The Earth's atmosphere is heterogeneous: different air densities and pressures are observed at different heights, temperature and gas composition change. Based on the behavior of the ambient temperature (i.e., the temperature rises with height or decreases), the following layers are distinguished in it: troposphere, stratosphere, mesosphere, thermosphere and exosphere. The boundaries between the layers are called pauses: there are 4 of them, because. the upper boundary of the exosphere is very blurred and often refers to the near space. The general structure of the atmosphere can be found in the attached diagram.
Fig.1 The structure of the Earth's atmosphere. Credit: website
The lowest atmospheric layer is the troposphere, the upper boundary of which, called the tropopause, varies depending on the geographical latitude and ranges from 8 km. in polar up to 20 km. in tropical latitudes. In middle or temperate latitudes, its upper limit lies at altitudes of 10-12 km. During the year, the upper limit of the troposphere experiences fluctuations depending on the influx of solar radiation. So, as a result of sounding at the South Pole of the Earth by the US meteorological service, it was revealed that from March to August or September there is a steady cooling of the troposphere, as a result of which, for a short period in August or September, its border rises to 11.5 km. Then, between September and December, it drops rapidly and reaches its lowest position - 7.5 km, after which its height remains practically unchanged until March. Those. The troposphere is at its thickest in summer and at its thinnest in winter.
It should be noted that in addition to seasonal variations, there are also daily fluctuations in the height of the tropopause. Also, its position is influenced by cyclones and anticyclones: in the first, it descends, because. the pressure in them is lower than in the surrounding air, and secondly, it rises accordingly.
The troposphere contains up to 90% of the total mass earth air and 9/10 of all water vapor. Turbulence is highly developed here, especially in the near-surface and highest layers, clouds of all tiers develop, cyclones and anticyclones form. And due to the accumulation of greenhouse gases (carbon dioxide, methane, water vapor) of the sun's rays reflected from the Earth's surface, the greenhouse effect develops.
The greenhouse effect is associated with a decrease in air temperature in the troposphere with height (because the heated Earth gives off more heat to the surface layers). The average vertical gradient is 0.65°/100 m (i.e. the air temperature drops by 0.65° C for every 100 meters you rise). So if at the surface of the Earth near the equator mean annual temperature air is + 26 ° then at the upper limit -70 °. The temperature in the tropopause region north pole during the year it changes from -45° in summer to -65° in winter.
As the altitude increases, the air pressure also decreases, amounting to only 12-20% of the near-surface level near the upper troposphere.
On the border of the troposphere and the overlying layer of the stratosphere lies the tropopause layer, 1-2 km thick. The air layer in which the vertical gradient decreases to 0.2°/100 m versus 0.65°/100 m in the underlying regions of the troposphere is usually taken as the lower boundaries of the tropopause.
Within the tropopause, air flows of a strictly defined direction are observed, called high-altitude jet streams or "jet streams", formed under the influence of the Earth's rotation around its axis and heating of the atmosphere with the participation of solar radiation. Currents are observed at the boundaries of zones with significant temperature differences. There are several centers of localization of these currents, for example, arctic, subtropical, subpolar and others. Knowing the localization of jet streams is very important for meteorology and aviation: the first uses streams for more accurate weather forecasting, the second for building aircraft flight routes, because At the flow boundaries there are strong turbulent vortices, similar to small whirlpools, called "clear sky turbulence" due to the absence of clouds at these altitudes.
Under the influence of high-altitude jet currents, ruptures often form in the tropopause, and at times it disappears altogether, though then it forms again. This is especially often observed in subtropical latitudes over which a powerful subtropical high-altitude current dominates. In addition, the difference between the layers of the tropopause in terms of ambient temperature leads to the formation of breaks. For example, a wide gap exists between the warm and low polar tropopause and the high and cold tropopause of tropical latitudes. V Lately the tropopause layer of temperate latitudes is also distinguished, which has breaks with the previous two layers: polar and tropical.
The second layer of the earth's atmosphere is the stratosphere. The stratosphere can be conditionally divided into 2 regions. The first of them, lying up to heights of 25 km, is characterized by almost constant temperatures, which are equal to the temperatures of the upper layers of the troposphere over a specific area. The second region, or inversion region, is characterized by an increase in air temperature to altitudes of about 40 km. This is due to the absorption of solar ultraviolet radiation by oxygen and ozone. In the upper part of the stratosphere, due to this heating, the temperature is often positive or even comparable to the surface air temperature.
