The percentage of nitrogen in the earth's atmosphere is. The composition and structure of the atmosphere. The role of nitrogen in the Earth's atmosphere

Why is there so much nitrogen in the Earth's atmosphere? and got the best answer

Answer from Marat[guru]
Several reasons can be identified. HOME: Earth is the only planet solar system, where the protein form of life was formed, stabilized and continues to develop. The composition of the Earth's primary atmosphere was simpler: hot water vapor and CO2, the main products of volcanic gases, predominated. After the atmosphere cooled, the processes of photosynthesis and water condensation led to a significant decrease in the proportion of CO2 and the appearance of free oxygen. IMPORTANT point: among the products of protein decomposition (animal and vegetable world) urea (carbamide) and uric acid play an important role. These substances, in turn, gradually undergo irreversible (!) hydrolysis with the formation of ammonia (NH3). IMPORTANT: NH3 is a lighter gas than a mixture of O2, CO2 and water vapor - therefore, it gradually rises to the upper layers of the atmosphere, where, under the influence of ultraviolet rays, it begins to slowly oxidize with molecular oxygen to form free NITROGEN and water: NH3 + O2 => N2 + H2O. Since nitrogen is a relatively heavy gas, it is retained gravitational field Earth. Finally, do not forget that under NORMAL conditions N2 is a very chemically inert substance; this factor also contributes to the accumulation of molecular nitrogen in the atmosphere of our planet.
Marat
Enlightened
(25806)
Re: "I still don't understand why there is so little nitrogen in the atmospheres of Mars and Venus."
Because there has never been biomass in such quantity as on Earth.
Re: "Probably you want to say that on other planets, nitrogen is mainly represented by ammonia."
I didn't say that 🙂
Re: "Ammonia is light and therefore leaks out of the atmosphere."
Does not leak, but reaches the zone of action of ultraviolet rays.
Re: "But the fact of the matter is that ammonia in the atmospheres of Mars and Venus is even less than helium (helium is a very light gas)"
I agree.
Re "Yes, and there is nothing to form ammonia from there, there is no life, there is no organic matter."
Right, I meant the same.

Answer from Yoergey Zaika[guru]
hello, no, but the giant planets, Jupiter and Saturn, is there no nitrogen there either? Paragraph... Nitrogen itself is chemically neutral and there is so much of it, other gases are more chemically aggressive and react with everything and everything, and that is in a bound state in the form of salts and minerals in rocks.

Answer from Kirill Nikitin[guru]
I'm not sure, but I think this is due to the increased nitrogen cycle under the action of living organisms (proteins)

Answer from Mikhail Levin[guru]
I'll try to think...
Nitrogen is a very common element, so there should be plenty of it everywhere.
The presence of gas in the atmosphere depends on the balance of arrival (from the bowels of the planet) and escape into outer space.
Nitrogen is lighter than CO2, so it leaves faster. Mars, most likely, simply cannot hold it (as the Earth cannot hold hydrogen or helium).
But with Venus - a big question. It has 4% nitrogen in the atmosphere, but the atmosphere itself is monstrous, it is not a fact that in absolute numbers it has less nitrogen than the Earth.
Another thing is that the Earth has very little carbon dioxide(although it stands out from the bowels). Here the matter is already in the presence of water and life that binds it.

Answer from ARTYOM.[master]
Atmospheric nitrogen fixation in nature occurs in two main directions - abiogenic and biogenic. The first route involves mainly the reactions of nitrogen with oxygen. Since nitrogen is chemically very inert, large amounts of energy (high temperatures) are required for oxidation. These conditions are achieved during lightning discharges, when the temperature reaches 25,000 °C or more. In this case, the formation of various nitrogen oxides occurs. There is also a possibility that abiotic fixation occurs as a result of photocatalytic reactions on the surfaces of semiconductors or broadband dielectrics (desert sand).
However, the main part of molecular nitrogen (about 1.4 108 t/year) is fixed biotically. For a long time it was believed that only a small number of microbial species (although widely distributed on the Earth’s surface) can bind molecular nitrogen: bacteria Azotobacter and Clostridium, nodule bacteria of legume plants Rhizobium, cyanobacteria Anabaena, Nostoc, etc. Now it is known that many other organisms in water and soil, for example, actinomycetes in tubers of alder and other trees (160 species in total). All of them convert molecular nitrogen into ammonium compounds (NH4+). This process requires a significant amount of energy (to fix 1 g of atmospheric nitrogen, bacteria in legume nodules spend about 167.5 kJ, that is, they oxidize about 10 g of glucose). Thus, the mutual benefit of the symbiosis of plants and nitrogen-fixing bacteria is visible - the former provide the latter with a “place to live” and supply the “fuel” obtained as a result of photosynthesis - glucose, the latter provide the nitrogen necessary for plants in the form they assimilate.
Nitrogen in the form of ammonia and ammonium compounds, obtained in the processes of biogenic nitrogen fixation, is rapidly oxidized to nitrates and nitrites (this process is called nitrification). The latter, not connected by plant tissues (and further along the food chain by herbivores and predators), do not remain in the soil for long. Most nitrates and nitrites are highly soluble, so they are washed off by water and eventually enter the world's oceans (this flow is estimated at 2.5-8 107 tons / year).
Nitrogen included in the tissues of plants and animals, after their death, undergoes ammonification (the decomposition of complex compounds containing nitrogen with the release of ammonia and ammonium ions) and denitrification, that is, the release of atomic nitrogen, as well as its oxides. These processes are entirely due to the activity of microorganisms in aerobic and anaerobic conditions.
In the absence of human activity, the processes of nitrogen fixation and nitrification are almost completely balanced by opposite reactions of denitrification. Part of the nitrogen enters the atmosphere from the mantle with volcanic eruptions, part is firmly fixed in soils and clay minerals, in addition, nitrogen is constantly leaking from the upper layers of the atmosphere into interplanetary space.

