Carbon monoxide(CO, carbon monoxide) is a product of incomplete combustion of fuel that enters the atmospheric air with emissions from industrial enterprises and vehicle exhaust gases. Carbon monoxide can appear in the air of residential premises during stove heating in case of premature closing of the chimney, in gasified premises due to faulty burners and as a result of gas leakage from the network. Tobacco smoke contains about 0.5-1.0% carbon monoxide. In industrial environments, carbon monoxide can form and accumulate in work areas as a result of technological processes. It is generally accepted that 1/3 of the total amount of CO polluting the atmosphere is associated with human activity.

Carbon monoxide is a toxic substance. Penetrating through the lungs into the blood, it forms a strong chemical compound with hemoglobin - carboxyhemoglobin, blocking the processes of oxygen transport to tissues, as a result of which oxygen starvation occurs in the body - anoxemia of an acute or chronic nature, depending on the concentration of CO. Chronic poisoning is more common, manifested by headache, memory loss, sleep disturbance, increased fatigue, etc.

Methane(CH 4 ) - It is formed both naturally as a result of the vital activity of microorganisms in stagnant and soil waters, and as a result of human activity: during the development and operation of gas and oil fields, the use of natural gas, and the combustion of coal. In recent years, the amount of methane in the atmosphere has increased by 1% per year.

Sulfur dioxide(SO 2, sulfur dioxide) – refers to priority pollutants. It is released into the atmosphere when fuels rich in sulfur are burned, such as coal and sulfur-rich oils at thermal power plants, oil refineries, boiler houses and other industrial enterprises.

Sulfur dioxide has a pungent odor and irritates the mucous membranes of the eyes and upper respiratory tract. In case of chronic poisoning, conjunctivitis, bronchitis and other lesions are observed. This gas has a harmful effect on vegetation, especially coniferous trees, as well as on metal surfaces, causing their corrosion, as sulfur dioxide is oxidized into sulfur trioxide, which, with air moisture, forms an aerosol of sulfuric acid, which is part of acid rain.

Nitrogen oxides ( NO, NO2, N2O) - are found in vehicle exhaust gases and in emissions from industrial enterprises producing nitric acid, nitrogen fertilizers, explosives, etc. The most harmful substance is nitrogen dioxide (NO 2), which has an irritating effect on the mucous membranes of the upper respiratory tract. Once in the human body, it interacts with hemoglobin in the blood, causing the formation methemoglobin and hypoxic disorders. Long-term inhalation of low concentrations of nitrogen oxides causes bronchitis, anemia, and worsening heart disease.

The decomposition of nitrogen dioxide in atmospheric air under the influence of ultraviolet rays on nitrogen oxide and atomic oxygen leads to the formation of ozone free radicals. Nitrogen oxides and hydrocarbons combine with oxygen and form oxidants, among which there are very toxic substances involved in the formation of photochemical smog along with nitrogen oxides.

Carcinogenic hydrocarbons- these are polycyclic aromatic hydrocarbons, the strongest of which is 3-4-benzo(a)pyrene, which enter the atmosphere with the exhaust gases of internal combustion engines, emissions from oil and coke industry enterprises and other enterprises using oil and coal as fuel . 3-4-benz(a)pyrene is also found in tobacco smoke.

The relationship between the level of atmospheric air pollution with carcinogens and the incidence of lung cancer has long been established.

Other harmful impurities. Particulate matter suspended in the atmospheric air consists of dust of natural and artificial origin. The following types of natural dust are distinguished: cosmic, volcanic, marine, forest fires and terrestrial, which has the greatest hygienic value. It consists of soil dust and plant dust. Soil dust from populated areas located in desert and semi-desert areas consists of 70-80% mineral compounds with a high content of free silicon dioxide, but the risk of silicosis from it is low.

Plant dust includes pollen from flowering plants, fungal and bacterial spores.

Dust of artificial origin enters the air during combustion solid fuel(coal) in the form of ash, underburning and soot. Ash is a non-combustible impurity to coal, underburning is unburned coal particles, soot is a product of incomplete combustion of coal, which is the most pathogenic component, as it contains carcinogenic substances [benzo(a)pyrene, methylcholanthrene, anthracene].

Dust can have indirect and direct adverse effects on humans. The indirect effect of dust is noted in the atmosphere and consists in reducing the intensity of solar radiation, promoting the formation of clouds and fogs, which leads to a decrease in natural illumination of rooms and, as a result, myopia and rickets in children, osteoporosis in adults, promotes the survival of pathogenic microbes in environment. The direct effect of dust: irritating, mechanical, carcinogenic, toxic, epidemiological, fibrogenic, cariogenic, radiation, allergenic, epidemiological - can be observed in unfavorable production conditions.