Above the inversion region is a layer of constant temperatures, which is called the stratopause and is the boundary between the stratosphere and the mesosphere. Its thickness reaches 15 km.
Unlike the troposphere, turbulent disturbances are rare in the stratosphere, but strong horizontal winds or jet streams blowing in narrow zones along the borders of temperate latitudes facing the poles are noted. The position of these zones is not constant: they can shift, expand, or even disappear altogether. Often, jet streams penetrate into the upper layers of the troposphere, or vice versa, air masses from the troposphere penetrate into the lower layers of the stratosphere. Such mixing of air masses in areas of atmospheric fronts is especially characteristic.
Little in the stratosphere and water vapor. The air here is very dry, and therefore there are few clouds. Only at altitudes of 20-25 km, being in high latitudes, one can notice very thin mother-of-pearl clouds, consisting of supercooled water droplets. During the day, these clouds are not visible, but with the onset of darkness, they seem to glow due to their illumination by the Sun that has already set below the horizon.
At the same heights (20-25 km.) in the lower stratosphere there is the so-called ozone layer - the area with the highest ozone content, which is formed under the influence of ultraviolet solar radiation (you can learn more about this process on the page). The ozone layer or ozonosphere is essential to sustain life for all organisms living on land by absorbing deadly ultraviolet rays up to 290 nm. It is for this reason that living organisms do not live above the ozone layer, it is the upper limit of the spread of life on Earth.
Under the influence of ozone, magnetic fields also change, atoms break up molecules, ionization occurs, new formation of gases and other chemical compounds.
The layer of the atmosphere above the stratosphere is called the mesosphere. It is characterized by a decrease in air temperature with height with an average vertical gradient of 0.25-0.3°/100 m, which leads to strong turbulence. At the upper boundaries of the mesosphere in the area called the mesopause, temperatures up to -138 ° C were noted, which is the absolute minimum for the entire atmosphere of the Earth as a whole.
Here, within the mesopause, the lower boundary of the region of active absorption of X-ray and short-wavelength ultraviolet radiation of the Sun passes. This energy process is called radiant heat transfer. As a result, the gas is heated and ionized, which causes the glow of the atmosphere.
At altitudes of 75-90 km near the upper boundaries of the mesosphere, special clouds were noted, occupying vast areas in the polar regions of the planet. These clouds are called silver because of their glow at dusk, which is due to the reflection of sunlight from the ice crystals of which these clouds are composed.
Air pressure within the mesopause is 200 times less than at the earth's surface. This suggests that almost all the air in the atmosphere is concentrated in its 3 lower layers: the troposphere, stratosphere and mesosphere. The overlying layers of the thermosphere and exosphere account for only 0.05% of the mass of the entire atmosphere.
The thermosphere lies at altitudes from 90 to 800 km above the Earth's surface.
The thermosphere is characterized by a continuous increase in air temperature up to altitudes of 200-300 km, where it can reach 2500°C. The increase in temperature occurs due to the absorption by gas molecules of the X-ray and short-wave part of the ultraviolet radiation of the Sun. Above 300 km above sea level, the temperature rise stops.
At the same time as the temperature rises, the pressure decreases, and, consequently, the density of the surrounding air. So if at the lower boundaries of the thermosphere the density is 1.8 × 10 -8 g / cm 3, then at the upper it is already 1.8 × 10 -15 g / cm 3, which approximately corresponds to 10 million - 1 billion particles in 1 cm 3 .
All characteristics of the thermosphere, such as the composition of air, its temperature, density, are subject to strong fluctuations: depending on the geographical location, season of the year and time of day. Even the location of the upper boundary of the thermosphere is changing.
The uppermost layer of the atmosphere is called the exosphere or scattering layer. Its lower limit is constantly changing within very wide limits; the height of 690-800 km was taken as the average value. It is set where the probability of intermolecular or interatomic collisions can be neglected, i.e. the average distance that a randomly moving molecule will cover before colliding with another similar molecule (the so-called free path) will be so large that, in fact, the molecules will not collide with a probability close to zero. The layer where the described phenomenon takes place is called the thermopause.