Nitrogen is a moderately active element that reacts poorly with natural inorganic compounds. Therefore, there is a high probability that a significant amount of this gas was contained in the primary atmosphere. In this case, a significant part of the nitrogen of the modern atmosphere is relic, preserved since the formation of the Earth about 4.6 billion years ago, although another part of it could be degassed from the mantle already at the geological stage of the development of our planet. It should be taken into account that with the appearance of life on Earth about 4.0-3.8 billion years ago, this gas was constantly bound in organic matter and buried in ocean sediments, and after the emergence of life on land (about 400 million years ago) - and in continental deposits. Therefore, the vital activity of organisms over a long period of development of terrestrial life could significantly reduce the partial pressure of nitrogen in the Earth's atmosphere, thereby changing the climate of the Earth. When calculating the effect of nitrogen absorption, it should be taken into account that organic nitrogen (Norg) of oceanic sediments, together with sediments, was constantly removed from the oceans through zones of oceanic crust crowding in the Archaean or through zones of plate underthrust in the Proterozoic and Phanerozoic. After that, it was partly included in the granite-metamorphic rocks of the continental crust or went into the mantle, but partly again degassed and again entered the atmosphere.

In addition to the biogenic process of atmospheric nitrogen fixation, apparently, there is a rather effective abiogenic mechanism of the same direction. So, according to the calculations of J. Jung and M. McElroy (Yung, McElroy, 1979), nitrogen fixation in soils can occur during thunderstorms due to the formation of nitric and nitrous acids during electrical discharges in moist air.

Estimating the amount of nitrogen removed from the atmosphere is difficult, but possible. The nitrogen content of sedimentary rocks is usually directly correlated with the concentration of organic carbon buried in them. Therefore, the amount of nitrogen buried in oceanic sediments can apparently be estimated from the data on the mass of organic carbon buried in them, Corg. To do this, you only need to determine the coefficient of proportionality between H org and C org. In bottom sediments of the open ocean, Corg: Norg: Porg is approximately equal to 106:20:0.91 (Lisitsyn and Vinogradov, 1982), but up to 80% of nitrogen quickly leaves organic matter, therefore, the ratio Corg:Norg in sediments can increase up to 1:0.04. According to G. Faure (1989), this ratio in sediments is approximately 1:0.05. Let us accept, according to the data of A. B. Ronov and A. A. Yaroshevsky (1978, 1993), that about (2.7-2.86) × 10 sediments of the continents - about (9.2-8.09) × 10 21 g C org. Following G. Fore, we took the values of the ratios Corg: Norg close to 20:1, then the content of Horg in the sediments of the ocean floor and shelves is approximately equal to 1.36 × 10 20 g, and in continental sediments - 5.0 × 10 20

As a first approximation, we will assume that the development of life in the ocean is limited by the content of dissolved phosphorus in ocean waters, and its concentration changed insignificantly over time (Schopf, 1982). It follows that ocean biomass has always remained approximately proportional to the mass of water in the ocean itself. The evolution of the mass of water in the World Ocean was considered in fig. 112, curve 2). Taking into account the assumption made about the proportionality of the biomass in the oceans to the mass of the oceanic waters themselves, we can approximately take into account the removal of Norg along with oceanic sediments through the zones of crowding and subduction lithospheric plates during geological development Earth. Appropriate calculations (Sorokhtin, Ushakov, 1998) showed that during the geological development of the Earth (i.e. over the past 3.8-4 billion years), due to the process under consideration, about 19.2 × 10 20 g of nitrogen was removed from the Earth's atmosphere. To this amount of nitrogen it is necessary to add another mass of Norg ≈ 5.0 × 10 20 g, conserved in the sediments of the continents and accumulated there over a period of about 400 million years. Thus, in total, during the life of the Earth, approximately 24.2 × 10 20 g of nitrogen was removed from its atmosphere, which is equivalent to a decrease in atmospheric pressure by 474 mbar (for comparison, the partial pressure of nitrogen in the modern atmosphere is 765 mbar).

