The atmospheric air contains oxygen. The chemical composition of air and its hygienic significance

The lower layers of the atmosphere are made up of a mixture of gases called air. , in which liquid and solid particles are suspended. The total mass of the latter is insignificant in comparison with the entire mass of the atmosphere.

Atmospheric air is a mixture of gases, the main of which are nitrogen N2, oxygen O2, argon Ar, carbon dioxide CO2 and water vapor. Air without water vapor is called dry air. Near the earth's surface, dry air is 99% nitrogen (78% by volume or 76% by mass) and oxygen (21% by volume or 23% by mass). The remaining 1% falls almost entirely on argon. Only 0.08% remains for carbon dioxide CO2. Numerous other gases are part of the air in thousandths, millionths and even smaller fractions of a percent. These are krypton, xenon, neon, helium, hydrogen, ozone, iodine, radon, methane, ammonia, hydrogen peroxide, nitrous oxide, etc. The composition of dry atmospheric air near the Earth's surface is given in Table. one.

Table 1

The composition of dry atmospheric air near the Earth's surface

	Volume concentration, %	Molecular mass	Density in relation to density dry air
Oxygen (O2)
Carbon dioxide (CO2)
Krypton (Kr)
Hydrogen (H2)
Xenon (Xe)
dry air

The percentage composition of dry air near the earth's surface is very constant and practically the same everywhere. Only the content of carbon dioxide can change significantly. As a result of breathing and combustion processes, its volumetric content in the air of closed, poorly ventilated premises, as well as industrial centers, can increase several times - up to 0.1-0.2%. The percentage of nitrogen and oxygen changes quite insignificantly.

The composition of the real atmosphere includes three important variable components - water vapor, ozone and carbon dioxide. The content of water vapor in the air varies significantly, unlike other components of the air: at the earth's surface, it varies between hundredths of a percent and several percent (from 0.2% in polar latitudes to 2.5% at the equator, and in some cases fluctuates almost from zero to 4%). This is explained by the fact that, under the conditions existing in the atmosphere, water vapor can pass into a liquid and solid state and, conversely, can enter the atmosphere again due to evaporation from the earth's surface.

Water vapor continuously enters the atmosphere by evaporation from water surfaces, from moist soil and by transpiration of plants, while in different places and at different times it enters in different quantities. It spreads upward from the earth's surface, and is carried by air currents from one place on the Earth to another.

Saturation may occur in the atmosphere. In this state, water vapor is contained in the air in an amount that is the maximum possible at a given temperature. Water vapor is called saturating(or saturated), and the air containing it saturated.

The saturation state is usually reached when the air temperature drops. When this state is reached, then with a further decrease in temperature, part of the water vapor becomes redundant and condenses changes to a liquid or solid state. Water droplets and ice crystals of clouds and fogs appear in the air. Clouds can evaporate again; in other cases, droplets and crystals of clouds, becoming larger, can fall on the earth's surface in the form of precipitation. As a result of all this, the content of water vapor in each part of the atmosphere is constantly changing.

The most important weather processes and climate features are associated with water vapor in the air and its transitions from a gaseous state to a liquid and solid state. The presence of water vapor in the atmosphere significantly affects the thermal conditions of the atmosphere and the earth's surface. Water vapor strongly absorbs long-wave infrared radiation emitted by the earth's surface. In turn, he himself emits infrared radiation, most of which goes to the earth's surface. This reduces the nighttime cooling of the earth's surface and thus also the lower layers of the air.

Large amounts of heat are expended on the evaporation of water from the earth's surface, and when water vapor condenses in the atmosphere, this heat is transferred to the air. Clouds resulting from condensation reflect and absorb solar radiation on its way to the earth's surface. Precipitation from clouds is an essential element of weather and climate. Finally, the presence of water vapor in the atmosphere is essential for physiological processes.

Water vapor, like any gas, has elasticity (pressure). Water vapor pressure e proportional to its density (content per unit volume) and its absolute temperature. It is expressed in the same units as air pressure, i.e. either in millimeters of mercury, either in millibars.

