The oxygen content in the air is. The chemical composition of atmospheric air and its hygienic significance

The atmospheric air that enters the lungs during inhalation is called inhaled air; air released to the outside through the respiratory tract during exhalation - exhaled... The exhaled air is a mixture of air filling out alveoli, - alveolar air - with air in the airways (in the nasal cavity, larynx, trachea and bronchi). The composition of the inhaled, exhaled and alveolar air in normal conditions in a healthy person is fairly constant and is determined by the following figures (Table 3).

These figures may fluctuate somewhat depending on various conditions (state of rest or work, etc.). But under all conditions, alveolar air differs from inhaled air in a significantly lower oxygen content and a higher carbon dioxide content. This is due to the fact that oxygen enters the bloodstream from the air in the pulmonary alveoli, and carbon dioxide is released back.

Gas exchange in the lungs due to the fact that in pulmonary alveoli and venous bloodflowing to the lungs, oxygen and carbon dioxide pressure different: the oxygen pressure in the alveoli is higher than in the blood, and the pressure of carbon dioxide, on the contrary, in the blood is higher than in the alveoli. Therefore, in the lungs, oxygen is transferred from air to blood, and carbon dioxide is transferred from blood to air. Such a transition of gases is explained by certain physical laws: if the pressure of any gas in the liquid and in the air surrounding it is different, then the gas passes from liquid to air and vice versa until the pressure equilibrates.

Table 3

In a mixture of gases, which is air, the pressure of each gas is determined by the percentage of this gas and is called partial pressure (from the Latin word pars - part). For example, atmospheric air exerts a pressure equal to 760 mm Hg. The oxygen content in the air is 20.94%. The partial pressure of oxygen in atmospheric air will be 20.94% of the total air pressure, i.e. 760 mm, and equal to 159 mm Hg. It has been established that the partial pressure of oxygen in the alveolar air is 100 - 110 mm, and in the venous blood and capillaries of the lungs - 40 mm. The partial pressure of carbon dioxide is 40 mm in the alveoli, and 47 mm in the blood. The difference in the partial pressure between the gases of blood and air explains gas exchange in the lungs. In this process, the cells of the walls of the pulmonary alveoli and the blood capillaries of the lungs, through which gases pass, play an active role.

Air - a mixture of gases, mainly nitrogen and oxygen, which make up the atmosphere of the globe.Total air mass is 5.13 × 10 15 t and exerts pressure on the Earth's surface, equal to an average of 1.0333 at sea level kgby 1 cm 3... Weight 1 ldry air free of water vapor and carbon dioxide, under normal conditions is 1.2928 r, specific heat - 0.24, thermal conductivity coefficient at 0 ° - 0.000058, viscosity - 0.000171, refractive index - 1.00029, water solubility 29.18 ml by 1 lwater. Composition of atmospheric air - see table ... Atmospheric air also contains water vapor and impurities (solid particles, ammonia, hydrogen sulfide, etc.) in various quantities.

Composition of atmospheric air

For a person, a vital component B is oxygen, the total mass of which is 3.5 × 10 15 t... In the process of restoring the normal oxygen content, the main role is played by photosynthesis by green plants, the initial substances for which are carbon dioxide and water. The transfer of oxygen from atmospheric air to blood and from blood to tissue depends on the difference in its partial pressure, therefore, the partial pressure of oxygen is of biological importance, and not its percentage in V. At sea level, the partial pressure of oxygen is 160 mm... When you reduce it to 140 mm the person has the first signs hypoxia. Decrease in partial pressure to 50-60 mm life-threatening (see. Altitude sickness, Mountain sickness).

Bibliography: The atmosphere of the earth and planets, ed. D.P. Kuiper. per. from English, M., 1951; Gubernskiy Yu.D. and Korenevskaya E.I. Hygienic bases of microclimate conditioning of residential and public buildings, M., 1978; Minkh A.A. Ionization of air and its hygienic value, M., 1963; Guide to air hygiene, ed. K.A. Bushtueva, M., 1976; Guide to Communal Hygiene, ed. F.G. Krotkova, vol. 1, p. 137, M., 1961.

