Air composition as a percentage in the city. How many percent of oxygen is in atmospheric air. Basic elements of the atmosphere
Atmospheric air, which is inhaled by a person outside the room (or in a well-ventilated area), contains 20.94% oxygen, 0.03% carbon dioxide, 79.03% nitrogen. In closed rooms 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 slightly less than the volume of inhaled, and therefore the same amount of nitrogen, being distributed in a smaller volume, gives a larger percentage. The smaller volume of exhaled air compared to 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 was 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 the experiments of Holden, who found that the percentage of carbon dioxide in the alveolar air at the end of inhalation averages 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 significance, which is explained below.
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 by 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 poison, leads to difficulties in work nervous system, breathing and blood circulation 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 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 ๐ 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 ๐ 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 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 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.
The air that makes up the earth's atmosphere is a mixture of gases. Dry atmospheric air contains: oxygen 20.95%, nitrogen 78.09%, carbon dioxide 0.03%. In addition, the atmospheric air contains argon, helium, neon, krypton, hydrogen, xenon and other gases. Ozone, nitrogen oxide, iodine, methane, water vapor are present in small amounts in the atmospheric air.
In addition to the permanent constituents of the atmosphere, it contains a variety of pollution introduced into the atmosphere by human production activities.
1. An important component of atmospheric air is oxygen , the amount of which in the earth's atmosphere is 1.18 ยท 10 15 tons. The constant oxygen content is maintained due to continuous processes of its exchange in nature. On the one hand, oxygen is consumed during the respiration of humans and animals, is spent on maintaining combustion and oxidation processes, on the other hand, it enters the atmosphere due to the processes of photosynthesis of plants. Land plants and oceans phytoplankton completely restore natural oxygen loss. With a drop in the partial pressure of oxygen, the phenomenon of oxygen starvation can develop, which is observed when climbing to a height. The critical level is oxygen partial pressure below 110 mm Hg. Art. Decrease in the partial pressure of oxygen to 50-60 mm Hg. Art. usually incompatible with life. Under the influence of short-wave UV radiation with a wavelength of less than 200 nm, oxygen molecules dissociate to form atomic oxygen. The newly formed oxygen atoms attach to the neutral oxygen formula, forming ozone ... Simultaneously with the formation of ozone, it decays. The general biological significance of ozone is great: it absorbs short-wave UV radiation, which has a destructive effect on biological objects. At the same time, ozone absorbs infrared radiation emanating from the Earth, and thus prevents excessive cooling of its surface. Ozone concentrations are unevenly distributed over height. Its greatest amount is observed at the level of 20-30 km from the Earth's surface.
2. Nitrogen quantitatively, it is the most essential component of atmospheric air, it belongs to inert gases. Life is impossible in a nitrogen atmosphere. Air nitrogen is assimilated by some types of soil bacteria (nitrogen-fixing bacteria), as well as blue-green algae; under the influence of electrical discharges, it turns into nitrogen oxides, which, falling out with atmospheric precipitation, enrich the soil with salts of nitrous and nitric acids. Under the influence of soil bacteria, nitrous acid salts are converted into nitric acid salts, which in turn are absorbed by plants and serve for protein synthesis. Along with the assimilation of nitrogen in nature, it is released into the atmosphere. Free nitrogen is formed during the combustion of wood, coal, oil; a small amount is formed by the decomposition of organic compounds. Thus, in nature, there is a continuous circulation, as a result of which atmospheric nitrogen is converted into organic compounds, restored and enters the atmosphere, and then re-bound by biological objects.
Nitrogen is necessary as an oxygen diluent, since breathing pure oxygen leads to irreversible changes in the body.
However, the increased nitrogen content in the inhaled air contributes to the onset of hypoxia due to a decrease in the partial pressure of oxygen. With an increase in the nitrogen content in the air to 93%, death occurs.
In addition to nitrogen, inert gases of air include argon, neon, helium, krypton and xenon. Chemically, these gases are inert, dissolve in body fluids depending on the partial pressure, the absolute amount of these gases in the blood and body tissues is negligible.
3. An important component of atmospheric air is carbon dioxide (carbon dioxide, carbon dioxide,). In nature, carbon dioxide is found in free and bound states in the amount of 146 billion tons, of which only 1.8% of its total amount is contained in the atmospheric air. Its bulk (up to 70%) is in a dissolved state in the water of the seas and oceans. Some mineral compounds, limestones and dolomites contain about 22% of the total amount of dioxide and carbon. The rest is accounted for by animals and vegetable world, coal, oil and humus.