Chlorine and fluorine compounds(CH 3 C1, HC1, freons and products of their destruction). Under natural conditions, methyl chloride (CH 3 C1) is formed in ocean water, which rises into the stratosphere and, under the influence of solar radiation, decomposes into chlorine atoms. Hydrochloric acid is then formed from chlorine. However, natural chlorine and its compounds have little impact on the atmosphere. A great danger is posed by anthropogenic pollution of the atmosphere with chemical compounds containing chlorine or fluorine, or both of these elements. These are the so-called freons: chlorofluoro derivatives of methane, ethane and cyclobutane (CFC1 ​​3, CF 2 C1 2, etc.).

Freons are widely used as solvents in aerosol cans for various purposes, as coolants in refrigerators and air conditioners. Freons easily penetrate into the stratosphere, as they are inert gases. However, at altitudes of 30 - 40 km, under the influence of the ultraviolet part of solar radiation (in the wavelength range 180 - 225 nm), they decompose with the release of active chlorine atoms. Then, when interacting with oxygen, chlorine oxide (C1 2 0) is formed, and in reactions with HN0 3, CH 4 and other chemical compounds, hydrogen chloride (HCl) is formed. Hydrogen chloride is highly soluble in water, so it is effectively washed out by sediment.

A significant amount of hydrogen chloride (from hundreds of thousands to 1.5 million tons) is released into the stratosphere (up to an altitude of 18 - 20 km) after large volcanic eruptions. On average, over 1 year, about 0.3 million tons of HC1 enter the stratosphere due to volcanic activity.

In 1987, in accordance with the United Nations Environment Program (UNEP), the Montreal Protocol on Substances that Deplete the Ozone Layer came into force, providing for a gradual reduction in the production and consumption of a number of chlorofluorocarbons. In particular, in accordance with this protocol, freon R-12 (as the most conducive to the destruction of the ozone layer) and R-22, as well as other freons that destroy
ozone layer, are no longer used in household appliances.

The permanent impurities of steels are considered to be manganese, silicon, phosphorus, sulfur, as well as gases (hydrogen, nitrogen, oxygen), which are constantly present in varying quantities in technical grades of steel.

With a higher content of them, the steel should be classified as alloyed when these elements are introduced specifically (hence the name alloy steel or special steel).

Let us consider the influence of impurities separately.

Manganese. This element is introduced into any steel for deoxidation.

i.e., to eliminate harmful impurities of ferrous oxide. Manganese also eliminates harmful iron sulfur compounds (see below) and dissolves in ferrite and cementite.

Manganese significantly affects the properties of steel, increasing the strength in hot-rolled products and changing some other properties. But since the manganese content in all steels is approximately the same, its effect on steel of different composition remains unnoticeable.

Silicon. The effect of initial silicon additives is similar to the effect of manganese. Silicon deoxidizes steel according to the reaction:

Silicon is not structurally detectable, since it is completely soluble in ferrite, except for that part of the silicon that, in the form of silicon oxide, did not have time to float into the slag and remained in the metal in the form of silicate inclusions.

Phosphorus. Iron ores, as well as fuels and fluxes, contain some amount of phosphorus, which during the production of cast iron remains in it to varying degrees and is then converted into steel.

When steel is smelted in basic open-hearth furnaces, most of the phosphorus is removed from the metal. Steel smelted in the main

open hearth furnace contains a little phosphorus (0.02-0.04%), and in an electric furnace it contains less than 0.02%. It is difficult to reduce the content to 0.01% or less by metallurgical methods and this is achieved by using the original high-purity charge (for example, PV iron). The iron-phosphorus phase diagram is shown in Fig. 150, a.

The solubility of phosphorus at high temperatures reaches 1.2%, but it decreases sharply with decreasing temperature (Fig. 150, b) and, according to recent studies, at 200 ° C and below it is only However, this amount of phosphorus is usually present in steel.

Rice. 160. State diagram: a - general view; b - solubility of P in a-gedez

From this we can conclude that phosphorus is completely dissolved in a-iron.

However, carbon and alloying elements reduce the solubility of phosphorus, however, metallographically excess compounds are not detected. Therefore, in these cases, phosphorus is in an a-solution, but such a solution is supersaturated.

Modern research methods have shown that phosphorus in solution is unevenly distributed and enriches (segregates) grain boundaries. The low rate of diffusion of phosphorus in -iron practically eliminates the release of phosphide precipitates from the solution.

Phosphide inclusions in the form of so-called phosphide eutectic (steadite) are observed in phosphorous cast irons containing phosphorus

Dissolving in -iron, phosphorus sharply increases the temperature of transition to a brittle state (Fig. 151), otherwise it causes cold brittleness in steel. Thus, phosphorus is a harmful element. It should be noted that in some cases phosphorus is desirable

element, since, by creating brittleness, it facilitates the machinability of steel with a cutting element, and in the presence of copper, it increases corrosion resistance.