AIR is a mixture of gases that forms the atmosphere, a shell around the globe, which makes it possible for animals and plant organisms to live on Earth.

Air consists mainly of a mixture of nitrogen (78.09% by volume) and oxygen (20.95% by volume); all other gases account for about 1%. The most important component of air is oxygen, which plays a major role in maintaining life on Earth. In the process of vital activity, animal organisms continuously consume oxygen. Replenishment of B.'s oxygen reserves occurs due to the production of it by plants, the green parts of which absorb carbon dioxide in the light during photosynthesis and use its carbon to form organic matter, while releasing free oxygen into the air. Thus, in nature there is a circulation of oxygen, during which, simultaneously with a large consumption of oxygen, a complete restoration of its amount occurs.

A person inhales 20-30 cubic meters per day. air. A person's need for oxygen depends on the intensity of labor activity; at rest, this requirement is 25 liters per hour. Reducing the oxygen content in the air to 16-18% does not have a noticeable effect on the human body; a decrease to 14% is already accompanied by symptoms of oxygen deficiency, and a decrease to 9% is life-threatening. However, the main biological significance is not the percentage of oxygen in the air, but its partial (partial) pressure, that is, that part of the total atmospheric pressure that falls on its share, since the transfer of oxygen from the air contained in the alveoli of the lungs to the blood and tissues based on the difference in its partial pressure. This transition is most fully carried out at a partial pressure of oxygen in the atmospheric air equal to 150-159 mm, which usually takes place at an atmospheric pressure of 760 mm. The partial pressure of oxygen in alveolar air is lower than in atmospheric air: at a partial pressure of oxygen in atmospheric air equal to 159 mm, in alveolar air it is only 105 mm. A decrease in the partial pressure of oxygen in the air entails a violation of the respiratory process, a decrease in pulmonary and tissue gas exchange, depletion of blood and tissues with oxygen. With a decrease in the partial pressure of oxygen in the atmospheric air to 130-140 mm (in the alveolar air, respectively, up to 80-85 mm), a number of disorders may already occur - shortness of breath, increased frequency and depth of breathing, increased heart rate, accelerated blood flow and others that are worn compensatory character. With a further decrease in the partial pressure of oxygen to 110 mm (in the alveolar air - about 62 mm), the compensatory capabilities of the body are already insufficient and the phenomena of oxygen deficiency appear (the so-called hypoxemia, hypoxia). A further decrease in the partial pressure of oxygen to 50-60 mm (in alveolar air up to 20-25 mm) can lead to death. Oxygen deficiency can be compensated by drinking an oxygen cocktail. An oxygen cocktail is prepared using various devices, including an oxygen concentrator, oxygen mixers, aroma stations, foaming agents and many others.

A decrease in the partial pressure of oxygen is noted with an increase in altitude. Therefore, when climbing mountains or on an airplane with an unpressurized cockpit, low-trained and non-acclimatized people can develop the so-called altitude sickness. It is much easier for the body to tolerate an increase in the oxygen content in the inhaled air. Experimental animals tolerate an oxygen content of 40-60% in the air for a long time without any noticeable manifestations and disturbances in the state of the organism. In diving operations, breathing air containing up to 50% oxygen is also tolerated without harmful consequences.

With a high partial pressure of oxygen (about 1 atm) and prolonged inhalation of oxygen, edema and inflammation of the lungs develop.

The second important constituent of air is nitrogen. It belongs to inert gases and is not able to sustain breathing and combustion. However, nitrogen plays an important role as a diluent of oxygen in the atmospheric air, providing a concentration of oxygen in the air favorable for maintaining normal respiration of animals and humans. The best conditions for life are created when the air contains 78.09% nitrogen (by volume) and 20.95% oxygen. With an increase in the nitrogen content in the air to 83%, the first signs of oxygen deficiency are noted. Nitrogen at its increased partial pressure in the inhaled air has a narcotic effect (at a partial nitrogen pressure of 30-40 atm, complete anesthesia occurs). The study of the toxic effect of nitrogen in divers during deep-sea descents showed that when breathing ordinary air under a pressure of 9 atm or more, a number of disorders are noted. Nitrogen dissolves in the blood and body tissues in quantities proportional to its partial pressure. With the rapid transition of a person from high pressure to low pressure, excess nitrogen is released from tissues and blood in the form of gas bubbles, which is the cause of the so-called decompression sickness.