Let's consider two extreme cases. Let us first assume that nitrogen degassing from the mantle did not occur at all, then it is possible to determine the initial effective pressure of the Earth's atmosphere in the catarchean (ie, in the interval of 4.6-4.0 billion years). It turns out to be approximately equal to 1.23 bar (1.21 atm).

In the second case, we will assume, as was done in (Sorokhtin and Ushakov, 1991), that almost all nitrogen in the atmosphere has been degassed from the mantle over the past 4 billion years. The process of nitrogen degassing from the mantle was calculated using expressions (29) and (30), taking into account that the atmosphere currently contains 3.87 × 10 21 g of nitrogen, its content in rocks and sediments reaches 3.42 × 10 20 g, and in the nitrogen mantle approximately 4.07 × 10 21 g (Sorokhtin, Ushakov, 1998). The nitrogen mobility index should not change with time and was approximately equal to χ(N 2) ≈ 0.934. After calculating the accumulation of nitrogen in the outer geospheres of the Earth, the obtained results were corrected for the absorption of this gas in organic matter and its burial in rocks and sediments. The remaining part characterized the evolution of the mass of nitrogen in the Earth's atmosphere under the condition of its complete degassing from the mantle.

For both options, the evolution curves of the partial pressure of nitrogen in the Earth's atmosphere were then calculated (Fig. 117, curves 1 and 3). The real picture of the change in this pressure would then have to correspond to some intermediate curve, the position of which can be determined only by using Additional information according to the climates of the Earth that existed in past geological epochs. Such a reference point, for example, can be information about the development of the most grandiose glaciation of the continents in the early Proterozoic, about 2.5-2.3 billion years ago. As shown in Chap. 8, the continental masses were then located in low latitudes (see Fig. 98), but at the same time they were high above the ocean level (with average heights of about 4-3 km). Therefore, the occurrence of such glaciation could occur only if the average temperature earth's surface at sea level then did not exceed +6 ... +7 ° С, i.e. was approximately 280 K.

Figure 117.
1 - according to the hypothesis of the primacy of the nitrogen atmosphere; 2 - accepted option; 3 - according to the hypothesis of degassing of the nitrogen atmosphere from the mantle.

Figure 98.
1, tillites and tilloids; 2, consolidated continental crust; arrows on the Canadian Shield show the revealed directions of glacial shading; in white - the area of glaciation. Av - Australia; SAM and UAm - Northern and South America; An - Antarctica; ZAF - West Africa; Af - Africa; Ev - Europe; Ying - India; K - Northern and Southern China; Sat - Siberia.

It will be shown below that in the early Proterozoic the atmosphere practically consisted only of nitrogen with a small addition of argon, while partial pressures oxygen and carbon dioxide did not exceed 10 -6 and 10 -2 atm, respectively, and the solar constant was S = 1.14 × 10 6 erg / cm 2 × s. Assuming T s ≈ 280 K ≈ 7 °C for that cold epoch, we found, according to the adiabatic theory of the greenhouse effect described below, that the pressure of the nitrogen atmosphere at that time was approximately equal to p N 2 = 1.09 atm, while according to the primacy hypothesis nitrogen atmosphere at that time should have been p N 2 ≈ 1.19 atm, and according to the hypothesis of nitrogen completely degassed from the mantle, p N 2 ≈ 0.99 atm. This shows that the nitrogen of the modern atmosphere is approximately 54% of relict gas and only 46% is degassed from the mantle, and the most probable regularity in the evolution of nitrogen pressure in the Earth's atmosphere is shown in Fig. 117, curve 2.

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The role of nitrogen in the Earth's atmosphere.

Nitrogen is the main element of the Earth's atmosphere. Its main role is to regulate the rate of oxidation by diluting oxygen. Thus, nitrogen affects the speed and intensity of biological processes.

There are two interconnected ways to extract nitrogen from the Earth's atmosphere:

1) inorganic,
2) biochemical.

Figure 1. Geochemical nitrogen cycle (V.A. Vronsky, G.V. Voitkevich)

Inorganic extraction of nitrogen from the Earth's atmosphere.