Sulfur. Like phosphorus, sulfur enters the metal from ores, as well as from furnace gases - a product of fuel combustion. In the main open-hearth process and during steel smelting in the main electric furnace, sulfur is removed from the steel.

By treating liquid metal with synthetic slags, the sulfur content can be reduced to 0.005%.

Rice. 151. The influence of phosphorus on the cold brittleness of steel

Rice. 152. State diagram

Sulfur is insoluble in iron (Fig. 152) and any amount of it forms a sulfur compound with iron - iron sulfide, which is part of the eutectic formed when

The presence of a low-melting and brittle eutectic, located, as a rule, along the grain boundaries, makes steel brittle at and above, i.e., in the region of red heat temperatures. This phenomenon is called red brittleness.

Usually, sulfur eutectic, present in small quantities, coalesces, i.e., the ferrite of the eutectic combines with the ferrite of the bulk of the metal, and the compound is located around the grains (Fig. 153, a).

This form of sulfur inclusions is especially harmful, since hot pressure treatment results in tears and cracks.

The latter is related to this. that in the process of heating the steel around the rims of iron sulfide, starting from the temperature, melting occurs (i.e., the formation of a melt in accordance with the diagram shown in Fig. 152). Individual isolated round inclusions of sulfides are already less harmful (Fig. 153, b).

The introduction of manganese into steel reduces the harmful effects of sulfur, since when it is introduced into liquid steel, the formation reaction of manganese sulfide occurs:

Rice. 153. Sulfur inclusions in the form of: a - rim along the grain boundaries; b - isolated inclusions, c - manganese sulfide,

Manganese sulfide melts at, i.e., temperatures significantly higher than the hot working temperature 1.

At hot processing temperatures, manganese sulfide is plastic and, under the influence of external forces, is stretched into oblong lenses (Fig. 153, c; 154, a).

Sulfides are plastic and deform during hot treatment, unlike oxides, which are brittle when exposed to

mechanical forces crumble and are arranged in the form of chains (Fig. 154, b).

The lamellar shape of manganese sulfide inclusions does not affect the properties of steel in the direction along the rolling, but significantly, approximately 2 times, reduces the plastic and viscous properties across the rolling, i.e., it increases the anisotropy of the properties (the ratio of “transverse” and “longitudinal” properties).

A modern method of rounding out sulfide inclusions is the treatment (“modification”) of liquid steel with either silicocalcium or rare earths (cerium).

Rice. 154. Non-metallic inclusions: a - sulfides (plastic); b - oxides (brittle)

These modifiers primarily combine with sulfur, forming calcium sulfides or cerium sulfides, respectively, which at rolling temperatures are stronger than manganese sulfides and do not deform into plates, but retain a rounded shape (see Fig. 153, b), more or less distributed in the metal matrix, without forming chains, unlike oxides.

This modification of sulfide inclusions improves the “transverse” properties and the anisotropy coefficient of relative contraction and impact strength from 0.5 with the lamellar form of sulfides increases to 0.8.

The phenomenon of anisotropy is taken into account in GOST standards and technical conditions for metal products, which stipulate the direction of cutting the sample.

Currently, a widespread method of steel smelting is in which the slag is prepared in a separate furnace (the so-called synthetic slag). As a result of processing the metal with such slag, sulfur is more completely removed, and the properties are also improved, mainly when tested across the fiber.

The effect of sulfur on ductile properties is peculiar, since sulfur is present in most steel grades in the form of manganese sulfides,

this influence is called the sulfide effect. Unlike other “harmful” elements, sulfur does not increase, but even lowers the threshold of cold brittleness, although it reduces the impact strength during ductile fracture (Fig. 155).

In other words, reducing the sulfur content is beneficial in the sense that it increases the resistance to ductile fracture, but reduces the resistance to brittle fracture.

Rice. 155. The influence of sulfur on the tough properties of steel

Like phosphorus, sulfur (see point 6 below) facilitates machinability.

"Gases." Hydrogen, nitrogen and oxygen are contained in steel in small quantities, depending on the production method (Table 15).

Hydrogen, nitrogen, oxygen can be present in the following forms: be in various discontinuities (gaseous state), be in a solid solution; form various

Table 15. (see scan) Approximate gas content in steel, (by weight)

compounds, so-called non-metallic inclusions (nitrides, oxides).

If there is a lot of hydrogen in the metal, this can lead to extremely dangerous internal tears in the metal (flocks, see p. 354).

Brittle non-metallic inclusions formed by nitrogen and oxygen worsen the properties of the metal.

