Реферат: Ozone Depletion Essay Research Paper Atmospheric ozone
Ozone Depletion Essay, Research Paper
Atmospheric ozone layer depletion is a serious problem currently facing the world. The ozone layer protects humans, animals, and plants from harmful ultraviolet rays. Money and time are being spent on ozone repair, but the problem still exists.
The ozone layer is a region of the stratosphere containing ozone, or O3 gas. The ozone layer is essential to both plant and animal life on earth because it protects the surface from dangerous ultraviolet light.
However, industrial and domestic chemicals that are currently in use have been found to destroy ozone, and the problem has escalated to an ozone layer “hole” above Antarctica. Ozone levels there are 40 percent below normal, and there may be another ozone hole forming above the Arctic region.1
Ozone gas contains an extraneous oxygen atom in each molecule and is highly unstable. This property lets ozone block out ultraviolet rays and makes it an essential part of the eco-system. When harmful ultraviolet-B rays (wavelength 240-320 NM) come through the atmosphere, the O3 molecules absorb the energy and one oxygen atom detaches from the molecule. The stray atom will eventually collide with another O2 molecule and ozone will be reformed. With this process, the level of ozone remains constant, as it has for millions of years.3
Recently, a number of chemicals have been found to aid in the rapid destruction of ozone. Most of these chemicals are compounds called chlorofluorocarbons, or CFC’s. It is difficult to ban them outright because they have hundreds of industrial uses. CFC’s are widely used because they are non-toxic, non-flammable, and inexpensive. Recent environmental legislation on both the state and national levels has banned the use of some CFC’s, but the question of their disposal still remains.4
Chlorofluorocarbons do not destroy ozone directly. Compounds made from CFC’s photo-decay series act as catalysts in the splitting of O3 molecules. When CFC’s reach the stratosphere, they break down when struck by the intense light rays. The molecule splits and a majority of the chlorine then forms hydrogen chloride or chlorine nitrate, which then decay into atomic chlorine or chlorine monoxide.3
These are the substances responsible for the physical destruction of ozone. As they come in contact with an ozone molecule, they cause the third oxygen atom to detach and form an O2 molecule with another stray oxygen atom. Since they don’t react with the oxygen, the chlorine compounds remain intact and can destroy up to 150,000 ozone molecules each.3
There are a number of different CFC’s. The compounds most responsible for ozone layer destruction are CFC-11 (trichlorofluoromethane), CFCl3; CFC-12 (dichlorodifluoromethane), CF2Cl2; and CFC-113 (1,1,2 trichlorotrifluoroethane), CF2ClCFCl2. All of these compounds are excellent refrigerants, and CFC-12 is marketed by DuPont as Freon™.3
The word “CFC” has become a generic term referring to any substance that is deleterious to the ozone layer. However, many destructive compounds are not CFC’s by definition. All ozone-destroying compounds contain at least one of two common elements: chlorine, or the more catalytic bromine. Compared atom-to-atom, bromine can destroy 10-100 times the number of ozone molecules as chlorine. Fortunately, its atmospheric concentration is much smaller.3
One of the other O3-destructive groups is called the hydrochlorofluorocarbons, or HCFC’s. HCFC’s are organic compounds in which not all of the hydrogen atoms have been replaced by chlorine or fluorine. One such compound is R-22 (HCFC-22), CHClF2.3
Some other non-CFC compounds that destroy the ozone layer include carbon tetrachloride (tetrachloromethane), CCl4; methyl chloroform (1,1,1 trichloroethane), CH3CCl3; and methyl chloride (chloromethane), CH3Cl.3
The result of ozone layer depletion is a increase in ultraviolet rays at the surface. Humans, animals, marine life, and plants are all susceptible to UV radiation damage.
Current studies indicate that ultraviolet rays could be disastrous to the marine eco-system. High UV concentration causes phytoplankton, microscopic organisms at the base of the food chain, to decrease their reproductive activity. Although there is no serious widespread effect now, the problem may escalate in future years.3
Numerous studies have proven that ultraviolet radiation, in both the UV-A and UV-B forms, causes skin cancer. Of the three types of skin cancer, basal cell carcinoma, squamous cell carcinoma, and melanoma, 90 percent of all cases can be attributed to overexposure to UV rays. Other effects of increased ultraviolet exposure, including sterility and cataracts, are currently under investigation.3
Ultraviolet radiation has effects on plants as well, though different species react in different manners. In a recent study of 200 plants, one variety of soybean plant showed a 25 percent reduction in growth when exposed to large amounts of UV rays. However, other types of soybean in the same study were not affected. It is estimated that a reduction in ozone level as little as 10 percent could seriously damage the world’s agricultural production.3
The ozone layer is a complex problem since the atmosphere is constantly shifting and diffusing. Many quick-fix theories exist, such as flying planes filled with ethane and propane over the Antarctic region. When the planes release the gasses, they would react with the harmful chlorine compounds and reduce their destructive power. However, the environmental effects could be devastating and it would be a complex and costly project.2
Another radical approach to CFC elimination is the use of lasers. Thomas Stix, a Princeton University physics professor says that lasers tuned to the right frequency can break CFC’s apart without affecting other atmospheric gasses. The disadvantage is the cost, which would be roughly 10 billion dollars a year in electricity.2
With ozone cleaning proposals being submitted and rejected on a daily cycle, many environmentalists believe that the earth will repair itself if CFC production comes to a halt. A number of CFC alternatives have been discovered, some of them are still under scrutiny for suspected ozone-damaging qualities.
The EPA has proposed the Significant New Alternatives Policy (SNAP) to evaluate substances similar to CFC’s but not ozone-destructive. Over 250 compounds have been approved for industrial and consumer use, and many of these compounds are already available. Applications for these chemicals range from the manufacture of polystyrene to home fire extinguishers.5
One alternative being studied by major U.S. research laboratories are aerogels. Aerogels are sol-gel substances that have the insulation properties of CFC-made foams. Aerogels can be molded into any shape and are stronger than Styrofoam. While aerogels share many properties with plastics, they cannot be shaped as easily. Therefore, until better manufacturing technology can be implemented, aerogels will remain experimental.6
There is no obvious solution to the ozone layer problem. It has been estimated that if CFC production ceased today, people living 70 years from now would still have to deal with their effects. Also, conflicts between industrialists and environmentalists in government have prevented sufficient CFC-blocking legislation from being fully effective. If the ozone layer can be repaired, it will take a massive effort by the people and government to make it successful.
1 Zurer, Pamela. “Record Low Ozone Levels Observed over Arctic.” Chemical and Engineering News 10 Apr. 1995: 8-9.
2 Davies, Owen. “Air Repair.” Omni June 1993: 62+.
3 “Ozone Depletion FAQ.” Online. Internet. Available www.cis.ohio-state.edu/hypertext/ faq/usenet/ozone-depletion/top.html.
4 “Ozone Layer.” Microsoft Encarta 96 Encyclopedia. CD-ROM. Microsoft. 1996
5 Zurer, Pamela. “EPA Lists Acceptable Substitutes for CFCs.” Chemical and Engineering News 3 May. 1993: 9-10.
6 Cook, Brian M. “Insulating the Environment: Will a ‘New’ 61-Year-Old Material Solve the CFC Problem?” Industry Week 6 July 1992: 59.