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Air pollution as an important hygienic and environmental problem. Self-cleaning of air and its sanitary protection



The composition of the air environment constantly includes a variety of extraneous impurities falling into it from various sources. Over time, as a result of human activities aimed at the development of technological progress, the number of such impurities to the air increases. Currently, the so-called clean air in populated areas can practically be shown only in the form of an exhibit.

All air pollution can be divided into three types:

1. Solid (dust).

2. Liquid (vapors).

3. Gaseous.

Solid pollution (dust) by origin can be divided into several categories:

a) soil dust. Rises in the air of the soil surface as a result of the movement of air masses. This is especially facilitated by the movement of vehicles.

b) Cosmic dust. A certain amount of solid particles that are not of practical importance are deposited on earth from space.

c) Sea dust. It is formed as a result of drying of salt water splashes during sea waves. Also has no practical value.

d) Solid emissions into the atmosphere from power plants (industrial enterprises and heating systems).

e) Sometimes a separate category is allocated radioactive dust that enters the air as a result of emergency situations at enterprises using radionuclides.

Of the greatest practical importance are dust pollution emitted into the air by energy systems, since the number of the latter is constantly increasing. Moreover, the role of industrial enterprises and home heating systems may vary depending on local conditions. In some places, industrial enterprises play a leading role; in others, home heating systems. But in general, industrial enterprises are leading in this regard. According to data obtained from many countries, it is noted that with the development of industry, the amount of pollution entering the air increases proportionally. Especially a lot of solid pollution enters the air when burning solid fuel (coal). At the same time, 1) ash, 2) underburning, 3) soot are thrown into the air.

Ash is a non-combustible impurity to coal, the content of which in it can vary from 6-12% (high-grade coals) to 30-35% (low-grade).

The burn is unburned coal particles, the amount of which depends on the degree of aeration of the power plant.

Soot is a product of incomplete combustion of coal. It is the most pathogenic component of solid emissions, as it contains tarry substances, among which there are carcinogenic resins (3,4-benzpyrene, 1,2,5,6-dibenzanthracene, methyl-cholanthrene, etc.).

Ash is the most significant component of emissions from power plants.

There are two ways to burn coal: layered and pulverized. In the first method, coal is poured into the furnace in layers; in the second, it is preliminarily crushed and introduced into the furnace in the form of dust. In this case, the efficiency increases significantly.

During the pulverized combustion of fuel, which is the most efficient, about 80% of the ash is thrown into the air (through a pipe). Therefore, when burning coal containing 30% ash (for example, coal near Moscow), about 240 kg of ash for each ton of fuel burned into the air (300 tons of ash are contained in one ton, 80% of which will be 240 kg). Thus, a large CHP plant, consuming about 1000 tons of coal per day, emits about 240 tons of ash. For clarity, you can imagine that these are 80 three-ton trucks. To this should be added another burn and soot. In addition, some industrial enterprises emit specific products that pollute the atmosphere (for example, cement plants) into the air. As a result, a huge amount of dust is floating in the air in cities with developed industry. In particular, it was found that in large cities with developed industry, dust, measured in thousands of tons per year, settles out of the air for every square kilometer of the surface. For example, in Lugansk - about 1300 t / km, in Dnepropetrovsk - about t / km, etc., and this data clearly shows the influence of industrial development on the degree of air pollution. For example, in Ostrava in 1954, 557 tons of dust settled on every kilometer of the surface, and 1958, with the development of industry - 1018 tons. The same examples can be given in other cities.

Atmospheric dust in accordance with the Gibbs classification is divided into the following categories:

a) the dust itself (settles with acceleration, particle size 100-10 microns);

b) clouds or mists (settles at a constant speed, particle size 10-0.1 microns);

c) smoke (does not settle, but is constantly in a state of Brownian motion, the particle size is less than 0.1 microns).