In the Earth's atmosphere under the action of electrical discharges (during a thunderstorm) or in the process of photo chemical reactions(solar radiation) nitrogen compounds are formed (N 2 O, N 2 O 5, NO 2, NH 3, etc.). These compounds, dissolving in rainwater, fall to the ground along with precipitation, falling into the soil and water of the oceans.

Biological nitrogen fixation

Biological binding of atmospheric nitrogen is carried out:

- in the soil - nodule bacteria in symbiosis with higher plants,
- in water - plankton microorganisms and algae.

The amount of biologically bound nitrogen is much greater than the inorganically fixed one.

How does nitrogen get back into the Earth's atmosphere?

The remains of living organisms decompose as a result of exposure to numerous microorganisms. In the process, nitrogen, which is part of the proteins of organisms, undergoes a series of transformations:

- in the process of protein decomposition, ammonia and its derivatives are formed, which then enter the air and into ocean water,
- further ammonia and other nitrogen-containing organic compounds under the influence of bacteria Nitrosomonas and nitrobacteria form various nitrogen oxides (N 2 O, NO, N 2 O 3 and N 2 O 5). This process is called nitrification,
— Nitric acid when interacting with metals, it gives salts. These salts are attacked by denitrifying bacteria,
- in the process denitrification elemental nitrogen is formed, which returns back to the atmosphere (an example is underground gas jets consisting of pure N 2).

Where is nitrogen found?

Nitrogen enters the Earth's atmosphere through volcanic eruptions in the form of ammonia. Getting into the upper atmosphere, ammonia (NH 3) is oxidized and releases nitrogen (N 2).

Nitrogen is also buried in sedimentary rocks and is found in large quantities in bituminous deposits. However, this nitrogen also enters the atmosphere during the regional metamorphism of these rocks.

Thus, the main form of nitrogen presence on the surface of our planet is molecular nitrogen (N 2) in the composition of the Earth's atmosphere.

This was the article Nitrogen in the composition of the Earth's atmosphere - the content in the atmosphere is 78%. ". Read further: « Oxygen in the composition of the Earth's atmosphere - the content in the atmosphere is 21%.«

Articles on the topic "Atmosphere of the Earth":

The impact of the Earth's atmosphere on the human body with increasing altitude.
Height and boundaries of the Earth's atmosphere.

The structure and composition of the Earth's atmosphere, it must be said, have not always been constants at any given time in the development of our planet. Today, the vertical structure of this element, which has a total "thickness" of 1.5-2.0 thousand km, is represented by several main layers, including:

Troposphere.
tropopause.
Stratosphere.
Stratopause.
mesosphere and mesopause.
Thermosphere.
exosphere.

Basic elements of the atmosphere

The troposphere is a layer in which strong vertical and horizontal movements are observed, it is here that the weather, precipitation phenomena, climatic conditions. It extends for 7-8 kilometers from the surface of the planet almost everywhere, with the exception of the polar regions (there - up to 15 km). In the troposphere, there is a gradual decrease in temperature, approximately 6.4 ° C with each kilometer of altitude. This figure may differ for different latitudes and seasons.

The composition of the Earth's atmosphere in this part is represented by the following elements and their percentages:

Nitrogen - about 78 percent;

Oxygen - almost 21 percent;

Argon - about one percent;

Carbon dioxide - less than 0.05%.

Single composition up to a height of 90 kilometers

In addition, dust, water droplets, water vapor, combustion products, ice crystals, sea salts, many aerosol particles, etc. can be found here. This composition of the Earth’s atmosphere is observed up to approximately ninety kilometers in height, so the air is approximately the same in chemical composition, not only in the troposphere, but also in the upper layers. But there the atmosphere is fundamentally different. physical properties. The layer that has a common chemical composition is called the homosphere.

What other elements are in the Earth's atmosphere? As a percentage (by volume, in dry air), gases such as krypton (about 1.14 x 10 -4), xenon (8.7 x 10 -7), hydrogen (5.0 x 10 -5), methane (about 1.7 x 10 - 4), nitrous oxide (5.0 x 10 -5), etc. In terms of mass percentage of the listed components, nitrous oxide and hydrogen are the most, followed by helium, krypton, etc.

Physical properties of different atmospheric layers

The physical properties of the troposphere are closely related to its attachment to the surface of the planet. Hence the reflected solar heat in the form of infrared rays is sent back up, including the processes of heat conduction and convection. That is why the temperature drops with distance from the earth's surface. Such a phenomenon is observed up to the height of the stratosphere (11-17 kilometers), then the temperature becomes practically unchanged up to the level of 34-35 km, and then there is again an increase in temperatures to heights of 50 kilometers (the upper boundary of the stratosphere). Between the stratosphere and the troposphere there is a thin intermediate layer of the tropopause (up to 1-2 km), where constant temperatures are observed above the equator - about minus 70 ° C and below. Above the poles, the tropopause "warms up" in summer to minus 45°C, in winter temperatures here fluctuate around -65°C.