The solubility of hydrogen, nitrogen, oxygen and carbon in a-iron is small, but since this solubility sharply decreases with decreasing temperature (Fig. 156), then under conditions of ordinary (non-equilibrium) cooling of steel after rolling or forging, a supersaturated solid solution of these elements is formed in -iron.

Rice. 156. Solubility of interstitial impurities of carbon, oxygen and nitrogen in a-jelly

Theoretically, it is more correct to call these elements, as well as carbon, interstitial impurities, especially since their effect on properties is specific and similar.

Plastic deformation and subsequent low heating of such a supersaturated solution lead to severe embrittlement due to aging processes (so-called “strain aging”). This is manifested primarily in a decrease in viscosity reserve and an increase in the cold brittleness threshold. Since the content of these impurities is small (see Table 15), their influence on many other properties is unnoticeable. However, unlike almost all mechanical properties, interstitial impurities strongly affect the viscous properties, reducing impact strength and sharply increasing the cold brittleness threshold (Fig. 157, a, b).

Hydrogen does not form compounds with iron (hydrides), so it can be released from the metal. After smelting, steel contains a certain amount of hydrogen, which gradually decreases over time. The duration of this process can be several days, weeks or months (depending on the thickness of the product). At the same time mechanical properties are improving.

From the above it follows that the presence of hydrogen, nitrogen and oxygen in the metal worsens its properties.

A radical means of reducing these elements and non-metallic inclusions in metal is smelting or casting the metal in a vacuum. Vacuumed metal has higher properties due to high purity of non-metallic inclusions and the absence of (virtually) dissolved hydrogen, nitrogen and oxygen atoms.

Impurities of non-ferrous metals. Melting household and machine-building scrap leads to contamination of steel with impurities of non-ferrous metals (etc.). Usually the content of these elements is small - hundredths and even thousandths of a percent (except for copper, the content of which reaches

Steels always contain impurities, which are divided into four groups. 1. Permanent impurities: silicon, manganese, sulfur, phosphorus.

Manganese and silicon are introduced during the steelmaking process for deoxidation; they are technological impurities.

Manganese content does not exceed 0,5…0,8 %. Manganese increases strength without reducing ductility, and sharply reduces the red brittleness of steel caused by the influence of sulfur. It helps reduce iron sulfide content FeS, since it forms a manganese sulfide compound with sulfur MnS. Manganese sulfide particles are located in the form of separate inclusions, which are deformed and appear elongated along the rolling direction.

Being located near the grains, it increases the temperature of transition to a brittle state, causes cold brittleness, reduces the work of crack propagation, increases the phosphorus content for each 0,01 % increases the threshold of cold brittleness by 20…25 o C.

Phosphorus has a tendency to segregate, so in the center of the ingot, individual areas have a sharply reduced viscosity.

For some steels it is possible to increase the phosphorus content to 0,10…0,15 %, to improve machinability.

S– ductility, weldability and corrosion resistance decrease. P-distorts the crystal lattice.

The sulfur content in steels is 0,025…0,06 %. Sulfur is a harmful impurity that gets into steel from cast iron. When interacting with iron, it forms a chemical compound - sulfur sulfide FeS, which, in turn, forms a low-melting eutectic with iron with a melting point 988 o C. When heated for rolling or forging, the eutectic melts and the bonds between grains are broken. During deformation, tears and cracks occur at the locations of the eutectic, and the workpiece is destroyed - a phenomenon red brittleness.

Red brittleness – increased brittleness at high temperatures

Sulfur reduces mechanical properties, especially toughness and ductility

(δ and ψ), as well as the endurance limit. It impairs weldability and corrosion resistance.

2. Hidden impurities- gases (nitrogen, oxygen, hydrogen) - enter the steel during smelting.

Nitrogen and oxygen are found in steel in the form of brittle non-metallic inclusions: oxides ( FeO, SiO 2, Al 2 O 3)nitrides ( Fe2N), in the form of a solid solution or in a free state, located in defects (cavities, cracks).

Interstitial impurities (nitrogen N, oxygen ABOUT) increase the threshold of cold brittleness and reduce the resistance to brittle fracture. Non-metallic inclusions (oxides, nitrides), being stress concentrators, can significantly reduce the endurance limit and viscosity.

Hydrogen dissolved in steel is very harmful, as it significantly embrittles the steel. It leads to the formation of floken.

Floken– thin cracks of an oval or round shape, having the appearance of spots in the fracture – silvery flakes.

Metal with flakes cannot be used in industry; during welding, cold cracks form in the deposited and base metal.

If hydrogen is in the surface layer, it is removed as a result of heating at 150…180 , better in a vacuum ~10 -2 ... 10 -3 mm Hg. Art.

Vacuuming is used to remove hidden impurities.