The upper boundary of the exosphere lies at altitudes of 2-3 thousand km. It is strongly blurred and gradually passes into the near space vacuum. Sometimes, for this reason, the exosphere is considered a part of outer space, and its upper boundary is taken to be a height of 190 thousand km, at which the effect of solar radiation pressure on the speed of hydrogen atoms exceeds the gravitational attraction of the Earth. This is the so-called. the earth's corona, which is made up of hydrogen atoms. The density of the earth's corona is very low: only 1000 particles per cubic centimeter, but even this number is more than 10 times higher than the concentration of particles in interplanetary space.
Due to the extremely rarefied air of the exosphere, particles move around the Earth in elliptical orbits without colliding with each other. Some of them, moving along open or hyperbolic trajectories with cosmic velocities (hydrogen and helium atoms), leave the atmosphere and go into outer space, which is why the exosphere is called the scattering sphere.
The composition of the earth. Air
Air is a mechanical mixture of various gases that make up the Earth's atmosphere. Air is essential for breathing living organisms finds wide application in industry.
The fact that air is a mixture, and not a homogeneous substance, was proved during the experiments of the Scottish scientist Joseph Black. During one of them, the scientist discovered that when white magnesia (magnesium carbonate) is heated, “bound air”, that is, carbon dioxide, is released, and burnt magnesia (magnesium oxide) is formed. In contrast, when limestone is fired, “bound air” is removed. Based on these experiments, the scientist concluded that the difference between carbonic and caustic alkalis is that the former includes carbon dioxide, which is one of the constituent parts air. Today we know that in addition to carbon dioxide, the composition of the earth's air includes:
The ratio of gases in the earth's atmosphere indicated in the table is typical for its lower layers, up to a height of 120 km. In these areas lies a well-mixed, homogeneous region, called the homosphere. Above the homosphere lies the heterosphere, which is characterized by the decomposition of gas molecules into atoms and ions. The regions are separated from each other by a turbopause.
The chemical reaction in which, under the influence of solar and cosmic radiation, molecules decompose into atoms, is called photodissociation. During the decay of molecular oxygen, atomic oxygen is formed, which is the main gas of the atmosphere at altitudes above 200 km. At altitudes above 1200 km, hydrogen and helium, which are the lightest of the gases, begin to predominate.
Since the bulk of the air is concentrated in the 3 lower atmospheric layers, changes in the air composition at altitudes above 100 km do not have a noticeable effect on the overall composition of the atmosphere.
Nitrogen is the most common gas, accounting for more than three-quarters of the earth's air volume. Modern nitrogen was formed by the oxidation of the early ammonia-hydrogen atmosphere with molecular oxygen, which is formed during photosynthesis. Currently, a small amount of nitrogen enters the atmosphere as a result of denitrification - the process of reduction of nitrates to nitrites, followed by the formation of gaseous oxides and molecular nitrogen, which is produced by anaerobic prokaryotes. Some nitrogen enters the atmosphere during volcanic eruptions.
In the upper atmosphere, when exposed to electrical discharges with the participation of ozone, molecular nitrogen is oxidized to nitrogen monoxide:
N 2 + O 2 → 2NO
Under normal conditions, the monoxide immediately reacts with oxygen to form nitrous oxide:
2NO + O 2 → 2N 2 O
Nitrogen is the most important chemical element in the earth's atmosphere. Nitrogen is part of proteins, provides mineral nutrition to plants. It determines the rate of biochemical reactions, plays the role of an oxygen diluent.
Oxygen is the second most abundant gas in the Earth's atmosphere. The formation of this gas is associated with the photosynthetic activity of plants and bacteria. And the more diverse and numerous photosynthetic organisms became, the more significant the process of oxygen content in the atmosphere became. A small amount of heavy oxygen is released during degassing of the mantle.
In the upper layers of the troposphere and stratosphere, under the influence of ultraviolet solar radiation (we denote it as hν), ozone is formed:
O 2 + hν → 2O
As a result of the action of the same ultraviolet radiation, ozone decays:
O 3 + hν → O 2 + O
O 3 + O → 2O 2
As a result of the first reaction, atomic oxygen is formed, as a result of the second - molecular oxygen. All 4 reactions are called the Chapman mechanism, after the British scientist Sidney Chapman who discovered them in 1930.