The gas composition of the Earth's atmosphere includes important element like ozone. There is relatively little of it near the surface (ten to the minus sixth power of a percent), since the gas is formed under the influence of sunlight from atomic oxygen in the upper parts of the atmosphere. In particular, most of the ozone is at an altitude of about 25 km, and the entire "ozone screen" is located in areas from 7-8 km in the region of the poles, from 18 km at the equator and up to fifty kilometers in general above the surface of the planet.

Atmosphere protects from solar radiation

The composition of the air in the Earth's atmosphere plays a very important role in the preservation of life, since individual chemical elements and compositions successfully restrict access solar radiation to the earth's surface and the people, animals, and plants living on it. For example, water vapor molecules effectively absorb almost all ranges of infrared radiation, except for lengths in the range from 8 to 13 microns. Ozone, on the other hand, absorbs ultraviolet up to a wavelength of 3100 A. Without its thin layer (on average 3 mm if placed on the surface of the planet), only water at a depth of more than 10 meters and underground caves, where solar radiation does not reach, can be inhabited. .

Zero Celsius at stratopause

Between the next two levels of the atmosphere, the stratosphere and the mesosphere, there is a remarkable layer - the stratopause. It approximately corresponds to the height of ozone maxima and here a relatively comfortable temperature for humans is observed - about 0°C. Above the stratopause, in the mesosphere (begins somewhere at an altitude of 50 km and ends at an altitude of 80-90 km), there is again a drop in temperature with increasing distance from the Earth's surface (up to minus 70-80 ° C). In the mesosphere, meteors usually burn out completely.

In the thermosphere - plus 2000 K!

Chemical composition of the Earth's atmosphere in the thermosphere (begins after the mesopause from altitudes of about 85-90 to 800 km) determines the possibility of such a phenomenon as the gradual heating of layers of very rarefied "air" under the influence of solar radiation. In this part of the "air cover" of the planet, temperatures from 200 to 2000 K occur, which are obtained in connection with the ionization of oxygen (above 300 km is atomic oxygen), as well as the recombination of oxygen atoms into molecules, accompanied by the release of a large amount of heat. The thermosphere is where the auroras originate.

Above the thermosphere is the exosphere - the outer layer of the atmosphere, from which light and rapidly moving hydrogen atoms can escape into outer space. The chemical composition of the Earth's atmosphere here is represented more by individual oxygen atoms in the lower layers, helium atoms in the middle, and almost exclusively hydrogen atoms in the upper. High temperatures prevail here - about 3000 K and there is no atmospheric pressure.

How was the earth's atmosphere formed?

But, as mentioned above, the planet did not always have such a composition of the atmosphere. In total, there are three concepts of the origin of this element. The first hypothesis assumes that the atmosphere was taken in the process of accretion from a protoplanetary cloud. However, today this theory is subject to significant criticism, since such a primary atmosphere must have been destroyed by the solar "wind" from a star in our planetary system. In addition, it is assumed that volatile elements could not stay in the planet formation zone according to the type terrestrial group due to too high temperatures.

The composition of the Earth's primary atmosphere, as suggested by the second hypothesis, could be formed due to the active bombardment of the surface by asteroids and comets that arrived from the vicinity of the solar system on early stages development. It is quite difficult to confirm or refute this concept.

Experiment at IDG RAS

The most plausible is the third hypothesis, which believes that the atmosphere appeared as a result of the release of gases from the mantle. earth's crust approximately 4 billion years ago. This concept was tested at the Institute of Geology and Geochemistry of the Russian Academy of Sciences in the course of an experiment called "Tsarev 2", when a sample of a meteoric substance was heated in a vacuum. Then, the release of such gases as H 2, CH 4, CO, H 2 O, N 2, etc. was recorded. Therefore, scientists rightly assumed that the chemical composition of the Earth's primary atmosphere included water and carbon dioxide, hydrogen fluoride vapor (HF), carbon monoxide(CO), hydrogen sulfide (H 2 S), nitrogen compounds, hydrogen, methane (CH 4), ammonia vapor (NH 3), argon, etc. Water vapor from the primary atmosphere participated in the formation of the hydrosphere, carbon dioxide was to a greater extent in bound state in organic matter and rocks, nitrogen passed into the composition of modern air, and again into sedimentary rocks and organic matter.

The composition of the Earth's primary atmosphere would not allow modern people be in it without breathing apparatus, since there was no oxygen in the required quantities then. This element appeared in significant amounts one and a half billion years ago, as is believed, in connection with the development of the process of photosynthesis in blue-green and other algae, which are the oldest inhabitants of our planet.

