Реферат: Ozone Essay Research Paper Ozone pronounced OH
Ozone Essay, Research Paper
Ozone, pronounced OH Zohn, is a form of oxygen that is present in the earth’s atmosphere in small amounts. Ozone in the upper atmosphere is a major factor in making life on earth possible. But ozone in the lower atmosphere contributes to air pollution. Ozone is used commercially in water purification process and as a bleaching agent.
Ordinary oxygen molecules have two oxygen atoms, ozone has three. Ozone is produced naturally through photochemical and electric discharge reactions. Photochemical production occurs when high energy radiation from the sun strikes ordinary oxygen in the earth’s upper atmosphere and converts some of it to ozone. Electric discharge reactions, including lightening and electric sparks from motors, also convert some oxygen to ozone. Ozone is produced commercially by electric discharges in a machine called an ozonizer.
Ozone has a molecular weight of 47,998, pure ozone is a pale blue gas. It was first detected by means of its sharp, irritating odor, which is often noticed near electrical switches and machinery. The german chemist christian Friedrich Schonbein discovered ozone in 1840.
Ozone in the upper atmosphere has the highest concentration reached depending on the latitude, between 9 and 18 miles ( 15 and 30 kilometers ) above the earth’s surface. This concentration is 10 parts per million by volume, that is 10 parts ozone per 1 million parts air. This ozone layer in the upper atmosphere shields the earth from 95 to 99 per cent of the sun’s ultraviolet rays. Overexposure to these rays is a cause of skin cancer.
Most ozone in the lower atmosphere is considered an air pollutants. It is formed by chemical reactions between sunlight and pollutants already in the atmosphere. Ozone produced in this manner is a component of photochemical smog. Such ozone can directly damage rubber, plastic, and plant and animal tissue. It may undergo further chemical reactions that produce other damaging chemicals. Exposure to certain concentrations causes headaches, burning eyes, and irritation of the respiratory tract in many individuals
In the mid 1970’s, some scientist expressed concern that chemical compounds called chlorofluorocarbons ( cfc’s ) were breaking down the protective layer of ozone. At that time, CFC’s were widely used as propellants in aerosol spray cans. After CFC’s are released, they slowly rise into the atmosphere. When they reach the upper atmosphere, the sun’s ultraviolet radiation breaks them apart. Some of the molecular fragments that result react with ozone, thereby reducing the amount of it.
Since the 1970’s, scientist have observed that the ozone layer over antarctica thins dramatically every year in the spring. As much as 50 per cent of the molecules may disappear, creating what is called an ozone hole. Scientist believe that antarctica’s unusual weather conditions increase the reactions between CFC’s and ozone. These conditions include extreme cold, swirling wind patterns, and complete darkness during the winter. When sunlight first appears in the spring, it triggers the chemical reations that destroyed the ozone.
Scientist have also discovered that a much less severe ozone hole occurs over the arctic in late winter. Some experts fear that the ozone layer may eventually thin over more populated areas, endangering human health and harming many plants and animals. Scientist measure changes in ozone in the upper atmosphere with instruments on aircraft, balloons, and satellites.
In 1978, the united states government banned fluorocarbon aerosols for most uses. However, the ban did not affect the use of CFC’s as refrigerants or in insulation. In 1990, the united states and 55 other nations agreed to end the production of CFC’s by the year 2000.