Oxygen is used for the respiration of living organisms. With its help, the processes of oxidation and combustion occur.
Ozone serves to protect living organisms from ultraviolet radiation, which causes irreversible mutations. The highest concentration of ozone is observed in the lower stratosphere within the so-called. ozone layer or ozone screen lying at altitudes of 22-25 km. The ozone content is small: at normal pressure, all the ozone of the earth's atmosphere would occupy a layer only 2.91 mm thick.
The formation of the third most common gas in the atmosphere, argon, as well as neon, helium, krypton and xenon, is associated with volcanic eruptions and the decay of radioactive elements.
In particular, helium is a product of the radioactive decay of uranium, thorium and radium: 238 U → 234 Th + α, 230 Th → 226 Ra + 4 He, 226 Ra → 222 Rn + α (in these reactions, the α-particle is a helium nucleus, which in in the process of energy loss captures electrons and becomes 4 He).
Argon is formed during the decay of the radioactive isotope of potassium: 40 K → 40 Ar + γ.
Neon escapes from igneous rocks.
Krypton is formed as the end product of the decay of uranium (235 U and 238 U) and thorium Th.
The bulk of atmospheric krypton was formed in the early stages of the Earth's evolution as a result of the decay of transuranium elements with a phenomenally short half-life or came from space, the content of krypton in which is ten million times higher than on Earth.
Xenon is the result of the fission of uranium, but most of this gas is left over from the early stages of the Earth's formation, from the primary atmosphere.
Carbon dioxide enters the atmosphere as a result of volcanic eruptions and in the process of decomposition of organic matter. Its content in the atmosphere of the middle latitudes of the Earth varies greatly depending on the seasons of the year: in winter, the amount of CO 2 increases, and in summer it decreases. This fluctuation is connected with the activity of plants that use carbon dioxide in the process of photosynthesis.
Hydrogen is formed as a result of the decomposition of water by solar radiation. But, being the lightest of the gases that make up the atmosphere, it constantly escapes into outer space, and therefore its content in the atmosphere is very small.
Water vapor is the result of the evaporation of water from the surface of lakes, rivers, seas and land.
The concentration of the main gases in the lower layers of the atmosphere, with the exception of water vapor and carbon dioxide, is constant. In small quantities, the atmosphere contains sulfur oxide SO 2, ammonia NH 3, carbon monoxide CO, ozone O 3, hydrogen chloride HCl, hydrogen fluoride HF, nitrogen monoxide NO, hydrocarbons, mercury vapor Hg, iodine I 2 and many others. In the lower atmospheric layer of the troposphere, there is constantly a large amount of suspended solid and liquid particles.
Sources of particulate matter in the Earth's atmosphere are volcanic eruptions, plant pollen, microorganisms, and, more recently, human activities such as the burning of fossil fuels in manufacturing processes. The smallest particles of dust, which are the nuclei of condensation, are the causes of the formation of fogs and clouds. Without solid particles constantly present in the atmosphere, precipitation would not fall on the Earth.
At sea level 1013.25 hPa (about 760 mmHg). The average global air temperature at the Earth's surface is 15°C, while the temperature varies from about 57°C in subtropical deserts to -89°C in Antarctica. Air density and pressure decrease with height according to a law close to exponential.
The structure of the atmosphere. Vertically, the atmosphere has a layered structure, determined mainly by the features of the vertical temperature distribution (figure), which depends on the geographical location, season, time of day, and so on. The lower layer of the atmosphere - the troposphere - is characterized by a drop in temperature with height (by about 6 ° C per 1 km), its height is from 8-10 km in polar latitudes to 16-18 km in the tropics. Due to the rapid decrease in air density with height, about 80% of the total mass of the atmosphere is in the troposphere. Above the troposphere is the stratosphere - a layer that is characterized in general by an increase in temperature with height. The transition layer between the troposphere and stratosphere is called the tropopause. In the lower stratosphere, up to a level of about 20 km, the temperature changes little with height (the so-called isothermal region) and often even slightly decreases. Higher, the temperature rises due to the absorption of solar UV radiation by ozone, slowly at first, and faster from a level of 34-36 km. The upper boundary of the stratosphere - the stratopause - is located at an altitude of 50-55 km, corresponding to the maximum temperature (260-270 K). The layer of the atmosphere, located at an altitude of 55-85 km, where the temperature drops again with height, is called the mesosphere, at its upper boundary - the mesopause - the temperature reaches 150-160 K in summer, and 200-230 K in winter. The thermosphere begins above the mesopause - a layer, characterized by a rapid increase in temperature, reaching values of 800-1200 K at an altitude of 250 km. The corpuscular and X-ray radiation of the Sun is absorbed in the thermosphere, meteors are slowed down and burned out, so it performs the function of the Earth's protective layer. Even higher is the exosphere, from where atmospheric gases are dissipated into world space due to dissipation and where a gradual transition from the atmosphere to interplanetary space takes place.