Oxygen minimum

The fact that the composition of the Earth's atmosphere was initially almost anoxic is indicated by the fact that easily oxidized, but not oxidized graphite (carbon) is found in the most ancient (Katarchean) rocks. Subsequently, the so-called banded iron ores appeared, which included interlayers of enriched iron oxides, which means the appearance on the planet of a powerful source of oxygen in molecular form. But these elements came across only periodically (perhaps the same algae or other oxygen producers appeared as small islands in an anoxic desert), while the rest of the world was anaerobic. The latter is supported by the fact that easily oxidizable pyrite was found in the form of pebbles processed by the flow without traces of chemical reactions. Since flowing waters cannot be poorly aerated, the view has evolved that the pre-Cambrian atmosphere contained less than one percent oxygen of today's composition.

Revolutionary change in air composition

Approximately in the middle of the Proterozoic (1.8 billion years ago), the “oxygen revolution” took place, when the world switched to aerobic respiration, during which 38 can be obtained from one nutrient molecule (glucose), and not two (as with anaerobic respiration) units of energy. The composition of the Earth's atmosphere, in terms of oxygen, began to exceed one percent of the modern one, began to appear ozone layer protecting organisms from radiation. It was from her that “hidden” under thick shells, for example, such ancient animals as trilobites. From then until our time, the content of the main "respiratory" element has gradually and slowly increased, providing a variety of development of life forms on the planet.

Atmosphere(from the Greek atmos - steam and spharia - ball) - the air shell of the Earth, rotating with it. The development of the atmosphere was closely connected with the geological and geochemical processes taking place on our planet, as well as with the activities of living organisms.

The lower boundary of the atmosphere coincides with the surface of the Earth, since air penetrates into the smallest pores in the soil and is dissolved even in water.

The upper limit at an altitude of 2000-3000 km gradually passes into outer space.

Oxygen-rich atmosphere makes life possible on Earth. Atmospheric oxygen is used in the process of breathing by humans, animals, and plants.

If there were no atmosphere, the Earth would be as quiet as the moon. After all, sound is the vibration of air particles. The blue color of the sky is explained by the fact that the sun's rays, passing through the atmosphere, as if through a lens, are decomposed into their component colors. In this case, the rays of blue and blue colors are scattered most of all.

The atmosphere retains most of the ultraviolet radiation from the Sun, which has a detrimental effect on living organisms. It also keeps heat at the surface of the Earth, preventing our planet from cooling.

The structure of the atmosphere

Several layers can be distinguished in the atmosphere, differing in density and density (Fig. 1).

Troposphere

Troposphere- the lowest layer of the atmosphere, whose thickness above the poles is 8-10 km, in temperate latitudes - 10-12 km, and above the equator - 16-18 km.

Rice. 1. The structure of the Earth's atmosphere

The air in the troposphere is heated from the earth's surface, i.e. from land and water. Therefore, the air temperature in this layer decreases with height by an average of 0.6 °C for every 100 m. At the upper boundary of the troposphere, it reaches -55 °C. At the same time, in the region of the equator at the upper boundary of the troposphere, the air temperature is -70 ° C, and in the region North Pole-65 °С.

About 80% of the mass of the atmosphere is concentrated in the troposphere, almost all water vapor is located, thunderstorms, storms, clouds and precipitation occur, and vertical (convection) and horizontal (wind) air movement occurs.

We can say that the weather is mainly formed in the troposphere.

Stratosphere

Stratosphere- the layer of the atmosphere located above the troposphere at an altitude of 8 to 50 km. The color of the sky in this layer appears purple, which is explained by the rarefaction of the air, due to which the sun's rays almost do not scatter.

The stratosphere contains 20% of the mass of the atmosphere. The air in this layer is rarefied, there is practically no water vapor, and therefore clouds and precipitation are almost not formed. However, stable air currents are observed in the stratosphere, the speed of which reaches 300 km / h.

This layer is concentrated ozone(ozone screen, ozonosphere), a layer that absorbs ultraviolet rays, preventing them from passing to the Earth and thereby protecting living organisms on our planet. Due to ozone, the air temperature at the upper boundary of the stratosphere is in the range from -50 to 4-55 °C.

Between the mesosphere and the stratosphere there is a transitional zone - the stratopause.

Mesosphere

Mesosphere- a layer of the atmosphere located at an altitude of 50-80 km. The air density here is 200 times less than at the surface of the Earth. The color of the sky in the mesosphere appears black, stars are visible during the day. The air temperature drops to -75 (-90)°C.