3. Special impurities– are specially introduced into steel to obtain specified properties. Impurities are called alloying elements, and steels are called alloyed steels.

Cold-worked steel

Wire and thin sheets are widely used in the household. These types of products are produced in metallurgy by rolling and cold drawing. As a result of this treatment, the metal is strengthened due to a phenomenon called cold hardening. Due to room temperature, the hardening is not removed. This type of processing is called cold hardening.

Cold hardening of steel strongly depends on the degree of work hardening and on the carbon content (Fig. 7).

Record values ​​of σв were obtained for compression of up to 90% in 1.2% C steel with a wire ∅ of 0.1 mm.

Hardening is an inevitable process of any plastic deformation. Hardening (hardening) is accompanied by an increase in strength and hardness and a significant decrease in ductility.

Therefore, after rolling or cold drawing, sheets, channels, and pipes are cold-worked.

Most often this is a desired change in properties. Sometimes it's undesirable. For example, you can’t do embossing on a cold-worked copper sheet - it will break. It is necessary to remove the hardening by heat treatment (annealing).

Everything said above about the impact of atmospheric pollution on people, wildlife and vegetation can be confirmed by several examples. As is known, some US oil refineries and enterprises use high-sulfur oil as fuel. In one of the states where such factories and enterprises are located, an extensive medical examination of the population was carried out. The results of the examination showed that people who complained of unpleasant odors had various general painful phenomena: headaches, insomnia, suffocation, irritation of the upper respiratory tract. All these phenomena periodically arose in connection with the entry of harmful impurities into the atmosphere. All the described phenomena often led to increased fatigue, decreased performance and functional disorders of the nervous system. When examining the health status of 1322 junior students (Institute of General and Municipal Hygiene USSR Academy of Medical Sciences), living in the area of ​​emissions from a powerful thermal power plant, many practically healthy children had initial fibrotic changes in the lungs, and the children themselves complained of frequent headaches, general weakness, irritation of the mucous membranes of the eyes, fatigue, etc. The population had similar complaints , living in the area of ​​a viscose factory in Belarus, where there was air pollution with carbon disulfide and sulfur dioxide.

The adverse effect of atmospheric pollution on cattle can be judged by the following fact recorded near one of the West German factories: a large herd cattle, which belonged to the population of the factory village, was completely destroyed. In addition, the population of this village noted a sharp decrease in the number of bees, the death individual species wild animals and damage to vegetation even at a distance of 5 km from the plant. An undoubted role in this was played by air pollution with sulfur dioxide and dust containing arsenic, iron oxide, antimony, etc. There are numerous reports of the death of crowns and destruction of foliage on trees near chemical plants. The harmful effects of atmospheric pollution also include the deterioration of the living conditions of the population: due to unpleasant odors, many are deprived of the opportunity to open windows and ventilate the premises, and the exterior decoration of buildings is contaminated with soot and soot. Some industrial emissions have a destructive effect on the metal roofing of residential and public buildings.

Particular attention should be paid to the fact that some carcinogenic products are found in coal tar and dust. These substances condense on ash and soot particles that enter the atmospheric air in the form of flue gases. This should be remembered, since some types of fuel containing carcinogenic compounds produce very large amounts of flue gases when burned incorrectly. Sources of such air pollution in cities can also be asphalt concrete, roofing felt, roofing felt and slate distillation enterprises. Comparative data on the spread of lung cancer among residents of various populated areas have shown that this disease more often affects people who live for a long time in industrial cities, the air basin of which is characterized by the content of large amounts of atmospheric pollution.

Finally, dust and smoke in the air of populated areas reduce the transparency of the atmosphere, causing a decrease in overall illumination and, most importantly, cause a significant weakening of the intensity of the ultraviolet part of solar radiation. Measurements of diffused light illumination in an industrial area of ​​Moscow and at a distance of 8-10 km from the center found that within the city, illumination is 40-50% lower. Compared to the surrounding area, solar radiation intensity is 25-30% lower in Paris, 50% lower in Baltimore, and 67% lower in Berlin.

The atmospheric air of populated areas, especially large industrial cities, can be polluted by industrial emissions. Sources of atmospheric air pollution with gaseous impurities are enterprises of the chemical, coke-chemical, metallurgical industries, production of polymers, organic solvents, power plants, oil production and oil refining industries, etc., as well as home furnaces and urban vehicles.

The atmospheric air of populated areas can be polluted with sulfur dioxide (SO 2), hydrogen sulfide (H 2 S), carbon disulfide (CS 2), carbon monoxide (CO), nitrogen oxides (N 2 O 5), hydrocarbons, chlorine, lead, mercury vapor, phosphorus, manganese, arsenic, etc.