Carbon dioxide (CO2) is a constant part of the air. Carbon dioxide is involved in the carbon cycle; it is absorbed in large quantities by plants. However, its amount in the air remains constant due to its intake from the soil, in the composition of industrial gases and smoke, due to the respiration of people and animals. A person at rest exhales 22.6 liters of CO2 in 1 hour. The largest amount of CO2 is found in the air of large industrial cities. The smallest amount is above the water surface of the oceans and seas. The regulating effect on the CO2 content in the atmospheric air is exerted by the water of the seas and oceans, which, depending on the value of the partial pressure of atmospheric oxygen and temperature, gives or absorbs CO2 from the atmospheric air. The physiological significance of carbon dioxide lies in its stimulating effect on the respiratory center. Since in the process of vital activity in the body, carbon dioxide is formed in an amount sufficient to create the necessary partial pressure of CO2 in the blood, ensuring the normal course of the respiratory process, a decrease in the content of carbon dioxide in the atmospheric air is not significant. An increase in the concentration of CO2 in the air affects the state of the body: when the concentration of CO2 in the air is 3-4%, breathing accelerates and deepens, there is a headache, tinnitus, a slowdown in the pulse, an increase in blood pressure, etc., with an increase in the concentration of CO2 in the air up to 10 % loss of consciousness and death may occur. The mechanism of action of high concentrations of CO2 is similar to the action of oxygen deficiency. The hygienic standard for the CO2 content in the air of residential and public buildings is considered to be 0.1%. Carbon dioxide is commonly regarded as an indicator of indoor air pollution.

Ozone (O3) should be noted from other air gases, which belongs to active gases that have an impact on human health. However, the natural ozone content at the earth's surface is negligible and does not pose any health hazard. The largest amounts of ozone are concentrated in the atmosphere at an altitude of 25-30 km. Ozone plays an important role in protecting against the harmful effects of short waves of solar radiation, and also has the ability to trap heat emanating from the ground and, thus, to some extent inhibits the cooling of the earth's surface.

The air can also contain other gases in the form of impurities, including harmful ones (hydrogen sulfide, sulfur dioxide, ammonia, carbon monoxide and others), which most often occurs near industrial enterprises. Among air pollutants, the first place belongs to dust... Measures for the sanitary protection of air are aimed at the utmost reduction in the content of these harmful impurities in the air.
In addition to the composition of the air, physical properties of air are also essential for normal human life: temperature, humidity, mobility, which have a combined effect on the body, increasing or decreasing its heat transfer. The most favorable air temperature for humans is 18-20 °. The harder the work performed by a person, the lower the air temperature should be. A person easily tolerates temperature fluctuations, due to his inherent ability to .

Air humidity is of great importance for the normal well-being of a person. The most favorable for humans is a relative humidity of 40-60%. Dry air is well tolerated by humans, high humidity acts extremely unfavorably: at high air temperatures, it contributes to overheating of the body, since it makes it difficult to evaporate sweat, and at low temperatures it contributes to hypothermia, since humid air is characterized by high thermal conductivity. A person is very sensitive to air movement, which causes an increase in heat transfer from the body. At low temperatures, the wind contributes to the rapid hypothermia of the body. At high temperatures or intense sun, the wind protects against overheating, improves well-being.

The air can contain microorganisms, including pathogens. The air polluted by them can contribute to the spread of some infectious diseases, especially the so-called droplet infections (flu, diphtheria, measles, scarlet fever, whooping cough, and others), the pathogens of which a sick person secretes with droplets of saliva and mucus when coughing, sneezing, talking.

It is always necessary to monitor the cleanliness of the air in the room: systematically wash the floors, ventilate the rooms by arranging drafts, carefully pump out dust from upholstered furniture, carpets, curtains, bedding and clothing at least once a week.

