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| THE HOLE IN THE OZONE LAYER |
| Discovery of the hole in the ozone layer showed that human activity has a major impact on the Earth. The damage of ozone in the stratosphere high above the planet's surface has been brought about as the result of the widespread use of chemicals, which under normal conditions are chemically inert and harmless. Ozone occurs at all levels in the atmosphere, but most of it is found in the stratosphere, between about 15-50 kilometers above the Earth's surface, where it plays a very important role. Ozone absorbs harmful ultraviolet radiation which is produced by the Sun. Ultraviolet radiation can damage cells of living things — plants, animals and people. Whereas small doses result in nothing worse than sunburn, larger amounts may cause cataracts or skin cancer, and can affect the growth of plants.The damage of ozone has been caused by complex chemical reactions involving chlorine and bromine. Large amounts of gas called CFCs were produced in twentieth century for use in everyday appliances like fridges, aerosol spray cans, and fire extinguishers. At ground level, these compounds are chemically non-reactive. However they are carried on wind systems up into the high atmosphere, where the ozone layer is. CFCs can be broken up by the intense sunlight, but before their destruction CFCs gases become reactive and damage the ozone layer.The hole in the ozone layer is formed over the Antarctic continent each spring. During the long dark Antarctic winter, the atmosphere becomes colder than anywhere else on the Earth. Strong winds enclose the cold air above the Antarctic, allowing ice clouds to form. The ice crystals provide the sites where chlorine reacts with ozone when sunlight returns in the spring, and results in the ozone hole. In early summer, the ozone hole mixes with the rest of the air mass of the stratosphere. Over the past years, the concentrations of chlorine in the atmosphere have been steadily increasing, and as a result — more ozone has been destroyed.Ozone itself is a useful protective layer high above our heads, but in the cities is pollutant agent. The CFCs have other effects too. As well as contributing to the breakdown of ozone, CFCs are also very effective in providing «greenhouse effect», contributing to a gradual warming of the atmosphere. However, the possible change in climate resulting from increases in various greenhouse gases might actually make the stratosphere colder, not warmer.Governments of many countries agreed in 1987 to the Montreal Protocol in an effort to reduce the amount of CFCs, and so protect the ozone layer. Since then, more countries have signed it, and more substances included for control. As a result, the amount of chlorine and bromine in the atmosphere is decreasing. With less chlorine in the atmosphere the ozone hole should become smaller, and eventually close up, but it might take 20-30 years. |
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