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

Atmospheric air entering the lungs during inhalation is called inhaled air; air expelled through Airways while exhaling, exhaled. Exhaled air is a mixture of air filling alveoli, - alveolar air- with air in the airways (in the nasal cavity, larynx, trachea and bronchi). The composition of inhaled, exhaled and alveolar air under normal conditions in a healthy person is quite constant and is determined by the following figures (Table 3).

These figures may vary slightly depending on various conditions(state of rest or work, etc.). But under all conditions, the alveolar air differs from the inhaled air by a significantly lower content of oxygen and a higher content of carbon dioxide. This happens as a result of the fact that in the pulmonary alveoli, oxygen enters the blood from the air, and carbon dioxide is released back.

Gas exchange in the lungs due to the fact that in lung alveoli and venous blood flowing to the lungs, pressure of oxygen and carbon dioxide different: the pressure of oxygen 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 a gas in a liquid and in the air surrounding it is different, then the gas passes from liquid to air and vice versa until the pressure is balanced.

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%. Partial pressure of oxygen atmospheric air will be 20.94% of the total air pressure, i.e. 760 mm, and equal to 159 mm of mercury. 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 partial pressure between blood and air gases explains gas exchange in the lungs. In this process, the cells of the walls of the pulmonary alveoli play an active role and blood capillaries lungs through which gases pass.

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

Composition of atmospheric air

Vital for a person integral part 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 tissues depends on the difference in its partial pressure, therefore biological significance has a partial pressure of oxygen, not a percentage of it in V. At sea level, the partial pressure of oxygen is 160 mm. When it drops to 140 mm a person shows the first signs hypoxia. Reduced partial pressure to 50-60 mm life-threatening (cf. Altitude sickness, Mountain sickness).

Bibliography: Atmosphere of the Earth and Planets, ed. D.P. Kuiper. per. from English, M., 1951; Gubernsky Yu.D. and Korenevskaya E.I. Hygienic basics of microclimate conditioning of residential and public buildings, M., 1978; Minkh A.A. Air ionization and its hygienic value, M., 1963; Guidelines for atmospheric 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 plants to live on Earth.

Air consists primarily 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 life, animals continuously consume oxygen. V.'s oxygen supply is replenished by its production by plants, the green parts of which, in the process of photosynthesis, absorb carbon dioxide in the light and use its carbon to form organic substances, 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, full recovery its quantity.

A person inhales 20-30 cubic meters per day. air. The human need for oxygen depends on the intensity labor activity; at rest, this need 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 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 transition 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 complete at a partial pressure of oxygen in 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. Lowering 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 and increased depth of breathing, increased heart rate, acceleration of blood flow, and others that are 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 no longer sufficient and oxygen deficiency occurs (the so-called hypoxemia, hypoxia). A further decrease in the partial pressure of oxygen to 50-60 mm (in the alveolar air up to 20-25 mm) can lead to death. Oxygen deficiency can be compensated by using an oxygen cocktail. The preparation of an oxygen cocktail is carried out using various devices, including an oxygen concentrator, oxygen mixers, aromatic stations, foam concentrates, 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 cabin, poorly trained and unacclimatized people may develop the so-called altitude sickness. The body tolerates an increase in the oxygen content in the inhaled air much easier. Experimental animals tolerate the oxygen content in the air of 40-60% for a long time without any noticeable manifestations and disturbances in the state of the body. When diving, 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 it, 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 support breathing and combustion. However, nitrogen plays an important role as an oxygen diluent in the atmospheric air, providing a favorable oxygen concentration in the air for maintaining normal respiration of animals and humans. Best conditions for life are created when the content of nitrogen in the air is 78.09% (by volume) and oxygen is 20.95%. With an increase in the nitrogen content in the air up 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). Study of toxic action nitrogen in divers during deep-sea descents showed that when breathing ordinary air at a pressure of 9 atm or more, a number of disorders are noted. Nitrogen dissolves in the blood and body tissues in amounts proportional to its partial pressure. With the rapid transition of a person from high to low pressure, excess nitrogen is released from the tissues and blood in the form of gas bubbles, which is the cause of the so-called decompression sickness.

A constant constituent of air is carbon dioxide (CO2). Carbon dioxide is involved in the carbon cycle; it is absorbed into in large numbers plants. However, its amount in the air remains constant due to its intake from the soil, as part of industrial gases and smoke, and 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 contained in the air of large industrial cities. The smallest amount is above the water surface of the oceans and seas. The water of the seas and oceans has a regulating influence on the content of CO2 in the atmospheric air, which, depending on the partial pressure of oxygen in the air 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 carbon dioxide is formed in the body in the course of life in an amount sufficient to create the necessary partial pressure of CO2 in the blood, which ensures the normal course of the respiratory process, a decrease in the carbon dioxide content in the atmospheric air is not significant. An increase in the concentration of CO2 in the air affects the state of the body: with a content of 3-4% CO2 in the air, breathing accelerates and deepens, headaches, tinnitus, slowing of the pulse, increase in blood pressure and another, 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 that of oxygen deficiency. The hygienic standard for the content of CO2 in the air of residential and public spaces considered to be 0.1%. Carbon dioxide is commonly regarded as an indicator of indoor air pollution.

Of the other air gases, ozone (O3) should be noted, which is one of the active gases that affect human health. However, the natural ozone content at the earth's surface is negligible and does not pose any health hazard. Largest Quantities ozone is 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. solar radiation, and also has the ability to retain heat emanating from the earth and, thus, to some extent prevents the cooling of the earth's surface.