Let's make a reservation right away, nitrogen in the air takes up most of it, however, the chemical composition of the remaining fraction is very interesting and diverse. In short, the list of basic elements is as follows.

However, we will give a small explanation of the functions of these chemical elements.

1. Nitrogen

The nitrogen content in the air is 78% by volume and 75% by mass, that is, this element dominates the atmosphere, has the title of one of the most widespread on Earth, and, in addition, it is also contained outside the human habitat - on Uranus, Neptune and in interstellar spaces. So, how much nitrogen is in the air, we have already figured out, the question remains about its function. Nitrogen is necessary for the existence of living things, it is part of:

• proteins;
• amino acids;
• nucleic acids;
• chlorophyll;
• hemoglobin, etc.

On average, about 2% of a living cell are just nitrogen atoms, which explains why there is so much nitrogen in the air as a percentage of volume and mass.
Nitrogen is also one of the inert gases produced from atmospheric air. Ammonia is synthesized from it, used for cooling and for other purposes.

2. Oxygen

The oxygen content in the air is one of the most popular questions. Keeping the intrigue, let us digress into one fun fact: oxygen was discovered twice - in 1771 and 1774, however, due to the difference in the publication of the discovery, the honors of the discovery of the element went to the English chemist Joseph Priestley, who actually gave oxygen the second. So, the proportion of oxygen in the air fluctuates around 21% by volume and 23% by mass. Together with nitrogen, these two gases form 99% of all earth's air. However, the percentage of oxygen in the air is less than nitrogen, and we do not experience breathing problems. The fact is that the amount of oxygen in the air is optimally calculated precisely for normal breathing, in its pure form this gas acts on the body like a poison, leads to difficulties in the functioning of the nervous system, failures in breathing and blood circulation. At the same time, the lack of oxygen also negatively affects health, causing oxygen starvation and all the unpleasant symptoms associated with it. Therefore, how much oxygen is contained in the air, so much is needed for healthy breathing.

3. Argon

Argon ranks third in the air, it is odorless, colorless and tasteless. A significant biological role of this gas has not been identified, however, it has a narcotic effect and is even considered doping. Argon extracted from the atmosphere is used in industry, medicine, for creating an artificial atmosphere, chemical synthesis, fire extinguishing, creating lasers, etc.

4. Carbon dioxide

Carbon dioxide makes up the atmosphere of Venus and Mars, its percentage in the earth's air is much lower. At the same time, a huge amount of carbon dioxide is contained in the ocean, it is regularly supplied by all breathing organisms, and is emitted due to the work of industry. In human life, carbon dioxide is used in fire extinguishing, in the food industry as a gas and as a food additive E290 - a preservative and baking powder. In solid form, carbon dioxide is one of the most famous dry ice refrigerants.

5. Neon

The same mysterious light of disco lights, bright signs and modern headlights use the fifth most common chemical element that humans also inhale - neon. Like many inert gases, neon has a narcotic effect on a person at a certain pressure, but it is this gas that is used in the training of divers and other people working at elevated pressure. Also, neon-helium mixtures are used in medicine for respiratory disorders, neon itself is used for cooling, in the production of signal lights and those same neon lamps. However, contrary to the stereotype, neon light is not blue, but red. All other colors are produced by lamps with other gases.

6. Methane

Methane and air have a very ancient history: in the primary atmosphere, even before the appearance of man, methane was in much greater quantities. Today, this gas, produced and used as a fuel and raw material in production, is not as widespread in the atmosphere, but it still escapes from the Earth. Modern studies establish the role of methane in respiration and vital activity of the human body, but there is no authoritative data on this yet.

7. Helium

By looking at how much helium is in the air, anyone will understand that this gas is not among the first in importance. Indeed, it is difficult to determine the biological significance of this gas. Apart from the funny distortion of the voice when inhaling helium from a balloon 🙂 However, helium is widely used in industry: in metallurgy, food industry, for filling aeronautic ships and meteorological probes, in lasers, nuclear reactors, etc.