Composition of the atmosphere. Up to a height of about 100 km, the atmosphere is practically homogeneous in chemical composition and the average molecular weight of air (about 29) is constant in it. Near the Earth's surface, the atmosphere consists of nitrogen (about 78.1% by volume) and oxygen (about 20.9%), and also contains small amounts of argon, carbon dioxide (carbon dioxide), neon, and other constant and variable components (see Air ).
In addition, the atmosphere contains small amounts of ozone, nitrogen oxides, ammonia, radon, etc. The relative content of the main components of the air is constant over time and uniform in different geographical areas. The content of water vapor and ozone is variable in space and time; despite the low content, their role in atmospheric processes is very significant.
Above 100-110 km, the dissociation of oxygen, carbon dioxide and water vapor molecules occurs, so the molecular weight of air decreases. At an altitude of about 1000 km, light gases - helium and hydrogen - begin to predominate, and even higher, the Earth's atmosphere gradually turns into interplanetary gas.
The most important variable component of the atmosphere is water vapor, which enters the atmosphere through evaporation from the surface of water and moist soil, as well as through transpiration by plants. The relative content of water vapor varies near the earth's surface from 2.6% in the tropics to 0.2% in the polar latitudes. With height, it quickly falls, decreasing by half already at a height of 1.5-2 km. The vertical column of the atmosphere at temperate latitudes contains about 1.7 cm of the “precipitated water layer”. When water vapor condenses, clouds form, from which atmospheric precipitation falls in the form of rain, hail, and snow.
An important component of atmospheric air is ozone, 90% concentrated in the stratosphere (between 10 and 50 km), about 10% of it is in the troposphere. Ozone provides absorption of hard UV radiation (with a wavelength of less than 290 nm), and this is its protective role for the biosphere. The values of the total ozone content vary depending on the latitude and season, ranging from 0.22 to 0.45 cm (the thickness of the ozone layer at a pressure of p= 1 atm and a temperature of T = 0°C). V ozone holes observed in Antarctica in the spring since the early 1980s, the ozone content can drop to 0.07 cm. latitudes. An essential variable component of the atmosphere is carbon dioxide, the content of which in the atmosphere has increased by 35% over the past 200 years, which is mainly explained by the anthropogenic factor. Its latitudinal and seasonal variability is observed, associated with plant photosynthesis and solubility in sea water (according to Henry's law, the solubility of gas in water decreases with increasing temperature).
An important role in the formation of the planet's climate is played by atmospheric aerosol - solid and liquid particles suspended in the air ranging in size from several nm to tens of microns. There are aerosols of natural and anthropogenic origin. Aerosol is formed in the process of gas-phase reactions from the products of plant vital activity and human economic activity, volcanic eruptions, as a result of dust being lifted by the wind from the surface of the planet, especially from its desert regions, and is also formed from cosmic dust entering the upper atmosphere. Most of the aerosol is concentrated in the troposphere; aerosol from volcanic eruptions forms the so-called Junge layer at an altitude of about 20 km. The largest amount of anthropogenic aerosol enters the atmosphere as a result of the operation of vehicles and thermal power plants, chemical industries, fuel combustion, etc. Therefore, in some areas the composition of the atmosphere differs markedly from ordinary air, which required the creation of a special service for monitoring and controlling the level of atmospheric air pollution.
