The composition of the air in percent in the city. What percentage of oxygen is in the air. Basic elements of the atmosphere
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.
Let's make a reservation right away, nitrogen in the air occupies a large part, however, the chemical composition of the remaining share 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 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 to one funny fact: oxygen was discovered twice - in 1771 and 1774, however, due to the difference in the 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 related unpleasant symptoms. 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. A significant biological role of 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. 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 fighting, the food industry as a gas and as food supplement E290 - 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 lanterns, bright signs and modern headlights use the fifth most common chemical element, which is also inhaled by a person - 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 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 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 much greater quantities. 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 establishes 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 π 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 π 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 industries, 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 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 of helium), and more recently, inhalation of this gas has been added to the doping list.
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, atmospheric air contains argon, helium, neon, krypton, hydrogen, xenon and other gases. Small amounts of ozone, nitric oxide, iodine, methane, and water vapor are present in the atmospheric air.
In addition to the constant components of the atmosphere, it contains a variety of pollution introduced into the atmosphere by human production activities.
1. Important integral part atmospheric air is oxygen , the amount of which in the earth's atmosphere is 1.18 Γ 10 15 tons. A 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 the processes of combustion and oxidation, on the other hand, it enters the atmosphere due to the processes of plant photosynthesis. Land plants and phytoplankton of the oceans fully restore the natural loss of oxygen. With a drop in the partial pressure of oxygen, the phenomena of oxygen starvation can develop, which is observed when ascending to a height. The critical level is the partial pressure of oxygen below 110 mm Hg. Art. Reducing 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 are added to the neutral formula of oxygen, forming ozone . Simultaneously with the formation of ozone, its decay occurs. The general biological significance of ozone is great: it absorbs short-wave UV radiation, which has a detrimental effect on biological objects. At the same time, ozone absorbs infrared radiation coming from the Earth, and thus prevents excessive cooling of its surface. Ozone concentrations are unevenly distributed along the height. Its greatest amount is observed at a level of 20-30 km from the Earth's surface.
2. Nitrogen in terms of quantitative content, it is the most significant component of atmospheric air; it belongs to inert gases. Life is impossible in a nitrogen atmosphere. Air nitrogen is assimilated by certain types of soil bacteria (nitrogen-fixing bacteria), as well as by 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 of it is formed during the decomposition of organic compounds. Thus, in nature there is a continuous circulation, as a result of which the nitrogen of the atmosphere is converted into organic compounds, restored and enters the atmosphere, then is again bound by biological objects.
Nitrogen is necessary as an oxygen diluent, since breathing pure oxygen leads to irreversible changes in the body.
However, an increased content of nitrogen 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, the inert gases of air include argon, neon, helium, krypton and xenon. Chemically, these gases are inert, they dissolve in body fluids depending on the partial pressure, the absolute amount of these gases in the blood and tissues of the body is negligible.
3. An important component of atmospheric air is carbon dioxide (carbon dioxide, carbonic acid). In nature, carbon dioxide is in free and bound states in the amount of 146 billion tons, of which only 1.8% of its total amount is contained in atmospheric air. Most of it (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 for animals and vegetable world, coal, oil and humus.
Under natural conditions, there are continuous processes of release and absorption of carbon dioxide. It is released into the atmosphere due to the respiration of humans and animals, the processes of combustion, decay and fermentation, during industrial roasting of limestones and dolomites, etc. At the same time, processes of assimilation of carbon dioxide are going on in nature, 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 causative agent of the respiratory center.
When high concentrations of carbon dioxide are inhaled, the redox processes in the body are disturbed. With an increase in its content in the inhaled air up to 4%, headaches, tinnitus, palpitations, and an excited state are noted; at 8% death occurs.
From a hygienic point of view, the content of carbon dioxide is an important indicator by which the degree of air purity in residential and public buildings is judged. The accumulation of large amounts of it in indoor air indicates sanitary problems (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 working capacity, may be noted. This is explained by 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 vital activity appear, the so-called anthropotoxins (mercaptan, indole, hydrogen sulfide, ammonia).
With an increase in the content of CO 2 in the air and the deterioration of meteorological conditions in residential and public buildings, the ionization regime of the air changes (an increase in the number of heavy and a decrease in the number of light ions), which is explained by the absorption of light ions during breathing and contact with the skin, as well as the intake of heavy ions with exhaled air.
The maximum allowable 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 one when determining the efficiency of ventilation 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 surface of the Earth and in the atmosphere.
Hydrogen contained in the air in an 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 absorbed and is not released by biological objects. In addition to hydrogen, 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 oil well gas. When inhaling air containing methane in high concentrations, death from asphyxia is possible.
Like a decomposition product organic matter small amounts are present in the air ammonia. Its concentrations depend on the degree of contamination of the area with sewage and organic emissions. In winter, due to the slowdown in the processes of decay, the concentration of ammonia is slightly lower than in summer. During anaerobic processes of decomposition of sulfur-containing organic substances, the formation of hydrogen sulfide, which already in small concentrations gives the air bad smell. In atmospheric air, iodine and hydrogen peroxide can be found in small concentrations. Iodine enters the atmospheric air due to the presence of tiny droplets sea ββwater and seaweed. Due to the interaction of UV rays with air molecules, hydrogen peroxide; together with ozone, it contributes to the oxidation of organic substances in the atmosphere.
