Chlorofluorocarbons CFCs Essay Research Paper CFCs are

Chlorofluorocarbons (CFCs) Essay, Research Paper

CFCs are a family of man-made gases used for various industrial purposes. First developed in the 1920’s in the United States, CFCs have been used in large quantaties since 1950. The industrialized countries can account for over 80% of CFCs use. CFC-11 is used primarily as a propellant in aerosol cans, although its use has been phased out it is still used in the production of plastic foams. CFC-12 is used in foam production as well as cooling coals of refrigerators and air conditioners. HCFC-22 was recently introduced as a replacement for CFC-12 because of its shorter life in the atmosphere, and thus is less of an ozone depleting drug. CFC-113, methyl chloroform, and carbon tetrachloride are used as solvents for cleaning, carbon tetrachloride is also a feed stock for the production of CFC-11 and CFC-12. CFCs are released in relatively small quantities, but one kilogram of the most common CFCs may have a direct effect on climate 1000 times large than that of one kilogram of carbon. In addition over the last two decades the percentage increase of CFCs in the atmosphere has been higher than any other greenhouse gas. By 1990 the increase was 4-12% a year.CFCs also destroy ozone – itself a greenhouse gas – their net effect on climate is unclear. The strength of the indirect effect of ozone depletion depends on variables such as temperature of the upper atmosphere and cannot yet be measured with any confidence. According to new research, however, it is possible that the indirect effect of CFCs cancels out some or all of the direct effect of their being powerful greenhouse gases.CFCs are generally colorless, odorless, and non-toxic. They also do not react chemically with other materials, and as a result they remain in the atmosphere for a very long time — often 50 to 100 years — before they are destroyed by reactions catalyzed by the sunlight. CFCs are composed of carbon, chlorine, and fluorine. Together with other manufactured gases that contain either fluorine or chlorine, and with bromine-containg Halons, CFC’s are referred to collectively as halogenated compounds, or halocarbons. There is an often significant lag time between the production of CFCs and their escape into the atmosphere. Some CFCs, such as those used in spray cans or as solvents for washing electronic parts, are emitted within just a few months or years of being produced. Others, such as that contained in durable equipment such as air conditioners, refrigerators, and fire extinguishers, may not be released for decades. Even if the use of CFCs were stopped it would take decades for the level of CFCs to fall to 0, unless some methods were adopted to capture and recycle CFCs. Although they are important greenhouse gases CFCs are better known for their role in damaging the ozone layer. CFCs first came to the publics attention in the mid-1980’s when a hole was discovered in the ozone layer over Antarctica. Scientist known that the complex series chemical reactions only occur during the Arctic and Antarctic spring times. The Stratosphere ozone forms a protective layer that blocks out the sun’s ultraviolet (UV) rays that cause skin cancer and other cell damage. In response to this weakening shield, most of the world’s CFC users adopted the “Montreal Protocol” in 1987. This treaty commits nations who signed it to phase out CFC use by the year 2000. In November of 1992, growing fears of the ozone depletion lead to the Copenhagen agreement, which commits governments to phase out the most destructive CFCs by 1996. Alternatives are being developed to replace CFCs. Some of these substitutes are halocarbons, such as the compound HCFC-22, which can replace CFC-12 in refrigeration and air-conditioning. These substitutes are also greenhouse gases, but because they are shorter-lived than the CFCs used now they will have a more limited long-term effect on the atmosphere. Other substitutes that are less harmful than CFC-22 have been developed and tested and are now being rapidly introduced for various applications. Additional solutions involve change in the industries to eliminate the need for halocarbons althogeter.For example water based cleaners are increasingly being sold for CFCs in the electronic industries, and non-pressurized, or pump spray bottles are being sold instead of CFC-driven spray cans.


Все материалы в разделе "Иностранный язык"

ДОБАВИТЬ КОММЕНТАРИЙ  [можно без регистрации]
перед публикацией все комментарии рассматриваются модератором сайта - спам опубликован не будет

Ваше имя:


Хотите опубликовать свою статью или создать цикл из статей и лекций?
Это очень просто – нужна только регистрация на сайте.

Copyright © 2015-2018. All rigths reserved.