Sulfur dioxide (SO 2). The most common chemical impurity in atmospheric air is sulfur dioxide. The amount of it in flue gases depends on the sulfur content in the fuel. A powerful source of air pollution with sulfur dioxide are boiler houses that burn a lot of coal, non-ferrous metallurgy enterprises, sulfuric acid production, and coke plants.

The concentration of sulfur dioxide in the atmospheric air depends on the source of pollution, distance from it, wind direction, etc. and varies widely, sometimes reaching 15-20 mg/m3 near an enterprise.

Sulfur dioxide irritates the mucous membranes of the upper respiratory tract. The threshold for olfactory sensation is a concentration of 2.6 mg/m 3 , the threshold for irritation is about 20 mg/m 3 .

Sulfur dioxide causes shifts in metabolic processes. High concentrations of it with prolonged exposure lead to the development of catarrh of the upper respiratory tract, bronchitis, and dyspeptic disorders. It is capable of causing hyperglycemia, which indicates its general toxic effect. Sulfur dioxide has a harmful effect on vegetation. In concentrations of 1:1,000,000 it causes damage visible to the eye in plants. With short-term exposure, sulfur dioxide at a concentration of 0.92 mg/m 3 affects the processes of plant assimilation, which does not occur at a concentration of 0.62 mg/m 3.

Carbon monoxide (CO). Carbon monoxide is an odorless and colorless gas. Density relative to air - 0.967. Carbon monoxide is formed during incomplete combustion of fuel; its formation is always associated with blast furnace, coke, gas generator and other industries. Carbon monoxide is found in significant quantities in lighting, water, smoke and exhaust gases. Along with smoke and gases emitted industrial enterprises, carbon monoxide enters the atmospheric air. The air on the highways of large cities may contain an increased amount of carbon monoxide due to vehicle exhaust gases (on average up to 10 mg/m3). At a distance of 1 km from the metallurgical plant, an average of 57 mg/m 3 of carbon monoxide was found in the atmospheric air.

Carbon monoxide is a blood and general toxic poison. The possibility of chronic carbon monoxide poisoning has been experimentally and clinically established. Observations show that the concentration of carbon monoxide of the order of 20-30 mg/m 3 can be taken as the threshold, beyond which disturbances in the body, in particular in the nervous system, are already observed.

Nitrogen oxides (NO, N 2 O 5, NO 2). Nitrogen oxides are a mixture of gases of variable composition. They easily combine with water vapor in the air and turn into nitrous and nitric acids.

Nitrogen oxides can enter the atmospheric air in significant quantities as emissions from industrial enterprises, during the production of nitric, sulfuric, oxalic and other acids, during blasting operations and can be determined quite long distance from enterprises (2.56 mg/m 3 at a distance of 1 km; 1.43 mg/m 3 at a distance of 2 km). With prolonged inhalation of small concentrations of nitrogen oxides, bronchitis, loss of nutrition, anemia, tooth decay, upset gastric secretion are observed, the tuberculosis process is activated, and the course of heart disease worsens.

Other gaseous impurities. Hydrogen sulfide (H2S) can be found in the atmospheric air, the source of which is industrial enterprises (chemical plants, metallurgical plants, oil refineries), processes of putrefactive decomposition of organic substances, accumulation of sewage, recycling plants, etc. In the latter case, the atmospheric air can be polluted by other products organic decomposition - ammonium sulphide, volatile fatty acids, indole, skatole, etc. Their presence, even in small quantities, is perceived by the sense of smell and causes unpleasant subjective sensations, sometimes leading to nausea and vomiting. The threshold for irritation is 14-20 mg/m3. A concentration of 0.04-0.012 mg/m3 is the threshold for the sensation of odor.

Plants for the production of carbon disulfide and viscose can be a source of atmospheric air pollution with carbon disulfide (a faint odor of carbon disulfide is felt at a concentration of 0.05 mg/m 3 of air). Atmospheric air can also be polluted with highly toxic substances (mercury vapor, lead, phosphorus, arsenic, etc.).

Mechanical impurities in the air

The atmospheric air of populated areas contains one or another amount of dust: terrestrial dust (soil, plant), sea, dust of cosmic origin, etc. But the main source of dust pollution in the atmospheric air is industrial enterprises (Fig. 11). Dust is an airborne system in which the dispersed phase is crushed solid matter and the dispersion medium is air. Dust can be organic (plant or animal origin), inorganic (metallic, mineral) and mixed. Mixed dust is usually observed in the atmospheric air.

The ability of dust particles to remain suspended in the air or fall out of it, settling with at different speeds, depends on their size and specific gravity. A speck of dust suspended in the air is exposed to two oppositely directed forces - gravity and friction. If gravity more power friction (dust particles larger than 10 microns in size), then the particles settle at an increasing speed; if the friction force balances the force of gravity (dust particles with a size of 10-0.1 microns), then they settle at a constant speed (Stokes’ law), and dust particles with a diameter less than 0.1 microns, as a rule, do not fall out of the dispersed system, being in constant Brownian motion.