The pressure of water vapor at saturation is called saturation elasticity. This is the maximum pressure of water vapor possible at a given temperature. For example, at a temperature of 0° saturation elasticity is 6.1 mb . For every 10° of temperature, the saturation elasticity approximately doubles.

If the air contains less water vapor than is needed to saturate it at a given temperature, it can be determined how close the air is to saturation. To do this, calculate relative humidity. This is the name of the ratio of actual elasticity e water vapor in the air to saturation elasticity E at the same temperature, expressed as a percentage, i.e.

For example, at a temperature of 20 °, the saturation elasticity is 23.4 mb. If, in this case, the actual vapor pressure in the air is 11.7 mb, then the relative humidity of the air is

The pressure of water vapor near the earth's surface varies from hundredths of a millibar (at very low temperatures in winter in Antarctica and Yakutia) to 35 mbi more (near the equator). The warmer the air, the more water vapor it can contain without saturation and, therefore, the greater the elasticity of water vapor can be in it.

Relative humidity can take on all values ​​- from zero for completely dry air ( e= 0) to 100% for saturation state (e = E).

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 amount 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 strong excitement or performs very hard work, the ROC 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., which at an atmospheric pressure of 760 mm Hg. 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 establish the maximum allowable norms for the content of not oxygen, but carbon dioxide in enclosed spaces.

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 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. At a concentration of CO2 higher than 1%, a person begins to inhale significantly more air. Thus, at a CO2 concentration of 3%, respiration 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.

With a long stay of people in sealed rooms 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. The question is different when carbon dioxide accumulates in industrial premises as a result of certain technological processes occurring, for example, in yeast, brewing, hydrolysis shops. In this case, 0.5% is taken as the maximum allowable concentration of carbon dioxide.

The chemical composition of the air

The air has the following chemical composition: nitrogen-78.08%, oxygen-20.94%, inert gases-0.94%, carbon dioxide-0.04%. These indicators in the surface layer can fluctuate within insignificant limits. Man basically needs oxygen, without which he cannot live, like other living organisms. But now it has been studied and proven that other constituents of the air are also of great importance.

Oxygen is a colorless and odorless gas, highly soluble in water. A person inhales approximately 2722 liters (25 kg) of oxygen per day at rest. Exhaled air contains about 16% oxygen. The nature of the intensity of oxidative processes in the body depends on the amount of oxygen consumed.

Nitrogen is a colorless and odorless gas, inactive, its concentration in the exhaled air almost does not change. It plays an important physiological role in creating atmospheric pressure, which is vital, and, together with inert gases, dilutes oxygen. With plant foods (especially legumes), nitrogen in a bound form enters the body of animals and participates in the formation of animal proteins, and, accordingly, the proteins of the human body.

Carbon dioxide is a colorless gas with a sour taste and a peculiar smell, highly soluble in water. The air exhaled from the lungs contains up to 4.7%. An increase in the carbon dioxide content of 3% in the inhaled air negatively affects the state of the body, there are sensations of compression of the head and headache, blood pressure rises, the pulse slows down, tinnitus appears, and mental arousal can be observed. With an increase in the concentration of carbon dioxide up to 10% in the inhaled air, loss of consciousness occurs, and then respiratory arrest may occur. Large concentrations quickly lead to paralysis of the brain centers and death.

The main chemical impurities that pollute the atmosphere are the following.

carbon monoxide(CO) - a colorless, odorless gas, the so-called "carbon monoxide". It is formed as a result of incomplete combustion of fossil fuels (coal, gas, oil) in conditions of lack of oxygen at low temperatures.

Carbon dioxide(CO 2), or carbon dioxide - a colorless gas with a sour smell and taste, a product of the complete oxidation of carbon. It is one of the greenhouse gases.

sulphur dioxide(SO 2) or sulfur dioxide is a colorless gas with a pungent odor. It is formed during the combustion of sulfur-containing fossil fuels, mainly coal, as well as during the processing of sulfur ores. It is involved in the formation of acid rain. Prolonged exposure to sulfur dioxide on a person leads to circulatory disorders and respiratory arrest.

nitrogen oxides(oxide and nitrogen dioxide). Formed during all combustion processes mostly in the form of nitrogen oxide. Nitric oxide quickly oxidizes to dioxide, which is a red-white gas with an unpleasant odor that strongly affects human mucous membranes. The higher the combustion temperature, the more intense the formation of nitrogen oxides.

