Air is a natural mixture of gases

At the word "air" most of us involuntarily come to mind, perhaps a somewhat naive comparison: air is what we breathe. Indeed, the etymological dictionary of the Russian language indicates that the word "air" is borrowed from the Church Slavonic language: "sigh". From a biological point of view, air is therefore the medium for sustaining life through oxygen. The air might not contain oxygen - life would still develop in anaerobic forms. But the complete absence of air, apparently, excludes the possibility of the existence of any organisms.

For physicists, air is primarily the earth's atmosphere and the gaseous envelope that surrounds the earth.

And what does the air itself represent from the point of view of chemistry?

Scientists took a lot of effort, work and patience to reveal this mystery of nature, that air is not an independent substance, as it was believed more than 200 years ago, but is a complex mixture of gases. For the first time, the scientist - artist Leonardo da Vinci (15th century) spoke about the complex composition of the air.

About 4 billion years ago, Earth's atmosphere was composed primarily of carbon dioxide. Gradually, it dissolved in water, reacted with rocks, forming calcium and magnesium carbonates and bicarbonates. With the advent of green plants, this process began to proceed much faster. By the time man appeared, carbon dioxide, so necessary for plants, had already become a deficit. Its concentration in air before the industrial revolution was only 0.029%. Over the course of 1.5 billion years, the oxygen content gradually increased.

The chemical composition of the air

The quantitative composition of the air was first established by the French scientist Antoine Laurent Lavoisier. Based on the results of his famous 12-day experiment, he concluded that all air as a whole consists of oxygen suitable for breathing and combustion, and nitrogen, a lifeless gas, in proportions of 1/5 and 4/5 of the volume, respectively. He heated metallic mercury in a retort on a brazier for 12 days. The end of the retort was brought under a bell placed in a vessel with mercury. As a result, the level of mercury in the bell rose by about 1/5. An orange substance - mercury oxide - was formed on the surface of the mercury in the retort. The gas remaining under the bell was not breathable. The scientist proposed to rename the "vital air" to "oxygen", because when burned in oxygen, most of the substances are converted into acids, and "suffocating air" - into "nitrogen", tk. it does not support life, it hurts life.

Lavoisier's experience

The main constituent of air for us is oxygen, it is 21% in the air by volume. Oxygen is diluted with a large amount of nitrogen - 78% of the volume of air and a relatively small volume of noble inert gases - about 1%. Variable components are also part of the air - carbon monoxide (IV) or carbon dioxide and water vapor, the amount of which depends on various reasons. These substances enter the atmosphere naturally. During volcanic eruptions, sulfur dioxide, hydrogen sulfide and elemental sulfur are released into the atmosphere. Dust storms create dust in the air. Nitrogen oxides are released into the atmosphere during lightning electrical discharges, during which nitrogen and oxygen in the air react with each other, or as a result of the activity of soil bacteria capable of releasing nitrogen oxides from nitrates; forest fires and burning of peat bogs also contribute to this. The processes of destruction of organic substances are accompanied by the formation of various gaseous sulfur compounds. The water in the air determines its moisture content. Other substances have a negative role: they pollute the atmosphere. For example, there is a lot of carbon dioxide in the air of cities devoid of greenery, water vapor - above the surface of the oceans and seas. The air contains small amounts of sulfur (IV) oxide or sulfur dioxide, ammonia, methane, nitric oxide (I) or nitrous oxide, hydrogen. The air is especially saturated with them near industrial enterprises, gas and oil fields or volcanoes. There is another gas in the upper atmosphere - ozone. A variety of dust flies in the air, which we can easily notice when looking from the side at a thin beam of light falling from behind a curtain into a darkened room.

Constant constituents of air gases:

· Oxygen

· Nitrogen

· Inert gases

Variable constituents of air gases:

· Carbon monoxide (IV)

· Ozone

· Other

Conclusion.

1. Air is a natural mixture of gaseous substances, in which each substance has and retains its physical and chemical properties, so the air can be separated.

2. Air is a colorless gaseous solution, density - 1.293 g / l, at temperatures of -190 0 С it turns into a liquid state. Liquid air is a bluish liquid.

3. Living organisms are closely related to air substances, which have a certain effect on them. And at the same time, living organisms affect it, since they perform certain functions: redox - they oxidize, for example, carbohydrates to carbon dioxide and reduce it to carbohydrates; gas - absorb and emit gases.

Thus, living organisms created in the past and maintain the atmosphere of our planet for millions of years.