The fate of dust in the respiratory tract is also related to the degree of dust dispersion, which thus determines its behavior in the air. Dust particles 10 microns in size and larger are retained in the upper respiratory tract (nose, nasopharynx, trachea, large bronchi), dust particles less than 10 microns penetrate the alveoli and linger there, having a pathological effect on the body depending on the nature of the dust. The greatest danger in this regard is dust with particle sizes less than 5 microns. Larger dust particles apparently fall out of the stream of inhaled air without reaching the alveoli. Dust particles less than 0.1 microns in size are retained in the lungs by 64-77%, and are not removed from them by the current of exhaled air, as was commonly believed.

At the same time, there are a number of circumstances that prevent dust from settling in the breathing apparatus: the difference in temperature between the inhaled air and the walls of the respiratory tract, the evaporation of moisture from these walls, which helps to repel dust particles, etc.

Near industrial enterprises, where dust protection installations (dust collection) are not used, the atmospheric air contains mainly small dust particles. Dust from power plants that pollutes the atmospheric air contains dust particles of the following sizes:

To characterize dust pollution in the air and hygienic assessment her important has the determination of the amount of dust contained in a certain volume of air. Quantitative characteristics are usually expressed in weight (gravimetric) indicators - in milligrams of dust per 1 m 3, air. Determining air dust content by counting dust particles in 1 cm 3 of air (conimetric method) currently has few supporters.

The maximum single concentrations of dust in the atmospheric air of industrial cities in the absence of treatment facilities can reach 1-3 mg/m3, and in some cases - 6.82 mg/m3.

According to R. A. Babayants, the maximum single concentrations of dust in the city he examined ranged from 0.84 to 13.85 mg/m 3 . According to the F. F. Erisman Institute of Hygiene, in one of the large cities the maximum one-time dust concentrations after ash collection measures were: in the city center 0.15-1.48 mg/m 3, in a residential area 0.22-1 .38 mg/m3, in the industrial area 0.67-1.93 mg/m3.

Hygienic characteristics of atmospheric air pollution

Gaseous substances and dust in atmospheric air, exceeding permissible levels, have a harmful effect on the body.

The products of incomplete combustion of coal and oil contain carcinogenic compounds that experimentally cause cancer in mice. A large number of carcinogenic substances have been found in coal tar, of which 3,4-benzpyrene, 1,2- and 5,6-dibenzanthracene are potent. Many authors associate the increase in the proportion of lung cancer among the urban population with the presence of carcinogenic substances in soot contained in the atmospheric air.

There are indications that lung cancer is 4 times more common in smoky areas of Cincinnati than in low-smoke areas. In the industrial cities of Germany and the USA, there is an increased incidence of respiratory diseases (pharyngitis, bronchitis, tracheitis), etc.

In known meteorological conditions, toxic fogs were observed due to the release of sulfur oxides into the atmosphere during fuel combustion, causing respiratory and cardiovascular disorders.

In December 1962, fog was observed in London, which was accompanied by increased mortality, especially among children early age and persons over 55 years of age. Observations showed that on foggy days from December 5 to 8, the concentration of soot and sulfur dioxide adsorbed by water vapor sharply increased in the atmospheric air (10 times more than usual).

From December 1 to December 5, 1930, near Liege (Belgium), several thousand cases of poisoning were recorded among the population, including 70 deaths, due to the fact that sulfur dioxide and hydrogen fluoride released into the air due to heavy fog reached dangerous concentrations. Urban air pollution is sometimes the result of photochemical reactions of hydrocarbons and nitrogen oxides.

Gaseous substances that pollute atmospheric air can cause chronic poisoning. The possibility of a decrease in the body’s resistance to infectious diseases as a result of prolonged inhalation of small concentrations of toxic substances in the atmospheric air. It is impossible not to take into account the harmful effects of unpleasant sensations associated with the spread of odors of gases such as carbon disulfide, hydrogen sulfide, sulfur dioxide and sulfuric anhydride, chlorine, etc., as well as the effect on the body of allergens, the presence of which in the atmospheric air in some cases is not excluded. The influence of aerosols of heavy metals (lead, zinc) cannot but affect the health of the population if they are constantly and in significant quantities present in the atmospheric air. It has been experimentally established that in the area of ​​emissions from a copper smelter, lead accumulates in the body of animals.

Atmospheric dust may contain a certain amount of free SiO 2 . Typically, the possibility of household silicosis occurring among the urban population is unlikely due to the relatively low dust content in urban air. However, in populated areas near powerful power plants, the possibility of presilicotic changes cannot be excluded.

