Greenhouse effect

The energy, which drives our weather and climate, comes from the sun. The Earth receives energy, largely in the form that we see as visible light. The visible light from the sun passes through the atmosphere to warm the earth. In turn the warm earth radiates this energy back toward space as infra-red radiation. On the way some of it is absorbed by gases in the atmosphere. They reradiate some of this energy back toward the earth.

Thus these gases act as an insulating blanket keeping the earth much warmer than it would be without them. If these gases were not present, all of the heat the earth radiates would be lost into space. This is similar to the effect of glass in a greenhouse, which allows the sunlight in but keeps some of the radiated heat from escaping. Hence the gases in the atmosphere, which absorb radiated heat, are called the greenhouse gases, and the process is known as greenhouse effect.

Greenhouse gases occur naturally in the atmosphere. The natural greenhouse effect keeps the temperature of the Earth some 30 ºC warmer than it would be otherwise. Without it the Earth would be too cold to support life, the oceans would freeze. Water vapour is the most important natural greenhouse gas. Its concentration in the atmosphere depends on the Earth′s temperature. The concentration of other natural greenhouse gases is determined by the balance between the processes, which produce them (‘sources’) and those, which absorb them (‘sinks’). The main natural greenhouse gases are: carbon dioxide (CO₂), methane (CH₂), nitrous oxide (N₂O), and ozone (O₃).

3. Make up the plan to the text.

4. Give a brief summary of the text.

Text D

1. Read the text and choose the most suitable title out of the given ones:

a) Sources and Composition of Atmospheric Pollutants.

b) Purification of Air.

c) Consequences of Air Pollution.

Scientists distinguish between natural and artificial sources of atmospheric pollution.

Natural pollution of the atmosphere occurs when volcanoes erupt, dust storms take place, forest fires occur as a result of lightning, and sea salt is washed ashore. The pollution always contains aeroplankton, fungi spores, plant pollen, etc.

Artificial pollution of the atmosphere is characteristic mostly of cities and industrial districts. Cities and suburbs contain numerous industrial enterprises, automobiles and heating systems which pollute the atmosphere and negatively influence the local climate.

Industry pollutes the atmosphere by emissions of harmful gases and industrial dust. Thermal electric plants, metallurgical and chemical factories, oil refineries, cement and other works are sources of air pollution.

The chemical composition of emissions into the atmosphere is different depending on the kind of fuel, of raw materials, technology, etc. For example, blast furnace gas contains poisonous carbon monoxide, while the smoke of aluminum factories pollutes the atmosphere with fluoride compounds. Paper manufacturing enterprises emit soot, sulphurous anhydride, hydrogen sulfide and mercapton into the air. The making of synthetic fibers is accompanied by the emission of toxic carbon disulfide (CS₂) and hydrogen sulfide.

City air is polluted not only by exhaust fumes but also by the products of their oxidation, often more toxic than the initial substance. One of them is ozone which is useful in small quantities, but is deadly poisonous in large concentrations.

2. Write out:

а) key words and terms;

b) the sentences expressing the main idea of each paragraph.

Unit 7

Дата добавления: 2014-10-17