Under natural conditions, there are continuous processes of emission and absorption of carbon dioxide. It is released into the atmosphere due to the respiration of humans and animals, combustion processes, decay and fermentation, during the industrial burning of limestone and dolomite, etc. At the same time in nature there are processes of assimilation of carbon dioxide, which is absorbed by plants in the process of photosynthesis.
Carbon dioxide plays an important role in the life of animals and humans, being a physiological agent of the respiratory center.
When high concentrations of carbon dioxide are inhaled, the redox processes in the body are disrupted. With an increase in its content in the inhaled air up to 4%, headaches, tinnitus, palpitations, agitated state are noted; at 8% death occurs.
From a hygienic point of view, the content of carbon dioxide is an important indicator by which to judge the degree of air purity in residential and public buildings. The accumulation of large quantities of it in the indoor air indicates a sanitary problem (crowding, poor ventilation).
IN normal conditions with natural ventilation of the room and infiltration of outside air through the pores building materials the content of carbon dioxide in the air of residential premises does not exceed 0.2%. With an increase in its concentration in the room, a deterioration in the well-being of a person, a decrease in performance can be noted. This is due to the fact that simultaneously with an increase in the amount of carbon dioxide in the air of residential and public buildings, other properties of the air deteriorate: its temperature and humidity increase, gaseous products of human activity, the so-called anthropotoxins (mercaptan, indole, hydrogen sulfide, ammonia) appear.
With an increase in the content of CO 2 in the air and deterioration of meteorological conditions in residential and public buildings, there is a change in the ionization regime of the air (an increase in the number of heavy ions and a decrease in the number of light ions), which is explained by the absorption of light ions during respiration and contact with the skin, as well as the intake of heavy ions. with exhaled air.
The maximum permissible concentration of carbon dioxide in the air of medical institutions should be considered 0.07%, in the air of residential and public buildings - 0.1%. The latter value is taken as a calculated value when determining the ventilation efficiency in residential and public buildings.
4. In addition to the main components, atmospheric air contains gases released as a result of natural processes occurring on the Earth's surface and in the atmosphere.
Hydrogencontained in the air in the amount of 0.00005%. It is formed in the high layers of the atmosphere due to the photochemical decomposition of water molecules into oxygen and hydrogen. Hydrogen does not support respiration; in a free state, it is not assimilated or released by biological objects. In addition to hydrogen, the atmospheric air contains a small amount of methane; usually the concentration of methane in the air does not exceed 0, 00022%. Methane is released during anaerobic decay of organic compounds. how component is part of natural gas and gas oil wells. Inhalation of air containing methane in high concentrations may cause death from asphyxiation.
As a decomposition product organic matter there are small amounts in the atmospheric air ammonia. Its concentration depends on the degree of pollution of a given territory with sewage and organic emissions. In winter, due to the slowing down of decay processes, the concentration of ammonia is slightly lower than in summer. During anaerobic decomposition of sulfur-containing organic substances, the formation of hydrogen sulfide, which, even in small concentrations, gives the air bad smell... In the atmospheric air, iodine and hydrogen peroxide can be found in small concentrations. Iodine gets into the atmospheric air due to the presence of the smallest droplets of sea water and seaweed. Due to the interaction of UV rays with air molecules, hydrogen peroxide; together with ozone, it promotes the oxidation of organic matter in the atmosphere.
In the atmospheric air are suspended solids, which are represented by dust of natural and artificial origin. The composition of natural dust includes space, volcanic, terrestrial, sea dust and dust formed during forest fires.
Natural processes play an important role in freeing the atmosphere from suspended solids self-cleaning, among which the dilution of pollution by convection air currents at the Earth's surface is of great importance. An essential element of self-cleaning of the atmosphere is the fallout of large particles of dust and soot from the air (sedimentation). With the rise to the height, the amount of dust decreases; dust of terrestrial origin is absent at an altitude of 7 - 8 km from the Earth's surface. A significant atmospheric precipitation plays a role in self-cleaning processes, increasing the amount of settled soot and dust. The dust content in the atmospheric air is influenced by meteorological conditions and aerosol dispersion. Coarse dust with a particle diameter of more than 10 microns quickly falls out, fine dust with a particle diameter of less than 0.1 microns practically does not fall out and is in suspension.
Given in table. 1.1 the composition of atmospheric air undergoes various changes in closed rooms. Firstly, the percentage of individual mandatory components changes, and, secondly, additional impurities that are not characteristic of clean air appear. In this paragraph, we will talk about changes in the gas composition and its permissible deviations from normal.