Air pollution - the introduction of new uncharacteristic physical, chemical and biological substances into the atmospheric air or a change in the natural average long-term concentration of these substances in it.

In the process of photosynthesis, carbon dioxide is removed from the atmosphere, and returns in the processes of respiration and decay. The balance established in the course of the evolution of the planet between these two gases began to be disturbed, especially in the second half of the 20th century, when the influence of man on nature began to increase. So far, nature is coping with disturbances of this balance thanks to the water of the ocean and its algae. But how long will nature have enough strength?

Scheme. Air pollution

Main air pollutants in Russia

The number of cars is constantly growing, especially in large cities, respectively, the emission of harmful substances into the air is growing. 60% of the emissions of harmful substances in the city are "on the conscience" of cars!
Thermal power enterprises in Russia emit up to 30% of pollutants into the atmosphere, and another 30% is the contribution of industry (ferrous and non-ferrous metallurgy, oil production and oil refining, the chemical industry and the production of building materials). The level of air pollution from natural sources is background ( 31–41% ), it changes little over time ( 59–69% ). At present, the problem of anthropogenic pollution of the atmosphere has acquired a global character. What kind of pollutants, dangerous for all living things, enter the atmosphere? These are cadmium, lead, mercury, arsenic, copper, soot, mercaptans, phenol, chlorine, sulfuric and nitric acids and other substances. We will study some of these substances in the future, learn their physical and chemical properties and talk about the destructive power hidden in them for our health.

The scale of environmental pollution of the planet, Russia

In which countries of the world is the air most polluted by transport exhaust gases?
The greatest danger of atmospheric pollution from exhaust gases threatens countries with a powerful fleet of vehicles. For example, in the United States, motor vehicles account for about 1/2 of all harmful emissions into the atmosphere (up to 50 million tons annually). The vehicle fleet in Western Europe annually emits up to 70 million tons of harmful substances into the air, and in Germany, for example, 30 million cars account for 70% of the total volume of harmful emissions. In Russia, the situation is aggravated by the fact that the vehicles in operation comply with environmental standards only by 14.5%.
It pollutes the atmosphere and air transport with exhaust plumes from many thousands of aircraft. According to expert estimates, as a result of the activities of the global vehicle fleet (and this is about 500 million engines), 4.5 billion tons of carbon dioxide alone enter the atmosphere annually.
Why are these pollutants dangerous? Heavy metals - lead, cadmium, mercury - have a harmful effect on the human nervous system, carbon monoxide - on the blood composition; sulfur dioxide, interacting with the water of rain and snow, turns into acid and causes acid rain. What is the scale of this pollution? The main regions where acid rain is spread are the USA, Western Europe, and Russia. Recently, these include the industrial regions of Japan, China, Brazil, India. The spread of acid precipitation is associated with the concept of transboundary - the distance between the regions of their formation and the regions of fallout can be hundreds and even thousands of kilometers. For example, the main culprit for acid rain in southern Scandinavia is the industrial regions of Great Britain, Belgium, the Netherlands and Germany. Acid rain is transported to the Canadian provinces of Ontario and Quebec from neighboring regions of the United States. These precipitations are transported to the territory of Russia from Europe by westerly winds.
An unfavorable ecological situation has developed in the northeast of China, in the Pacific belt of Japan, in the cities of Mexico City, Sao Paulo, and Buenos Aires. In Russia in 1993, in 231 cities with a total population of 64 million people, the content of harmful substances in the air exceeded the norm. In 86 cities, 40 million people live in conditions where pollution exceeds the norms by 10 times. Among these cities are Bryansk, Cherepovets, Saratov, Ufa, Chelyabinsk, Omsk, Novosibirsk, Kemerovo, Novokuznetsk, Norilsk, Rostov. In terms of the amount of harmful emissions, the Ural region occupies the first place in Russia. So, in the Sverdlovsk region, the state of the atmosphere does not meet the standards in 20 territories, where 60% of the population lives. In the city of Karabash, Chelyabinsk Region, a copper smelter annually emits 9 tons of harmful compounds into the atmosphere for each inhabitant. The incidence of cancer here is 338 cases per 10 thousand inhabitants.
An alarming situation has also developed in the Volga region, in the south of Western Siberia, and in Central Russia. In Ulyanovsk, more than the Russian average, people suffer from diseases of the upper respiratory tract. The incidence of lung cancer has increased 20 times since 1970, the city has one of the highest infant mortality rates in Russia.
A large number of chemical enterprises are concentrated in the city of Dzerzhinsk in a limited area. Over the past 8 years, 60 emissions of potent toxic substances into the atmosphere have occurred here, leading to emergency situations, in some cases resulting in the death of people. In the Volga region, up to 300 thousand tons of soot, ash, soot, carbon oxides fall on city residents annually. Moscow ranks 15th among Russian cities in terms of the total level of air pollution.