At an altitude of 80 km begins thermosphere. The air temperature in this layer rises sharply to a height of 250 m, and then becomes constant: at a height of 150 km it reaches 220-240 °C; at an altitude of 500-600 km it exceeds 1500 °C.

In the mesosphere and thermosphere, under the action of cosmic rays, gas molecules break up into charged (ionized) particles of atoms, so this part of the atmosphere is called ionosphere- a layer of very rarefied air, located at an altitude of 50 to 1000 km, consisting mainly of ionized oxygen atoms, nitric oxide molecules and free electrons. This layer is characterized by high electrification, and long and medium radio waves are reflected from it, as from a mirror.

In the ionosphere, auroras arise - the glow of rarefied gases under the influence of electrically charged particles flying from the Sun - and sharp fluctuations in the magnetic field are observed.

Exosphere

Exosphere- the outer layer of the atmosphere, located above 1000 km. This layer is also called the scattering sphere, since gas particles move here at high speed and can be scattered into outer space.

Composition of the atmosphere

The atmosphere is a mixture of gases consisting of nitrogen (78.08%), oxygen (20.95%), carbon dioxide (0.03%), argon (0.93%), a small amount of helium, neon, xenon, krypton (0.01%), ozone and other gases, but their content is negligible (Table 1). Modern composition The air of the Earth was established more than a hundred million years ago, but the sharply increased human production activity nevertheless led to its change. Currently, there is an increase in the content of CO 2 by about 10-12%.

The gases that make up the atmosphere perform various functional roles. However, the main significance of these gases is determined primarily by the fact that they very strongly absorb radiant energy and thus have a significant effect on the temperature regime of the Earth's surface and atmosphere.

Table 1. Chemical composition of dry atmospheric air near the earth's surface

	Volume concentration. %	Molecular weight, units

Oxygen

Carbon dioxide





Nitrous oxide
	0 to 0.00001
Sulfur dioxide	from 0 to 0.000007 in summer; 0 to 0.000002 in winter
	From 0 to 0.000002	46,0055/17,03061
Azog dioxide

Carbon monoxide

Nitrogen, the most common gas in the atmosphere, chemically little active.

Oxygen, unlike nitrogen, is a chemically very active element. The specific function of oxygen is the oxidation of organic matter of heterotrophic organisms, rocks, and incompletely oxidized gases emitted into the atmosphere by volcanoes. Without oxygen, there would be no decomposition of dead organic matter.

The role of carbon dioxide in the atmosphere is exceptionally great. It enters the atmosphere as a result of the processes of combustion, respiration of living organisms, decay and is, first of all, the main building material for the creation of organic matter during photosynthesis. In addition, the property of carbon dioxide to transmit short-wave solar radiation and absorb part of thermal long-wave radiation is of great importance, which will create the so-called greenhouse effect, which will be discussed below.

The influence on atmospheric processes, especially on the thermal regime of the stratosphere, is also exerted by ozone. This gas serves as a natural absorber of solar ultraviolet radiation, and the absorption of solar radiation leads to air heating. The average monthly values of the total ozone content in the atmosphere vary depending on the latitude of the area and the season within 0.23-0.52 cm (this is the thickness of the ozone layer at ground pressure and temperature). There is an increase in the ozone content from the equator to the poles and an annual variation with a minimum in autumn and a maximum in spring.

A characteristic property of the atmosphere can be called the fact that the content of the main gases (nitrogen, oxygen, argon) changes slightly with height: at an altitude of 65 km in the atmosphere, the content of nitrogen is 86%, oxygen - 19, argon - 0.91, at an altitude of 95 km - nitrogen 77, oxygen - 21.3, argon - 0.82%. The constancy of the composition of atmospheric air vertically and horizontally is maintained by its mixing.

In addition to gases, air contains water vapor and solid particles. The latter can have both natural and artificial (anthropogenic) origin. These are flower pollen, tiny salt crystals, road dust, aerosol impurities. When the sun's rays penetrate the window, they can be seen with the naked eye.

There are especially many particulate matter in the air of cities and large industrial centers, where emissions of harmful gases and their impurities formed during fuel combustion are added to aerosols.

The concentration of aerosols in the atmosphere determines the transparency of the air, which affects the solar radiation reaching the Earth's surface. The largest aerosols are condensation nuclei (from lat. condensatio- compaction, thickening) - contribute to the transformation of water vapor into water droplets.

The value of water vapor is determined primarily by the fact that it delays the long-wave thermal radiation of the earth's surface; represents the main link of large and small moisture cycles; raises the temperature of the air when the water beds condense.

The amount of water vapor in the atmosphere varies over time and space. Thus, the concentration of water vapor near the earth's surface ranges from 3% in the tropics to 2-10 (15)% in Antarctica.

