POLLUTANTS.

Scientists distinguish between natural and. artificial sources of atmospheric pollution.

Natural pollution of the atmosphere occurs when volcanoes erupt, rock is weathered, dust storms take place, forests fire and sea salt is washed ashore. The atmosphere always contains aeroplankton (bacteria, including those causing disease), 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 system which pollute the atmosphere and negatively influence the local climate. It has been established that air pollution in urban areas grows in proportion to the population. 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.

For a long, fine the problem of air pollution in the cities was chiefly connected with coal-burning in heating system which emitted smoke, ashes and sulphurous gas (SO₂). Large amounts of dust are emitted into the atmosphere by thermal electric plants using low-grade coals that yield large quantities of soot and a high percentage of sulphur-containing compounds. Most electric power plants which burn 2000 tons of low-grade coal a day emit about 400 tons of sulphurous gas every day.

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

Today automobiles are the primary sources of atmospheric pollution. The number of automobiles is rapidly increasing in all industrial countries. There are more than 400 million motor vehicles in the world today. It is estimated that one car burns up the amount of fresh air needed for 100 adults to breathe. At the same time it emits the same amount of fumes into the atmosphere. It was stated that automobile exhaust gases are a complicated mixture of many components. But their diversity may be broken down into several groups.

The first group includes non-toxic substances: nitrogen, oxygen, hydrogen and water vapour. Carbon dioxide (C0₂) may also be included in this group as it is not a threat to man.

The second group includes carbon monoxide (CO), a very toxic gas introduced in large quantities (up to 12 per cent).

The third group consists of the nitrogen monoxide (NO) and dioxide (NO2), also very toxic.

The fourth, the most numerous group of substances consists of the carbohydrates, including ethylene, acetylene, methane, propane, toluene, and others.

The fifth group is made up of the aldehydes, mostly the very toxic formaldehyde (formalin).

Finally, the sixth group is soot emitted by Diesel engines. It has the capacity to adsorb the carcinogenic substances contained in exhaust fumes.

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

6. Generalize each group of the words by one term or notion:

1) bacteria, fungi spores, microbes;

2) formaldehyde, nitrogen monoxide, carbon disulfide;

3) chemical factories, oil refineries, automobiles;

4) exhaust fumes, smoke, harmful gases, industrial dust;

5) methane, propane, toluene.

7. Answer the questions:

1. What are the sources of industrial pollution in the city you live?

2. What kind of natural pollution is the most common in this area? Is it seasonal? Does it take place all year round?

3. What streets/districts are affected by exhaust fumes most of all?

4. Are the thermal electric plants situated beyond city limits? Are they the sources of sulphurous gas?

8. a) Read, understand and title the text./give a suitable title to the text.