The chemical composition of atmospheric air and its hygienic value.

The chemical composition of atmospheric air... Atmospheric air is a mixture of many gaseous substances. The bulk of the air is oxygen and nitrogen, in addition, it contains carbon dioxide, argon, neon, helium, and other gases. Oxygen O 2- the most important component of atmospheric air 20.95%. The human body is sensitive to a lack of oxygen. A decrease in its content in the air to 17% leads to an increase in heart rate and respiration. At an oxygen concentration of 11-13%, there is a pronounced oxygen deficiency, leading to a sharp decrease in performance. The content of 7-8% oxygen in the air is incompatible with life. Along with the processes of consumption, the reverse processes also continuously occur - the restoration of oxygen in the air due to the release of it by the green parts of plants, therefore, the oxygen content in the atmospheric air remains almost constant. The partial pressure of oxygen is important for the body, and not its absolute content in the inhaled air, since the transfer of oxygen from the alveolar air to the blood, and from it to the tissue, occurs under the influence of the difference in partial pressure. The oxygen partial pressure decreases with increasing terrain altitude. A drop in partial pressure in humans and animals causes the phenomenon of oxygen starvation (a decrease in blood oxygen saturation), while oxidative processes in the tissues are disrupted. General health worsens, rapid breathing is observed. Oxygen starvation is observed, for example, when climbing mountains, etc. Even an ascent to a height of 300m can cause mountain or altitude sickness. However, prolonged training or permanent residence in high-altitude areas makes the body less sensitive to lack of oxygen. A metered increase in the partial pressure of oxygen in the air in pressure chambers is used in surgery, therapy and emergency care. Oxygen in its pure form has a toxic effect. So, in experiments on animals, it was shown that when breathing pure oxygen in animals, atelectasis in the lungs is found in 1-2 hours, after 3-6 hours - a violation of capillary permeability in the lungs, after 24 hours - the phenomenon of pulmonary edema. Used in medicine: in oxygen bags (40 - 60% About 2), in pressure chambers (hyperbaric oxygenation method).

Nitrogen N 2- the main component of atmospheric air, accounting for approximately 78% of its volume. Nitrogen belongs to inert gases, it does not support breathing and combustion. It plays an important biological role by participating in the cycle of nitrogenous substances. In addition, nitrogen serves as an oxygen diluent, since life in pure oxygen is impossible. At nitrogen concentrations exceeding the permissible (90-93%), death occurs. The most pronounced unfavorable properties of nitrogen are manifested at elevated atmospheric pressure, which is associated with its narcotic effect and participation in the development of decompression sickness. Carbon dioxide CO 2, or carbon dioxide, is present in the atmospheric air in small quantities. The processes of vital activity of living organisms, the processes of combustion, decay, fermentation are accompanied by its release. However, despite the numerous sources of carbon dioxide formation, its significant increase in the atmospheric air does not occur. This is due to the fact that carbon dioxide is assimilated by plants, and carbon participates in the construction of organic matter, and oxygen enters the atmosphere again. In the air of industrial cities, the content of carbon dioxide is somewhat higher than in the air of the countryside, which is explained by its intake with the flue gases of industrial enterprises and communal facilities, with the exhaust gases of vehicles, etc. Carbon dioxide is a physiological causative agent of the respiratory center, therefore, an increase in its content (over 4%) causes increased breathing. In natural conditions, there are cases when carbon dioxide accumulates in large, even life-threatening concentrations, for example, in abandoned wells, mines, basements, etc. However, the usual concentrations of carbon dioxide in the ambient air are not hygienic. In hygienic terms, the content of carbon dioxide is an indicator by which the degree of air purity in residential and public buildings is judged. The maximum permissible concentration of carbon dioxide in residential and public buildings is 0.1%. High content ozone О 3 causes a number of optical phenomena (mirages), has a significant effect on the intensity and spectral composition of electromagnetic radiation. Ozone absorbs short-wave ultraviolet radiation, which is harmful to living organisms. Application in medicine: deodorization of air (destroys putrid odors), disinfection of air and water. TO inert gases contained in the atmospheric air include argon, neon, helium, krypton etc. Chemically, they are inert, and their dangerous effect on the body is associated with their radioactivity. Under natural conditions, they determine the natural radioactivity of the atmosphere, in those concentrations in which they are found in the atmosphere, they do not have an adverse effect on humans.

