Sources and composition of atmospheric pollutants

Scientists distinguish between natural and artificial sources of atmospheric pollution.

Natural pollution of the atmosphere occur when volcanoes erupt, rock is weathered, dust storms take place, forest fires occur as a result of lightning, 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.

For a long time the problem of air pollution in the cities was chiefly connected with coal-burning in heating system which emitted smoke, ashes and sulphurous gas (SO). Today industrial enterprises and automobiles are the primary sources of atmospheric pollution.

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 the atmosphere is different depending onthe 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 mercaptan into the air. The making of synthetic fibers (nylon, for example) is accompanied by the emmition of toxic carbon disulfide (CS) and hydrogen sulfide.

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 sulfer-containing compounds. Most electric power plants which burn 2,000 tons of low-grade coal a day emit about 400 tons of sulphurous gas every day.

The number of automobiles is rapidly increasing in all industrial countries. There are more than 300 million motor vehicles in the world today. The automobile is a convenient means of transport, but it has a negative influence on the environment. 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.

Research carried out in the country has shown 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 (CO) 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 and present inlarge quantities (up to 12 per cent).

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

The fourth, 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).

Finely, 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 more toxic than the initial substance. One of them is ozone which useful in small quantities, but is deadly poisonous in large concentrations.

The problem of radioactive pollution of the atmosphere arose in 1945 after the atomic bombs were dropped on the Japanese cities of Hiroshima and Nagasaki. Since then atomic weapons have become much more powerful and have been stockpiled in large quantities.

When an atom bomb explodes, an extremely high level of radiation covers an enormous area for a long period of time as the radioactive particles are dispersed. From the atmosphere, the radioactive products fall on the earth, polluting the soil, water bodies and living organisms. Finely dispersed dust is carried many thousand of kilometres away and cause global radioactive pollution of the atmosphere.

Radioactive elements (isotopes) formed during the explosion are taken in the human body in different ways and have different effect.

Ex.6 Complete the following sentences using the text:

1.It has been established that air pollution in urban areas grows in....2. The chemical composition of emissions into the atmosphere is different depending on....3. Large amounts of dust are emitted into the atmosphere by.... 4. The automobile is a covenient means of transport, but it has.... 5. City air is polluted not only by exhaust fumes but also by.... 6. The problem of radioactive pollution of the atmosphere arose in1945 after....7.Radioactive elements formed during the explosion are taken in by....

Date: 2015-09-02; view: 789; Нарушение авторских прав