To this we must add that the dust content in the atmospheric air of cities causes the loss of part of the solar radiation, which is absorbed by dust particles. Thus, the intensity of solar radiation in cities is 15-25% lower than in rural areas. This loss also occurs due to the ultraviolet part of solar radiation, due to rays with a wavelength from 315 to 290 mmk, which are of great importance for the growth and functioning of the body, especially in childhood. Through an experiment on white rats, it was established that the loss of 15-25% of ultraviolet rays leads to an increase in the level of phosphatase and a decrease in phosphorus, i.e., to phenomena that go in parallel with the severity of rickets.

The dust content of the atmospheric air reduces the overall illumination and contributes to the formation of fogs. Thus, diffused light illumination in industrial areas of a large city is 40-50% less than in its surroundings.

Dust impurities in the air can contribute to the formation of fogs due to their ability to transform into condensation nuclei of water vapor. As a result, the number of cloudy days in such an area increases, and consequently, the adverse impact of the climate on the population increases (lack of sunny days, decreased overall illumination, high air humidity, etc.).

In large cities, eye injuries are observed due to coal dust entering the eye.

Industrial emissions (dust, sulfur dioxide) have an adverse effect on vegetation, and this effect sometimes extends over very long (up to 25 km) distances from the enterprise.

Dust and soot contained in the atmospheric air penetrate into the home and, naturally, worsen sanitary conditions life of the population living in the area of ​​industrial emissions.

Measures for sanitary protection of atmospheric air. Concern for public health puts forward demands for combating air pollution.

Since the 30s of the 20th century, as a result of the rapid development of industry, a new direction in the hygiene of populated areas has been determined - sanitary protection of atmospheric air. A large amount of factual material accumulated as a result of research formed the basis for advanced Soviet legislation on protecting the cleanliness of the air in industrial cities. For this purpose, control has been established to ensure compliance with hygienic standards of maximum permissible concentrations (MPC) of pollutants in the atmospheric air.

The All-Union State Sanitary Inspectorate approved the maximum permissible concentrations of substances in the atmospheric air of populated areas (Table 4).

The maximum permissible concentration of a harmful substance is considered to be such a concentration at which the adverse effects of this substance on the body are excluded for an indefinitely long time. There is a distinction between a one-time maximum permissible concentration, which means the highest concentration determined by short-term (15-20 minutes) sampling, and an average daily concentration - the arithmetic mean of many samples taken during the day. Ensuring air purity at the level of the given maximum permissible concentrations in the atmospheric air of industrial cities requires sanitary and hygienic measures. A radical solution to this problem is unthinkable in capitalist countries, where industrial enterprises belong to the bourgeoisie, which is not interested in carrying out these sometimes expensive measures. In the Soviet Union, enormous work is being done to protect the sanitary air. To ensure the purity of atmospheric air, measures to combat emissions from boiler houses, power plants and combined heat and power plants, control of vehicle exhaust gases, district heating of cities, eliminating the need for small boiler plants, their gasification, which contributes to a significant reduction in soot pollution of the atmosphere, and electrification are of great importance. railway transport, recovery (return of materials or energy used once during a process for reuse in this process) of industrial emissions, etc.

Sanitary measures are aimed at ensuring the purification of industrial emissions from dust and gases that pollute the atmospheric air. To collect dust and ash, there are various devices from simple ones (dust settling chambers) to more or less complex ones (cyclone, multicyclone, various types of ash collectors, etc.).

Air purification in cyclones (Fig. 12) and multicyclones (Fig. 13) is carried out as follows. Passing through these devices, the air receives a rotational movement. As a result of the resulting centrifugal force, dust particles are thrown towards the walls of the cyclone, fall out of the air and accumulate in the lower part of the device, from where they are removed. The air purification coefficient in a cyclone is usually 40-50%, in a multicyclone - 63%. The wet ash collector is more efficient (92-98%). Finally, electric precipitators are highly efficient devices for ash and dust collection (Fig. 14). They are based on the following principle. When dusty air passes through a tube connected to the positive pole of a direct current, in the center of which there is a wire connected to the negative pole, the dust particles acquire a negative charge, are thrown towards the walls of the tube, lose their charge and fall out of the air.

Several methods have been proposed for desulfurization (magnesite, lime, ammonia, etc.) based on the capture of sulfur dioxide, and the most advanced of them make it possible to purify the air from sulfur dioxide by 98-99%. Important measures to protect atmospheric air include prohibiting the construction of enterprises in residential areas that pollute the atmospheric air, placing them on special industrial sites, taking into account the direction of prevailing winds, and complying with established regulations. sanitary standards(CH 245-63) gaps between industrial enterprises and residential areas, widespread and massive greening of cities, their improvement and rational sanitary cleaning.