Ozone- a gas with a characteristic odor, a stronger oxidizing agent than oxygen. It is considered one of the most toxic of all common air pollutants. In the lower atmospheric layer, ozone is formed as a result of photochemical processes involving nitrogen dioxide and volatile organic compounds (VOCs).

hydrocarbons- chemical compounds of carbon and hydrogen. These include thousands of different air pollutants found in unburned gasoline, dry cleaning fluids, industrial solvents, and more. Many hydrocarbons are dangerous in and of themselves. For example, benzene, one of the components of gasoline, can cause leukemia, and hexane can cause severe damage to the human nervous system. Butadiene is a strong carcinogen.

Lead- a silver-gray metal, toxic in any known form. Widely used in the production of solder, paint, ammunition, printing alloy, etc. Lead and its compounds, getting into the human body, reduce the activity of enzymes and disrupt the metabolism, in addition, they have the ability to accumulate in the human body. Lead compounds pose a particular threat to children, disrupting their mental development, growth, hearing, the child's speech, and his ability to concentrate.

Freons- a group of halogen-containing substances synthesized by man. Freons, which are chlorinated and fluorinated carbons (CFCs), as inexpensive and non-toxic gases, are widely used as refrigerants in refrigerators and air conditioners, foaming agents, in gas fire extinguishing installations, and the working fluid of aerosol packages (varnishes, deodorants).

industrial dust Depending on the mechanism of their formation, they are divided into the following classes:

mechanical dust - is formed as a result of grinding the product during the technological process,

sublimates - are formed as a result of volumetric condensation of vapors of substances during cooling of a gas passed through a process apparatus, installation or unit,

fly ash - the non-combustible fuel residue contained in the flue gas in suspension, is formed from its mineral impurities during combustion,

industrial soot - a solid highly dispersed carbon, which is part of an industrial emission, is formed during incomplete combustion or thermal decomposition of hydrocarbons.

The main parameter characterizing suspended particles is their size, which varies in a wide range - from 0.1 to 850 microns. The most dangerous particles are from 0.5 to 5 microns, since they do not settle in the respiratory tract and it is them that a person inhales.

Dioxins belong to the class of polychlorinated polycyclic compounds. Under this name, more than 200 substances are combined - dibenzodioxins and dibenzofurans. The main element of dioxins is chlorine, which in some cases can be replaced by bromine, in addition, dioxins contain oxygen, carbon and hydrogen.

Atmospheric air acts as a kind of mediator of pollution of all other objects of nature, contributing to the spread of large masses of pollution over considerable distances. Airborne industrial emissions (impurities) pollute the oceans, acidify soil and water, change the climate and destroy the ozone layer.

You can't touch it, you can't see it, and the main thing we owe him is life. Of course, this is the air that occupied not the last place in the folklore of every nation. How the people of antiquity imagined it, and what it really is - I will write about this below.

The gases that make up air

Natural mixture of gases called air. Its necessity and importance for the living can hardly be underestimated - it plays an important role in oxidative processes, which are accompanied by the release of energy necessary for all living things. Through experiments, scientists were able to determine its exact composition, but the main thing that needs to be understood is it is not a homogeneous substance, but a gas mixture. About 99% of the composition is a mixture of oxygen and nitrogen, and in general air forms the atmosphere our planet. So, the mixture consists of the following gases:

• methane;
• krypton;
• helium;
• xenon;
• hydrogen;
• neon;
• carbon dioxide;
• oxygen;
• nitrogen;
• argon.