Air pollution- this is the formation of physicochemical compounds, agents or substances in it, due to both natural (natural) and artificial (anthropogenic) factors (Table 1). Table 1. Sources of air pollution

Among the immediate natural impurities atmospheric air - refers to ammonia, which enters the air as a result of the decomposition of nitrogenous organic substances. And hydrogen sulfide, which enters the air as a result of the decay of protein substances, which include sulfur, as well as water vapor and dust. Natural sources of air pollution are, first of all, volcanic emissions, forest and steppe fires, dust storms, sea storms and typhoons. Volcanic eruptions and forest fires lead to large-scale disasters. During volcanic eruptions, huge volumes of aerosols and external particles are emitted, which are carried by tropospheric and stratospheric winds and absorb part of the solar radiation. Features of the formation of the air in a large city. All air pollution can be divided into three types: 1. Solid (dust, soot, etc.). 2. Liquid (vapor). 3. Gaseous. Compounds of sulfur, nitrogen, phosphorus, halogens, phenols and formaldehyde are the most active from the point of view of chemical interaction with the components of the atmosphere and biosphere. According to approximate data, hundreds of millions of tons of sulfur oxides enter the atmosphere annually (from sulfur dioxide emitted into the air by energy systems, acids containing sulfur are formed, which then fall out of the atmosphere in the form of so-called acid rain), nitrogen, halogen derivatives and other compounds. The main sources of air pollution are energy, automobile and air transport, enterprises of ferrous and non-ferrous metallurgy, chemical and petrochemical industries. Air pollution has a direct impact on human health. The number of skin diseases, diseases of the mucous membranes of the respiratory tract and eyes, malignant neoplasms of the lungs is increasing, various chronic diseases are sharply exacerbated, etc. The growth of atmospheric pollution also reduces the overall resistance of the organism. Smoke and waste gases (especially sulfur dioxide) over industrial areas and large cities can lead to the formation of smog (toxic fog). Concentrations of pollutants such as sulfur oxides, airborne dust and carbon monoxide can quickly reach levels that are hazardous to human health and can lead to respiratory failure, irritation of mucous membranes, circulatory problems, and often death. They can be especially dangerous for young children, the elderly and sick people. The physical London smog catastrophe of 1952 killed 4,000 people in two weeks. In 1952, 150 people died in the Ruhr area as a result of heavy smog. There are two types of smog: winter (London) and summer (Los Angeles). The meteorological prerequisite for winter smog is windless calm weather (temperature inversion). At the same time, a layer of warmer air is located above the earth's layer of cold air (below 700 m), there is almost no air movement near the earth's surface (less than 3 m / s). Horizontal and vertical air exchange is difficult. Pollutants, which are usually distributed through tall chimneys in high layers of air and carried over long distances, in this case accumulate in the surface layer. Summer smog is called photochemical smog. In the presence of nitrogen oxides and hydrocarbons in the atmospheric air and intense solar radiation, photooxidants, mainly ozone, are formed. This type of smog is rare in Central Europe. Reducing pollutant emissions is the only way to prevent smog. Hygienic regulation of harmful substances in the atmospheric air. and legislatively established maximum permissible concentrations of polluting components in the air (MPC). MPC are concentrations that do not have a direct or indirect harmful and unpleasant effect on a person, do not reduce his ability to work, do not negatively affect his well-being and mood. Measures for the sanitary protection of atmospheric air are divided into legislative, technological, planning and sanitary-technical. Of particular importance are legislative measures defining the responsibility of various organizations for the protection of atmospheric air. At present, when solving issues of atmospheric air protection, they are guided by the Constitution of the Russian Federation, the Federal Laws "On the Sanitary and Epidemiological Well-Being of the Population" (No. 52-F3 1999) and "On the Protection of Atmospheric Air" (No. 96 F3 1999, as amended in 2010) ... Measures aimed at preventing the adverse effects of atmospheric air pollution on public health are regulated by SanPiN 2.1.6.1032-06 "Hygienic requirements for ensuring the quality of atmospheric air in populated areas." Into the group technological activities includes measures that can be carried out at the enterprise itself in order to reduce emissions and reduce the concentration of dust and gases in the air (so-called waste-free technologies, automation and sealing of production facilities, etc.). Sanitary measures associated with the use of cleaning devices. These are dust, ash, gas catchers, dust chambers, filters, humidifying cleaning technologies, electrofiltration, etc. The device of high pipes (100m and more) contributes to a more intensive dispersion of gases. Correct calculation and justification of the pipe height are essential in protecting the surface layers of the atmosphere from pollution. Planning activities are based on on the principle of functional zoning of settlements (allocation of industrial and residential areas, wind rose accounting, etc.). This makes it possible to concentrate hazardous enterprises, taking into account aeroclimatic conditions and to justify the arrangement of mandatory gaps between enterprises and residential buildings (sanitary protection zones), as well as landscaping, road improvement, etc. Monitoring- continuous monitoring of environmental factors (air, water, etc.), MPC control.