The average content of water vapor in the vertical column of the atmosphere in temperate latitudes is about 1.6-1.7 cm (the layer of condensed water vapor will have such a thickness). Information about water vapor in different layers of the atmosphere is contradictory. It was assumed, for example, that in the altitude range from 20 to 30 km, the specific humidity strongly increases with height. However, subsequent measurements indicate a greater dryness of the stratosphere. Apparently, the specific humidity in the stratosphere depends little on height and amounts to 2–4 mg/kg.

The variability of water vapor content in the troposphere is determined by the interaction of evaporation, condensation, and horizontal transport. As a result of the condensation of water vapor, clouds form and precipitation occurs in the form of rain, hail and snow.

The processes of phase transitions of water proceed mainly in the troposphere, which is why clouds in the stratosphere (at altitudes of 20-30 km) and mesosphere (near the mesopause), called mother-of-pearl and silver, are observed relatively rarely, while tropospheric clouds often cover about 50% of the entire earth surfaces.

The amount of water vapor that can be contained in the air depends on the temperature of the air.

1 m 3 of air at a temperature of -20 ° C can contain no more than 1 g of water; at 0 °C - no more than 5 g; at +10 °С - no more than 9 g; at +30 °С - no more than 30 g of water.

Conclusion: The higher the air temperature, the more water vapor it can contain.

Air can be rich and not saturated steam. So, if at a temperature of +30 ° C 1 m 3 of air contains 15 g of water vapor, the air is not saturated with water vapor; if 30 g - saturated.

Absolute humidity- this is the amount of water vapor contained in 1 m 3 of air. It is expressed in grams. For example, if they say "absolute humidity is 15", then this means that 1 mL contains 15 g of water vapor.

Relative humidity- this is the ratio (in percent) of the actual content of water vapor in 1 m 3 of air to the amount of water vapor that can be contained in 1 m L at a given temperature. For example, if a weather report is broadcast over the radio that the relative humidity is 70%, this means that the air contains 70% of the water vapor that it can hold at a given temperature.

The greater the relative humidity of the air, t. the closer the air is to saturation, the more likely it is to fall.

Always high (up to 90%) relative humidity is observed in the equatorial zone, since there is a high air temperature throughout the year and there is a large evaporation from the surface of the oceans. The same high relative humidity is in the polar regions, but only because at low temperatures even a small amount of water vapor makes the air saturated or close to saturation. In temperate latitudes, relative humidity varies seasonally - it is higher in winter and lower in summer.

The relative humidity of the air is especially low in deserts: 1 m 1 of air there contains two to three times less than the amount of water vapor possible at a given temperature.

To measure relative humidity, a hygrometer is used (from the Greek hygros - wet and metreco - I measure).

When cooled, saturated air cannot retain the same amount of water vapor in itself, it thickens (condenses), turning into droplets of fog. Fog can be observed in the summer on a clear cool night.

Clouds- this is the same fog, only it is formed not at the earth's surface, but at a certain height. As the air rises, it cools and the water vapor in it condenses. The resulting tiny droplets of water make up the clouds.

involved in the formation of clouds particulate matter suspended in the troposphere.

Clouds may have different shape, which depends on the conditions of their formation (Table 14).

The lowest and heaviest clouds are stratus. They are located at an altitude of 2 km from the earth's surface. At an altitude of 2 to 8 km, more picturesque cumulus clouds can be observed. The highest and lightest are cirrus clouds. They are located at an altitude of 8 to 18 km above the earth's surface.

families	Kinds of clouds	Appearance
A. Upper clouds - above 6 km	I. Pinnate	Threadlike, fibrous, white
	II. cirrocumulus	Layers and ridges of small flakes and curls, white
	III. Cirrostratus	Transparent whitish veil
B. Clouds of the middle layer - above 2 km	IV. Altocumulus	Layers and ridges of white and gray
B. Clouds of the middle layer - above 2 km	V. Altostratus	Smooth veil of milky gray color
B. Lower clouds - up to 2 km	VI. Nimbostratus	Solid shapeless gray layer
	VII. Stratocumulus	Opaque layers and ridges of gray
	VIII. layered	Illuminated gray veil
D. Clouds of vertical development - from the lower to the upper tier	IX. Cumulus	Clubs and domes bright white, with torn edges in the wind
	X. Cumulonimbus	Powerful cumulus-shaped masses of dark lead color

Atmospheric protection

The main source are industrial enterprises and cars. In large cities, the problem of gas contamination of the main transport routes is very acute. That is why in many major cities around the world, including in our country, introduced environmental control of the toxicity of car exhaust gases. According to experts, smoke and dust in the air can halve the flow of solar energy to the earth's surface, which will lead to a change in natural conditions.