The most important gases for human life are oxygen and carbon dioxide, which are involved in gas exchange between humans and the environment. This gas exchange occurs mainly in the human lungs during breathing. Gas exchange through the skin surface is about 100 times less than through the lungs, since the surface of the adult human body is approximately 1.75 m2, and the surface of the lung alveoli is approximately 200 m2. The respiration process is accompanied by the formation of heat in the human body in an amount from 4.69 to 5.047 (on average 4.879) kcal per 1 liter of absorbed oxygen (converted into carbon dioxide). It should be noted that only a small part of the oxygen contained in the inhaled air is absorbed (approximately 20%). So, if the atmospheric air contains about 21% of oxygen, then in the air exhaled by a person it will be about 17%. Usually the amount of carbon dioxide exhaled is less than the amount of oxygen absorbed. The ratio of the volumes of carbon dioxide emitted by a person and absorbed oxygen is called the respiratory coefficient (RR), which usually ranges from 0.71 to 1. However, if a person is in a state of strong excitement or does very hard work, the RR may even be greater than unity.
The amount of oxygen a person needs to maintain normal life depends mainly on the intensity of the work he does and is determined by the degree of nervous and muscular tension. Blood oxygen uptake occurs best at a partial pressure of about 160 mm Hg. Art. that at atmospheric pressure 760 mmHg Art. corresponds to the normal percentage of oxygen in atmospheric air, i.e. 21%.
Due to the ability of the human body to adapt, normal breathing can be observed even with lower amounts of oxygen.
If the reduction in the oxygen content in the air occurs due to inert gases (for example, nitrogen), then a significant decrease in the amount of oxygen is possible - up to 12%.
However, in closed rooms, a decrease in the oxygen content is accompanied not by an increase in the concentration of inert gases, but by the accumulation of carbon dioxide. Under these conditions, the maximum permissible minimum oxygen content in the air should be much higher. Usually the oxygen content of 17% by volume is taken as the norm for this concentration. Generally speaking, in closed rooms, the percentage of oxygen never drops to this level, since the concentration of carbon dioxide reaches the limit value much earlier. Therefore, in practice, it is more important to establish maximum permissible norms for the content of not oxygen, but carbon dioxide in closed rooms.
Carbon dioxide CO2 is a colorless gas with a mild sour taste and odor; it is 1.52 times heavier than air, slightly poisonous. The accumulation of carbon dioxide in indoor air leads to headaches, dizziness, weakness, loss of sensitivity and even loss of consciousness.
It is believed that the amount of carbon dioxide in the atmospheric air is 0.03% by volume. This is true for rural areas... In the air of large industrial centers, its content is usually higher. For calculations, a concentration of 0.04% is taken. The air exhaled by humans contains approximately 4% carbon dioxide.
Without any harmful consequences for the human body, concentrations of carbon dioxide can be tolerated in indoor air, significantly higher than 0.04%.
The value of the maximum permissible concentration of carbon dioxide depends on the length of stay of people in a particular enclosed space and on their occupation. For example, for sealed shelters, when healthy people are accommodated in them for a period of no more than 8 hours, a norm of 2% can be adopted as the maximum permissible concentration of CO2. With a short stay of people, this rate can be increased. The ability of a person to stay in an environment with high concentrations of carbon dioxide is due to the ability of the human body to adapt to various conditions. When the concentration of CO2 is higher than 1%, a person begins to inhale much more air. So, at a CO2 concentration of 3%, respiration doubles even at rest, which in itself does not cause noticeable negative consequences when a person remains in such air for a relatively short time. If a person stays in a room with a CO2 concentration of 3% long enough (3 or more days), he is in danger of losing consciousness.
With a long stay of people in sealed rooms and when people perform a particular job, the maximum permissible concentration of carbon dioxide should be significantly less than 2%. It is allowed to fluctuate from 0.1 to 1%. The carbon dioxide content of 0.1% can be considered acceptable for ordinary unpressurized premises of buildings and structures for various purposes. A lower concentration of carbon dioxide (about 0.07-0.08) should be prescribed only for the premises of medical and children's institutions.
As will be clear from what follows, the requirements for the content of carbon dioxide in the indoor air of ground-based buildings are usually easily met if the sources of its emission are people. Otherwise, the question is when carbon dioxide accumulates in production facilities as a result of certain technological processesoccurring, for example, in yeast, brewing, hydrolysis plants. In this case, 0.5% is taken as the maximum permissible concentration of carbon dioxide.
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 quite constant and is determined by the following figures (Table 3).
These figures may fluctuate slightly depending on different 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, that is, 760 mm, and is 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 is explained by 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.