How fresh the winter air is to breathe. How easy and pleasant it is to breathe deeply in the forest, near the sea or in the mountains. It is in such places that we strive to spend our weekend or another vacation. But the percentage of air in the heavenly corners of our planet is the same as in the cities where we live. So what's the deal? Why don't we feel the same clean air at home, far from dreaming forests, mountains and seas? Let's talk about the percentage of air composition and its quality.

21% oxygen (O2), 0.03% carbon dioxide (CO2), the rest is 79% nitrogen (N2) and negligible impurities.

As one of my school teachers used to say, "The dog is buried in impurities." The fact is that over the past 150 years, a huge amount of arsenic, cobalt, silicon, oxides of sulfur, nitrogen, carbon and other impurities harmful to health have entered the atmosphere.

Obviously, the concentration of these impurities in the air in rural areas is much lower than in cities and towns. And all, first of all, because of vehicles, which fogs everything around with their exhausts. The degree of pollution of precious air is determined mainly by geographic conditions.

This is the composition of the air as a percentage, friends. Obviously, a person should think about its quality and not pollute the atmosphere. Next, we will discuss some interesting facts.

Why does it get bad in a stuffy room?

A person inhales air, and exhales carbon dioxide and something else in the form of gaseous substances - this is how we were taught at school. We also studied the composition of the air there. Remember the time when you, for no reason at all, felt bad indoors (if such was the case). What do you think, because of what? You will be right if you assume that this room has not been ventilated for a long time.

You felt unwell because of the high concentration of all the same gaseous substances that you, along with the people around you, breathed in. The mixture exhaled by a person contains no more than 16-18 percent oxygen and 4-6 percent carbon dioxide. And this is 130-200 times more than in the air you breathe.

There are also other bad connections there. So the advice to regularly ventilate your homes and offices should not seem out of place. You will be healthier. Since then, he is responsible for their cleanliness and order.

Natural air purification

In the summer we sweep and water the asphalt of the streets in order not to breathe fine dust particles. But in winter, the composition of the air is cleaner, if only because this very dust and dirt hangs under the snow drifts.

Trees, so intensively planted in settlements, act as filters, cleaning the atmosphere from excess carbon dioxide. So they change the composition of the air for our good. Green plants absorb it and oxygenate the city air. Everyone in the same schools taught us that this process is called photosynthesis.

5 thousand cubic meters of air is purified by one tree, and a small park frees us from 200 tons of dust. That is, the more greenery is planted on the Earth, the better the air we breathe will be. It is not for nothing that plants are called the lungs of this planet.

Have you ever heard of ionization? So, a high concentration of negatively charged particles (ions) in the air has a beneficial effect on our organisms. Mountain seaside resorts and pine forests are famous for highly ionized air.

Also, if you are lucky enough to live near a waterfall or a fast-flowing mountain river, then air ions will give you good health.

The healing climate of such places does its job. Therefore, people living in these areas or nearby are less likely to get sick and are famous for their longevity. And yes, I almost forgot, to the required level. Especially in the winter. Breathe deliciously, friends!

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Denis Statsenko was with you. See you later

Less than 200 years ago, the earth's atmosphere contained 40% oxygen. Today, the air contains only 21% oxygen.

In the city park 20,8%

In the woods 21,6%

By the sea 21,9%

In the apartment and office less 20%

Scientists have shown that a 1% decrease in oxygen leads to a 30% decrease in performance.

Oxygen deficiency is a result of cars, industrial emissions and pollution. In the city, oxygen is 1% less than in the forest.

