Depletion of the ozone layer

1. Ozone, the triatomic form of oxygen (O₃), is primarily concentrated in a layer high above the earth within the stratosphere. While the actual amount of ozone in the atmosphere is small, its ability to absorb harmful ultraviolet rays from the sun makes it vital to humans.

2. In 1974 scientists first documented that man-made gases can interact with ozone and convert it to diatomic oxygen (O₂), which offers no protection from ultraviolet radiation. While several gases have been linked to this ozone depletion process, the primary culprit seems to be chlorofluorocarbons (CFCs) which are gases involved in the green­house effect as well. CFCs are used in refrigeration, air conditioning, insulation, packing materials (fast food containers), and as propellant for aerosol cans.

3. These chemicals have already upset the state of equilibrium that has existed in the ozone concentration for millions of years. The hole in the ozone layer over Antarctica (which can be seen due to the unusual weather conditions of this region) has been growing larger each year. Scientists believe that variations in that region could serve as a gauge of depletion of the ozone layer in other regions of the world. This relationship appears to be true. A recent study (1991) found that the ozone layer over the midlatitudes has been depleted 2 to 3 percent since 1979.

4. The Environmental Protection Agency estimates that every 1-percent decrease in stratospheric ozone could result in 24,000 to 57,000 more cases of cataracts and 43,000 new cases of skin cancer each year in the United States. Increased ultraviolet radiation would also increase the effects of many diseases that affect the skin or start on the skin. Excessive ultraviolet radiation causes cell and tissue damage in many plants. This could result in a significant reduction in crop yields throughout the world.

5. What can be done? In 1987, 38 countries met in Montreal to sign an agreement — the so-called Montreal Protocol — to cut CFCs use in half by the end of the century. This historic first effort towards international control of an air pollutant is hopefully only the beginning.

II Прочтите 2-ой абзац текста и письменно ответьте на следующий вопрос:

What gases are considered to be the primary culprit in the ozone depletion process?

Дата добавления: 2015-07-11