. It was s initially opened for signature on the 16th of September 1987 and then entered on the 1st of January 1989. It has since undergone 5 revisions. The Montreal Protocol required that all production of new Halon was stopped by the 1st January 1994 and recycled Halon and inventories produced before this date where simply sources of supply.

References

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