But the biggest culprit in the lack of oxygen is ourselves. Having built warm and sealed houses, living in apartments with plastic windows, we protected ourselves from fresh air. With each exhalation, reducing the concentration of oxygen and increasing the amount of carbon dioxide. Often, the oxygen content in the office is 18%, in the apartment 19%.

The air quality necessary to support the life processes of all living organisms on Earth,

is determined by its oxygen content.

Dependence of air quality on the percentage of oxygen in it.

Comfortable oxygen level in the air

Zone 3-4: limited by the legally approved standard for the minimum oxygen content in indoor air (20.5%) and the "standard" for fresh air (21%). For urban air, the oxygen content of 20.8% is considered normal.

Favorable oxygen level in the air

Zone 1-2: this level of oxygen is typical for ecologically clean areas, forests. The oxygen content in the air on the ocean coast can reach 21.9%

Insufficient oxygen content in the air

Zano 5-6: limited by the minimum permissible oxygen level when a person can be without a breathing apparatus (18%).

A person's stay in rooms with such air is accompanied by rapid fatigue, drowsiness, decreased mental activity, and headaches.

Prolonged exposure to such an atmosphere is hazardous to health.

Dangerously low oxygen levels in the air

Zone 7 and beyond: with oxygen content16% dizziness, rapid breathing,13% - loss of consciousness,12% - irreversible changes in the functioning of the body, 7% - death.

External signs of oxygen starvation (hypoxia)

- deterioration in skin color

- rapid fatigability, decreased mental, physical and sexual activity

- depression, irritability, sleep disturbance

- headaches

Prolonged exposure to an oxygen deficient room can lead to more serious health problems. oxygen is responsible for all metabolic processes of the body, then the consequence of its lack is:

Metabolic disease

Decreased immunity

A properly organized ventilation system for living and working premises can be the key to good health.

The role of oxygen for human health. Oxygen:

Increases mental performance;

Increases the body's resistance to stress and increased nervous stress;

Supports blood oxygen levels;

Improves the consistency of the work of internal organs;

Increases immunity;

Promotes weight loss. Regular oxygen consumption, combined with physical activity, leads to active breakdown of fats;

Sleep is normalized: it becomes deeper and longer, the period of falling asleep and physical activity decreases

Conclusions:

Oxygen influences our life, and the more it is, the more colorful and varied our life is.

You can buy an oxygen cylinder or drop everything and go to live in the forest. If this is not available to you, ventilate your apartment and office every hour. Drafts, dust, noise interfere, install ventilation that will supply you with fresh air and clean you from exhaust gases.

Do everything to keep fresh air in your home and you will see changes in your life.

The lower atmosphere is made up of a mixture of gases called air , in which liquid and solid particles are in suspension. 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. At the earth's surface, 99% of dry air consists of nitrogen (78% by volume or 76% by mass) and oxygen (21% by volume or 23% by mass). The remaining 1% is almost entirely argon. Only 0.08% remains for carbon dioxide CO2. Numerous other gases are included in 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

Composition of dry atmospheric air near the Earth's surface

The percentage of dry air near the earth's surface is very constant and almost the same everywhere. Only the carbon dioxide content can change significantly. As a result of the processes of respiration and combustion, 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 real atmosphere contains three important variables - water vapor, ozone and carbon dioxide. The content of water vapor in the air varies considerably, unlike other air constituents: at the earth's surface it fluctuates between hundredths of a percent and several percent (from 0.2% at polar latitudes to 2.5% at the equator, and in some cases ranges from almost zero to 4%). This is due to 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.

The atmosphere can be saturated. In this state, water vapor is contained in the air in an amount that is 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 excessive and condenses, turns into 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, enlarging, 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 with its transitions from a gaseous state to a liquid and solid. 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 the long-wave infrared radiation that the earth's surface emits. 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 of the lower air layers.

Large amounts of heat are spent on evaporation of water from the earth's surface, and when water vapor condenses in the atmosphere, this heat is released to the air. Condensation clouds reflect and absorb solar radiation as it travels 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 elasticity 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 elasticity of water vapor in a state of saturation is called saturation elasticity. This is the maximum water vapor pressure possible at a given temperature. For example, at a temperature of 0 °, the 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, you can determine how close the air is to saturation. To do this, calculate relative humidity. This is the name of the ratio of the actual elasticity e water vapor in air to saturation elasticity E at the same temperature, expressed as a percentage, i.e.

For example, at 20 ° C, the saturation elasticity is 23.4 mb. If the actual vapor pressure in the air is 11.7 mb, then the relative humidity is

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

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