Other gases, including harmful ones (hydrogen sulfide, sulfur dioxide, ammonia, carbon monoxide, and others), can be in the air in the form of impurities, which most often occurs near industrial enterprises. Among the impurities that pollute the air, the first place belongs to dust. Measures for the sanitary protection of air are aimed at the overall reduction of the content of these harmful impurities in the air.
In addition to the composition of the air, essential for normal human life are also physical properties air: temperature, humidity, mobility, which have a combined effect on the body, increasing or decreasing its heat transfer. The most favorable air temperature for a person 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 a person relative humidity of 40-60%. Dry air is well tolerated by humans, high humidity is extremely unfavorable: high temperature air, it contributes to overheating of the body, as it makes it difficult for sweat to evaporate, and when low temperatures contributes to its hypothermia, as wet air has a high thermal conductivity. A person is very sensitive to the movement of air, 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 may contain microorganisms, including pathogens. The air polluted by them can contribute to the spread of some contagious diseases, especially the so-called drop infections (flu, diphtheria, measles, scarlet fever, whooping cough, and others), the causative agents of which are excreted by a sick person 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 drafting, carefully knock out the 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 most, however, the chemical composition of the remaining fraction is very interesting and diverse. In short, the list of main elements is as follows.

However, we will also give some explanations on the functions of these chemical elements.

1. Nitrogen

The content of nitrogen in the air is 78% by volume and 75% by mass, that is, this element dominates in the atmosphere, has the title of one of the most common on Earth, and, in addition, is found outside the human habitation zone - 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 beings, it is part of:

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

On average, about 2% of a living cell is 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 extracted 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's digress for one fun fact: oxygen was discovered twice - in 1771 and 1774, however, due to the difference in publications of the discovery, the credit for the discovery of the element went to the English chemist Joseph Priestley, who actually isolated oxygen 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 the earth's air. However, the percentage of oxygen in the air is less than nitrogen, and yet we do not experience breathing problems. The fact is that the amount of oxygen in the air is optimally calculated specifically for normal breathing, in its pure form this gas acts on the body like a poison, leads to difficulties in work nervous system, respiratory and circulatory failures. 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 full breathing.

3. Argon

Argon in the air takes the third place, it has no smell, color and taste. meaningful biological role this gas has not been identified, but 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 fighting, 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. Wherein great amount 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 fighting, 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 well-known refrigerants in dry ice.

5. Neon

The same mysterious light of disco lights, bright signs and modern headlights use the fifth most common chemical element that people 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 preparation of divers and other people working under pressure. high blood 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 very neon lamps. However, contrary to the stereotype, neon light is not blue, but red. All other colors give lamps with other gases.

6. Methane

Methane and air have very ancient history: in the primary atmosphere, even before the appearance of man, methane was in far more. Now this gas, extracted and used as a fuel and raw material in production, is not so widely distributed in the atmosphere, but is still emitted from the Earth. Modern research establish the role of methane in the respiration and life of the human body, but there are no authoritative data on this subject yet.

7. Helium

Looking at how much helium is in the air, anyone will understand that this gas is not one of the most important in importance. Indeed, it is difficult to determine the biological significance of this gas. Not counting the funny voice distortion when inhaling helium from a balloon 🙂 However, helium is widely used in industry: in metallurgy, food industry, for filling balloons and meteorological probes, in lasers, nuclear reactors, etc.

8. Krypton

We are not talking about the birthplace of Superman 🙂 Krypton is an inert gas that is three times heavier than air, chemically inert, extracted from air, used in incandescent lamps, lasers and is still being actively studied. From interesting properties 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 odor.

9. Hydrogen

Hydrogen in the air occupies 0.00005% by volume and 0.00008% by mass, but at the same time it 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 limit ourselves to a small list of industries: chemical, fuel, food industry, aviation, meteorology, electric power industry.

10. Xenon

The latter is in the composition of air, which was originally considered to be only an admixture to krypton. Its name translates as "alien", and the percentage of content both on Earth and beyond is minimal, which led to its high cost. Now xenon is essential: 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 of helium), and more recently, inhalation of this gas has been added to the doping list.

atmospheric air, which a person inhales while outdoors (or in well-ventilated rooms), contains 20.94% oxygen, 0.03% carbon dioxide, 79.03% nitrogen. In enclosed spaces filled with people, the percentage of carbon dioxide in the air can be slightly higher.

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

Composition of exhaled air very fickle; it depends on the intensity of the body's metabolism and on the volume of pulmonary ventilation. It is worth taking 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, distributed in a smaller volume, gives a larger percentage. The smaller volume of exhaled air compared to the volume of inhaled air is due to the fact that slightly less carbon dioxide is released than oxygen is absorbed (part of the absorbed oxygen is used in the body to circulate compounds that are excreted from the body with urine and sweat).

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

Definition composition of alveolar air important for understanding the mechanism of gas exchange in the lungs. Holden proposed a simple method for determining the composition of alveolar air. After a normal inhalation, the subject exhales as deeply 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 the air of the harmful space; 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 varies somewhat depending on whether the air sample was taken for analysis at the height of inhalation or exhalation. If you make a quick, short and incomplete expiration at the end of a normal inspiration, then the air sample will reflect the composition of the alveolar air after filling the lungs with respiratory air, i.e. during inspiration. If you take a deep breath after a normal exhalation, then 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 somewhat less, and the percentage of oxygen will be somewhat greater 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 inspiration is on average 5.54, and at the end of expiration - 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 volume of air in the pulmonary alveoli is renewed. The relative constancy of the composition of the alveolar air is of great physiological importance, as will be explained below.