It should be noted that composition is not constant and can vary significantly from site to site. For example, large cities are characterized by a high content of carbon dioxide. In the mountains will be observed reduced oxygen level, since this gas is heavier than nitrogen, and as it ascends, its density will decrease. Science Says Composition May Differ in Different Parts of the Planet 1% to 4% for each of the gases.

In addition to the percentage of gases, air is characterized by the following parameters:

• humidity;
• temperature;
• pressure.

Air is constantly in motion, forming vertical flows. Horizontal - winds that depend on certain natural conditions, therefore, they can have different characteristics of speed, strength and direction.

Air in folklore

Legends of every nation endow the air with some "living" qualities. As a rule, the spirits of this element were elusive and invisible creatures. According to legend, they inhabited mountain tops or clouds, and differed in predisposition to the person. They were the ones who thought created snowflakes and collected clouds into the clouds, flying across the sky on the winds.

The Egyptians considered air a symbol of life and the Indians believed that exhalation of Brahma - life, and inhalation, respectively - death. As for the Slavs, the air (wind) occupied almost a central place in the legends of this people. He could hear and sometimes even fulfill small requests. However, he was not always kind, sometimes speaking on the side of the forces of evil. in the form of an evil and unpredictable wanderer.

The atmosphere is the gaseous shell of our planet that rotates with the Earth. The gas in the atmosphere is called air. The atmosphere is in contact with the hydrosphere and partially covers the lithosphere. But it is difficult to determine the upper bounds. Conventionally, it is assumed that the atmosphere extends upwards for about three thousand kilometers. There it flows smoothly into the airless space.

The chemical composition of the Earth's atmosphere

The formation of the chemical composition of the atmosphere began about four billion years ago. Initially, the atmosphere consisted only of light gases - helium and hydrogen. According to scientists, the initial prerequisites for the creation of a gas shell around the Earth were volcanic eruptions, which, together with lava, emitted a huge amount of gases. Subsequently, gas exchange began with water spaces, with living organisms, with the products of their activity. The composition of the air gradually changed and in its present form was fixed several million years ago.

The main components of the atmosphere are nitrogen (about 79%) and oxygen (20%). The remaining percentage (1%) is accounted for by the following gases: argon, neon, helium, methane, carbon dioxide, hydrogen, krypton, xenon, ozone, ammonia, sulfur dioxide and nitrogen, nitrous oxide and carbon monoxide included in this one percent.

In addition, the air contains water vapor and particulate matter (plant pollen, dust, salt crystals, aerosol impurities).

Recently, scientists have noted not a qualitative, but a quantitative change in some air ingredients. And the reason for this is the person and his activity. Only in the last 100 years, the content of carbon dioxide has increased significantly! This is fraught with many problems, the most global of which is climate change.

Formation of weather and climate

The atmosphere plays a vital role in shaping the climate and weather on Earth. A lot depends on the amount of sunlight, on the nature of the underlying surface and atmospheric circulation.

Let's look at the factors in order.

1. The atmosphere transmits the heat of the sun's rays and absorbs harmful radiation. The ancient Greeks knew that the rays of the Sun fall on different parts of the Earth at different angles. The very word "climate" in translation from ancient Greek means "slope". So, at the equator, the sun's rays fall almost vertically, because it is very hot here. The closer to the poles, the greater the angle of inclination. And the temperature is dropping.

2. Due to the uneven heating of the Earth, air currents are formed in the atmosphere. They are classified according to their size. The smallest (tens and hundreds of meters) are local winds. This is followed by monsoons and trade winds, cyclones and anticyclones, planetary frontal zones.

All these air masses are constantly moving. Some of them are quite static. For example, the trade winds that blow from the subtropics towards the equator. The movement of others is largely dependent on atmospheric pressure.

3. Atmospheric pressure is another factor influencing climate formation. This is the air pressure on the earth's surface. As you know, air masses move from an area with high atmospheric pressure towards an area where this pressure is lower.