8. Krypton

We are not talking about the homeland of Superman 🙂 Krypton is an inert gas that is three times heavier than air, chemically inert, extracted from the air, used in incandescent lamps, lasers and is still actively studied. Of the interesting properties of krypton, it is worth noting that at a pressure of 3.5 atmospheres it has a narcotic effect on a person, and at 6 atmospheres it acquires a pungent smell.

9. Hydrogen

Hydrogen in the air occupies 0.00005% by volume and 0.00008% by mass, but at the same time it is he who is the most abundant element in the Universe. It is quite possible to write a separate article about its history, production and application, so now we will restrict ourselves to a small list of industries: chemical, fuel, food industries, aviation, meteorology, and power engineering.

10. Xenon

The latter is in the composition of air, and was originally considered only an admixture of krypton. Its name translates as "alien", and the percentage of content both on Earth and beyond is minimal, which led to its high cost. Nowadays they cannot do without xenon: the production of powerful and pulsed light sources, diagnostics and anesthesia in medicine, spacecraft engines, rocket fuel. In addition, when inhaled, xenon significantly lowers the voice (the opposite effect to helium), and recently inhalation of this gas has been included in the list of doping.

Atmospheric air, which a person breathes in outside the room (or in well-ventilated rooms), contains 20.94% oxygen, 0.03% carbon dioxide, 79.03% nitrogen. In closed spaces filled with people, the percentage of carbon dioxide in the air can be slightly higher.

Exhaled air contains on average 16.3% oxygen, 4% carbon dioxide, 79.7% nitrogen (these figures are given in terms of dry air, that is, minus water vapor, which is always saturated with exhaled air).

Exhaled air composition very fickle; it depends on the intensity of the body's metabolism and on the volume of pulmonary ventilation. It is worth making a few deep breathing movements or, on the contrary, holding your breath so that the composition of the exhaled air changes.

Nitrogen does not participate in gas exchange, however, the percentage of nitrogen in visible air is several tenths of a percent higher than in inhaled air. The fact is that the volume of exhaled air is somewhat less than the volume of inhaled air, and therefore the same amount of nitrogen, being distributed in a smaller volume, gives a larger percentage. The smaller volume of exhaled air in comparison with the volume of inhaled air is explained by the fact that carbon dioxide is released slightly less than oxygen is absorbed (part of the absorbed oxygen is used in the body to circulate compounds that are excreted from the body in urine and sweat).

Alveolar air differs from exhaled by a large percentage of non-acid and a lower percentage of oxygen. On average, the composition of the alveolar air is as follows: oxygen 14.2-14.0%, carbon dioxide 5.5-5.7%, nitrogen about 80%.

Definition alveolar air compositionimportant for understanding the mechanism of gas exchange in the lungs. Holden proposed a simple method for determining the composition of the alveolar air. After a normal inhalation, the subject makes as deep an exhalation as possible through a tube 1-1.2 m long and 25 mm in diameter. The first portions of exhaled air leaving through the tube contain harmful air; the last portions remaining in the tube contain alveolar air. For analysis, air is taken into the gas receiver from that part of the tube that is closest to the mouth.

The composition of the alveolar air differs slightly depending on whether the air sample is taken for analysis at the inspiratory or expiratory height. If you make a quick, short and incomplete exhalation at the end of a normal inhalation, the air sample will reflect the composition of the alveolar air after the lungs are filled with breathing air, that is, during inhalation. If you make a deep exhalation after a normal exhalation, the sample will reflect the composition of the alveolar air during exhalation. It is clear that in the first case, the percentage of carbon dioxide will be slightly less, and the percentage of oxygen is slightly higher than in the second. This can be seen from the results of Holden's experiments, who found that the percentage of carbon dioxide in the alveolar air at the end of inhalation is on average 5.54, and at the end of exhalation - 5.72.

Thus, there is a relatively small difference in the content of carbon dioxide in the alveolar air during inhalation and exhalation: only 0.2-0.3%. This is largely due to the fact that during normal breathing, as mentioned above, only 1/7 of the air volume in the pulmonary alveoli is renewed. The relative constancy of the composition of the alveolar air is of great physiological importance, which is explained below.