The degree of dispersion of dust particles is also important in terms of their penetration into the respiratory tract. The largest dust (particle size greater than 10 microns) is mainly retained in the upper respiratory tract and is excreted with the secretion of the mucous membranes. Dust with a particle size of 5 to 10 microns penetrates more deeply.
The most dangerous is dust with a particle size of less than 5 microns, which penetrates the alveoli.

Sources of gaseous air pollution are mainly industrial enterprises and heating systems in which coal is burned, however, vehicles using internal combustion engines should also be mentioned as sources of gaseous pollution. Coal contains sulfur as a constant impurity, which, when coal is burned, oxidizes to sulfur dioxide. This gas is the main component of gaseous pollutants emitted into the air by power plants.

In addition to dust, each large CHP plant emits about 300 tons of sulfur dioxide per day, as well as carbon monoxide, carbon dioxide, nitrogen oxides, etc. In addition, many industrial enterprises emit a significant amount of specific gaseous impurities into the air. In particular, chemical plants emit a huge amount of various toxic components into the air.

Road transport, widespread in modern cities, is the main source of air pollution with carbon monoxide. In addition, transport emits a variety of nitrogen oxides, carbon dioxide, underburned hydrocarbons, ozone and other gases into the air. Diesel engines also emit soot into the air, and engines that use leaded gasoline as fuel produce significant amounts of lead. Each working car engine usually emits about 3 m of pure carbon monoxide per hour into the air, and the freight - twice as much. The number of motor vehicles is constantly growing, and currently the number of cars in the world is comparable to the number of people.

As a result of this, the concentration of carbon monoxide in the air of large cities with heavy automobile traffic significantly exceeds the maximum permissible norms.

Liquid pollution is formed in the air mainly due to the interaction of gaseous pollution with atmospheric moisture. As a result, for example, from sulfur dioxide emitted into the air by energy systems, acids containing sulfur, etc., are formed, which then fall out of the atmosphere in the form of so-called acid rains.

Currently, all the air pollution taken together reach in many cases such high concentrations that pose a danger to human health and life. High degrees of air pollution are now called toxic fogs or smogs. Such smogs in the past were quite rare, and only in some cities that differ in characteristic weather conditions. The fact is that weather conditions play a significant role in the occurrence of such toxic mists. The latter are usually formed with some combination of meteorological factors: with low cloud cover, the presence of temperature inversion (see the previous lecture), and calm. It is with such a combination of meteorological conditions that the pollutants emitted into the air are not carried by the wind, that is, they are not diluted and concentrated at the surface of the earth. Previously, the classic city where these fogs appeared was London, but in recent years the geography of their occurrence has expanded dramatically. They began to appear in almost all cities of the world, even in Japan, where the smog was called "kogai". In this regard, many cities are forced to take emergency measures to protect people from the harmful effects of these smogs. For example, in Los Angeles, when certain concentrations of toxic substances are reached in the air, alarms 1, 2, 3 are announced. In accordance with the announcement of these alarms, measures are taken to reduce the concentration of these pollutants: some enterprises that release especially large amounts of toxic substances are suspended Some traffic routes overlap for traffic. It is known, for example, that the Turkish authorities, upon reaching high concentrations of air pollution, stop the activities of some schools, do not recommend people to go out, etc. This is especially true for children and the elderly. In Germany and Japan, under such circumstances, people are advised to use respiratory protection devices (respirators, gas masks).

The degree of air pollution largely depends on a variety of conditions:

a) from the time of year (more in winter than in summer, because heating systems are turned on);

b) the time of day (maximum - in the morning, minimum - at night);

c) on the strength and direction of the wind (dilution); d) from a vertical temperature gradient (temperature inversion);

e) on the degree of air humidity (mists contribute to the concentration of pollution);

e) the frequency and amount of precipitation;

g) from the distance with respect to the sources of emissions.

The greatest amount of dust settles near the place of emission. So, around a thermal power plant with an emission amount of 200 tons / day, the dust concentration reaches: at a distance of 0.5 km - 5.94 mg / m at a distance of 1 km - 3.11 mg / m at a distance of 2 km - 1.21 mg / m at a distance of 3 km - 0.47 mg / m

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