There are 7 zones in total. The equator is a low pressure zone. Further, on both sides of the equator up to the thirtieth latitudes - an area of ​​high pressure. From 30° to 60° - again low pressure. And from 60° to the poles - a zone of high pressure. Air masses circulate between these zones. Those that go from the sea to land bring rain and bad weather, and those that blow from the continents bring clear and dry weather. In places where air currents collide, atmospheric front zones are formed, which are characterized by precipitation and inclement, windy weather.

Scientists have proven that even a person's well-being depends on atmospheric pressure. According to international standards, normal atmospheric pressure is 760 mm Hg. column at 0°C. This figure is calculated for those areas of land that are almost flush with sea level. The pressure decreases with altitude. Therefore, for example, for St. Petersburg 760 mm Hg. - is the norm. But for Moscow, which is located higher, the normal pressure is 748 mm Hg.

The pressure changes not only vertically, but also horizontally. This is especially felt during the passage of cyclones.

The structure of the atmosphere

The atmosphere is like a layer cake. And each layer has its own characteristics.

. Troposphere is the layer closest to the Earth. The "thickness" of this layer changes as you move away from the equator. Above the equator, the layer extends upwards for 16-18 km, in temperate zones - for 10-12 km, at the poles - for 8-10 km.

It is here that 80% of the total mass of air and 90% of water vapor are contained. Clouds form here, cyclones and anticyclones arise. The air temperature depends on the altitude of the area. On average, it drops by 0.65°C for every 100 meters.

. tropopause- transitional layer of the atmosphere. Its height is from several hundred meters to 1-2 km. The air temperature in summer is higher than in winter. So, for example, over the poles in winter -65 ° C. And over the equator at any time of the year it is -70 ° C.

. Stratosphere- this is a layer, the upper boundary of which runs at an altitude of 50-55 kilometers. Turbulence is low here, water vapor content in the air is negligible. But a lot of ozone. Its maximum concentration is at an altitude of 20-25 km. In the stratosphere, the air temperature begins to rise and reaches +0.8 ° C. This is due to the fact that the ozone layer interacts with ultraviolet radiation.

. Stratopause- a low intermediate layer between the stratosphere and the mesosphere following it.

. Mesosphere- the upper boundary of this layer is 80-85 kilometers. Here complex photochemical processes involving free radicals take place. It is they who provide that gentle blue glow of our planet, which is seen from space.

Most comets and meteorites burn up in the mesosphere.

. mesopause- the next intermediate layer, the air temperature in which is at least -90 °.

. Thermosphere- the lower boundary begins at an altitude of 80 - 90 km, and the upper boundary of the layer passes approximately at the mark of 800 km. The air temperature is rising. It can vary from +500° C to +1000° C. During the day, temperature fluctuations amount to hundreds of degrees! But the air here is so rarefied that the understanding of the term "temperature" as we imagine it is not appropriate here.

. Ionosphere- unites mesosphere, mesopause and thermosphere. The air here consists mainly of oxygen and nitrogen molecules, as well as quasi-neutral plasma. The sun's rays, falling into the ionosphere, strongly ionize air molecules. In the lower layer (up to 90 km), the degree of ionization is low. The higher, the more ionization. So, at an altitude of 100-110 km, electrons are concentrated. This contributes to the reflection of short and medium radio waves.

The most important layer of the ionosphere is the upper one, which is located at an altitude of 150-400 km. Its peculiarity is that it reflects radio waves, and this contributes to the transmission of radio signals over long distances.

It is in the ionosphere that such a phenomenon as aurora occurs.

. Exosphere- consists of oxygen, helium and hydrogen atoms. The gas in this layer is very rarefied, and often hydrogen atoms escape into outer space. Therefore, this layer is called the "scattering zone".

The first scientist who suggested that our atmosphere has weight was the Italian E. Torricelli. Ostap Bender, for example, in the novel "The Golden Calf" lamented that each person was pressed by an air column weighing 14 kg! But the great strategist was a little mistaken. An adult person experiences pressure of 13-15 tons! But we do not feel this heaviness, because atmospheric pressure is balanced by the internal pressure of a person. The weight of our atmosphere is 5,300,000,000,000,000 tons. The figure is colossal, although it is only a millionth of the weight of our planet.