The sun. This radiation is the one which
The beginning of the CFC(chlorofluorocarbons) era started in 1928, when CFC’ were invented by a Du Pont chemist. CFC’ were best known as “freons” and became famous as a safe, nonflammable refrigerant. It’s invention became a great triumph when Freon took the place of sulfur dioxide or ammonia which was used as the working liquid in refrigerators. It eventually became widely used in automobile air conditioners and nontoxic propellants in aerosol cans.
It’s insulating properties also was used for blowing agents for plastics and foam cups.Thus CFCs became used all over the world and its business got bigger and bigger until late in 1973. Sherwood Rowland and Mario Molina, two distinguished chemists, came up with a surprising result in his calculations concerning the CFCs and ozone layer.
CFCs are basically inactive in the troposphere(around the altitude of 50,000 feet) so it would gradually drift upward until they reached the mid-stratosphere.(about 100,000 feet) At this point CFCs would be broken down by short-wavelength ultraviolet radiation from the sun. This radiation is the one which would not reach the lower atmosphere in large amounts because of the ozone layer. When these CFCs do brake down, they released atomic chlorine which then would react with the ozone and convert it back into plain oxygen. The even worse part of all this is that these chlorine molecules do not become inactive after the first reaction with the ozone and would be available to destroy more ozone molecules. Thus this process would be the function of a catalyst; a single chlorine atom involved in a chain reaction to destroy many ozone molecules. Rowland and Molina eventually agreed that this thinning of the ozone shield can cause a catastrophe for Earth’s living beings, including humans, by allowing large amounts of the deadly ultraviolet-B radiation to reach to Earth’s surface.
Rowland and Molina checked their calculations again and again to make sure that these figures had not a single mistake in it because this conclusion was likely to destroy an $8 billion industry already in the United States. However, the lives of the living beings were far more important than businesses so in 1974 Rowland and Molina, having their calculations checked by their colleagues, explained their theory in a paper in the eminent scientific journal Nature. Later the only reasonable conclusion they drew out was that the use of CFCs be banned.
When these calculations were released to the public, Du Pont, the major CFC manufacturer, did everything they can to convince the people that the calculations were unproven and theoretical. However Rowland and Molina did a marvelous job of defending their results and explaining the significance of these dangerous CFCs to other scientists, government officials, and the press. Eventually the CFC use in aerosols was banned in the US in 1978. However the total ban of the use of CFCs was almost impossible for Rowland and Molina due to scientific confusion and the arrival of the antienviornmental Reagan administration. Another problem that they soon realized was that for example if a total ban of CFCs is achieved by the year 2000, the atmosphere would still contain more CFCs in the year 2000 than it does today, and 90% of the CFCs in the air when the ban comes into effect will still be there in 2010. So in the end “the worldwide depletion of the Ozone will get worse before it gets better.”The Dangers and Costs of Ozone DepletionThe public realized that the calculations of Rowland and Molina were absolutely correct at the end of the 1980’s and in the early 1990’s when large holes in the ozone layer began appearing around the world, especially over Antarctica.
It appeared that for every molecule of chlorine some 10,000 to 100,000 ozone molecules were being destroyed. Adding to that depletion can also be caused by bromine, a close chemical relative of chlorine, which can reach the stratosphere carried by chemicals called halons; however significantly in lesser amounts compared to CFCs. It was clear that the amount of ozone in the Northern Hemisphere stratosphere fell by 8 percent between 1979 and 1990, across a region that covers virtually all of the contiguous Untied States and Europe from the Mediterranean to the south of England. The results of the ozone depletion is very costly, especially to the human health. UV-B radiation was a proven cause of skin cancers and the disappearing ozone would significantly increase in skin cancer patients. For a rough estimate a 10% reduction in the ozone layer would result in 160,000 additional cases of nonmelanoma skin cancers annually. Although many types of skin cancers are not usually life threatening, Melanomas, which is rarer is often fatal.
Causes of this type of cancer is not exact but strongly associated with dangerous patterns of UV exposure such as getting heavily burned or tanned during rare vacations.Other diseases caused by UV exposure are Cataracts, which is the clouding of then lens of the eye, and the suppression of the immune response through the exposure of the skin and blood. This would result in increased vulnerability to serious diseases such as leishmaniasis, measles, herpes, TB, and leprosy. Immune suppression can cause a person to become seriously ill and even become fatal with mild illnesses, similar to the effects of AIDS on its patients.Other than the health threats to humans, UV radiation puts many other living organisms in danger. Two thirds of the over 200 types of plants tested became known to be sensitive to UV-B.
Effects in these plants include reduced stem and leaf growth, lower dry weight, and reduced photosynthetic activity. Many crops would also suffer because of nitrogen deficiencies, due to the sensitivity that microorganisms such as cyanobacteria(which fixes the nutrients) to UV-B. In short the effects of UV-B has been detected all over the world in all kinds of environments, even 60 feet under clear water which hurts many types of fish, mollusks, and most importantly phytoplankton. Destruction of these phytoplanktons would give serious problems to fishes which depend on these small creatures for food, and eventually effect humans. Global warming can also be caused by the reduction of phytoplanktons, because absorption of CO2 would be significantly reduced.