In the atmospheric air are suspended matter, which are represented by dust of natural and artificial origin. The composition of natural dust includes cosmic, volcanic, ground, sea dust and dust generated during forest fires.
Natural processes play an important role in the release of the atmosphere from suspended solids. self-cleaning, among which the dilution of pollution by convection air currents near the Earth's surface is of significant importance. An essential element of self-purification of the atmosphere is the precipitation of large particles of dust and soot from the air (sedimentation). As the altitude increases, the amount of dust decreases; at a height of 7 - 8 km from the Earth's surface, there is no dust of terrestrial origin. Significant Precipitation plays a role in self-cleaning processes, increasing the amount of settled soot and dust. The dust content in the atmospheric air is affected by meteorological conditions and aerosol dispersion. Coarse dust with a particle diameter of more than 10 microns falls out quickly, 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 enclosed spaces. Firstly, the percentage of certain essential components changes, and, secondly, additional impurities appear that are not characteristic of pure air. In this paragraph, we will discuss 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 the gas exchange of a person with the environment. This gas exchange takes place mainly in the human lungs during respiration. Gas exchange occurring through the surface of the skin is about 100 times less than through the lungs, since the surface of the body of an adult is approximately 1.75 m2, and the surface of the alveoli of the lungs is about 200 m2. The process of respiration is accompanied by the formation of heat in the human body in an amount of 4.69 to 5.047 (on average 4.879) kcal per 1 liter of absorbed oxygen (passed into carbon dioxide). It should be noted that only a small part of the oxygen contained in the inhaled air (approximately 20%) is absorbed. So, if in the atmospheric air there is approximately 21% of oxygen, then in the air exhaled by a person it will be about 17%. Typically, the amount of carbon dioxide exhaled is less than the amount of oxygen taken in. The ratio of the volumes of carbon dioxide emitted by a person and the oxygen absorbed is called the respiratory coefficient (RC), which usually ranges from 0.71 to 1. However, if a person is in a state of high excitement or performs very hard work, the DC can be even greater than one.
The amount of oxygen necessary for a person to maintain normal life activity mainly depends on the intensity of the work performed by him and is determined by the degree of nervous and muscular tension. Assimilation of oxygen by the blood 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 the atmospheric air, i.e. 21%.
Due to the ability of the human body to adapt, normal breathing can be observed even with smaller 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 enclosed spaces, 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 allowable minimum oxygen content in the air should be much higher. Usually, the oxygen content equal to 17% by volume is taken as the norm for this concentration. Generally speaking, indoors, the percentage of oxygen never drops to this level, since the concentration of carbon dioxide reaches the limit value much earlier. Therefore, it is practically more important to set the limit allowable norms content in enclosed spaces is not oxygen, but carbon dioxide.
Carbon dioxide CO2 is a colorless gas with a slight sour taste and smell; 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 sensation and even loss of consciousness.
It is believed that in atmospheric air the amount of carbon dioxide 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 a person contains about 4% carbon dioxide.
Without any harmful consequences for the human body, concentrations of carbon dioxide much higher than 0.04% can be tolerated in indoor air.
The value of the maximum allowable concentration of carbon dioxide depends on the length of stay of people in a particular enclosed space and on the type of their occupation. For example, for sealed shelters, when healthy people are placed in them for a period of not more than 8 hours, a norm of 2% can be taken as the maximum allowable concentration of CO2. With a short stay of people, this rate can be increased. The possibility of a person being in an environment with high concentrations of carbon dioxide is due to the ability human body adapt to different conditions. At a concentration of CO2 higher than 1%, a person begins to inhale significantly more air. So, at a CO2 concentration of 3%, breathing doubles even at rest, which in itself does not cause noticeable negative consequences during a relatively short stay in such air of a person. If a person stays in a room with a CO2 concentration of 3% for a sufficiently long time (3 or more days), he is threatened with loss of consciousness.
When people stay in sealed rooms for a long time and when people perform one or another work, the value of the maximum allowable concentration of carbon dioxide should be significantly less than 2%. It can fluctuate from 0.1 to 1%. A carbon dioxide content of 0.1% can also be considered acceptable for ordinary non-pressurized premises of buildings and structures for various purposes. A lower concentration of carbon dioxide (of the order of 0.07-0.08) should be prescribed only for the premises of medical and children's institutions.
As will be clear from the following, the requirements for the content of carbon dioxide in the air of the premises of ground buildings are usually easily met if the sources of its release are people. Otherwise, the question is when carbon dioxide accumulates in industrial premises as a result of some technological processes occurring, for example, in yeast, breweries, hydrolysis shops. In this case, 0.5% is taken as the maximum allowable concentration of carbon dioxide.
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%. The partial pressure of atmospheric oxygen 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 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 and the blood capillaries of the lungs play an active role, through which the passage of gases occurs.