Atmospheric evolution. The modern atmosphere seems to be of secondary origin: it was formed from gases released by the solid shell of the Earth after the formation of the planet was completed about 4.5 billion years ago. During geological history The Earth's atmosphere underwent significant changes in its composition under the influence of a number of factors: dissipation (volatilization) of gases, mainly lighter ones, into outer space; release of gases from the lithosphere as a result of volcanic activity; chemical reactions between the components of the atmosphere and the rocks that make up the earth's crust; photochemical reactions in the atmosphere itself under the influence of solar UV radiation; accretion (capture) of the matter of the interplanetary medium (for example, meteoric matter). The development of the atmosphere is closely connected with geological and geochemical processes, and for the last 3-4 billion years also with the activity of the biosphere. A significant part of the gases that make up the modern atmosphere (nitrogen, carbon dioxide, water vapor) arose during volcanic activity and intrusion, which carried them out of the depths of the Earth. Oxygen appeared in appreciable quantities about 2 billion years ago as a result of the activity of photosynthetic organisms that originally originated in the surface waters of the ocean.
Based on the data on the chemical composition of carbonate deposits, estimates of the amount of carbon dioxide and oxygen in the atmosphere of the geological past were obtained. During the Phanerozoic (the last 570 million years of the Earth's history), the amount of carbon dioxide in the atmosphere varied widely in accordance with the level of volcanic activity, ocean temperature and photosynthesis. Most At that time, the concentration of carbon dioxide in the atmosphere was significantly higher than today (up to 10 times). The amount of oxygen in the atmosphere of the Phanerozoic changed significantly, and the tendency to increase it prevailed. In the Precambrian atmosphere, the mass of carbon dioxide was, as a rule, greater, and the mass of oxygen, less than in the atmosphere of the Phanerozoic. Fluctuations in the amount of carbon dioxide have had a significant impact on the climate in the past, increasing the greenhouse effect with an increase in the concentration of carbon dioxide, due to which the climate during the main part of the Phanerozoic was much warmer than in the modern era.
atmosphere and life. Without an atmosphere, Earth would be a dead planet. Organic life proceeds in close interaction with the atmosphere and its associated climate and weather. Insignificant in mass compared to the planet as a whole (about a millionth part), the atmosphere is a sine qua non for all life forms. Oxygen, nitrogen, water vapor, carbon dioxide, and ozone are the most important atmospheric gases for the life of organisms. When carbon dioxide is absorbed by photosynthetic plants, organic matter is created that is used as an energy source by the vast majority of living beings, including humans. Oxygen is necessary for the existence of aerobic organisms, for which the energy supply is provided by the oxidation reactions of organic matter. Nitrogen, assimilated by some microorganisms (nitrogen fixers), is necessary for the mineral nutrition of plants. Ozone, which absorbs the Sun's harsh UV radiation, significantly attenuates this life-threatening portion of the sun's radiation. Condensation of water vapor in the atmosphere, the formation of clouds and the subsequent precipitation of precipitation supply water to land, without which no form of life is possible. The vital activity of organisms in the hydrosphere is largely determined by the number and chemical composition atmospheric gases dissolved in water. Since the chemical composition of the atmosphere significantly depends on the activities of organisms, the biosphere and atmosphere can be considered as part of a single system, the maintenance and evolution of which (see Biogeochemical cycles) was of great importance for changing the composition of the atmosphere throughout the history of the Earth as a planet.
Radiation, heat and water balances of the atmosphere. Solar radiation is practically the only source of energy for all physical processes in the atmosphere. main feature radiation regime of the atmosphere - the so-called greenhouse effect: the atmosphere transmits solar radiation to the earth's surface quite well, but actively absorbs the thermal long-wave radiation of the earth's surface, part of which returns to the surface in the form of counter radiation, compensating for the radiative heat loss of the earth's surface (see Atmospheric radiation). In the absence of an atmosphere, the average temperature of the earth's surface would be -18°C, in reality it is 15°C. Incoming solar radiation is partially (about 20%) absorbed into the atmosphere (mainly by water vapor, water droplets, carbon dioxide, ozone and aerosols), and is also scattered (about 7%) by aerosol particles and density fluctuations (Rayleigh scattering). The total radiation, reaching the earth's surface, is partially (about 23%) reflected from it. The reflectance is determined by the reflectivity of the underlying surface, the so-called albedo. On average, the Earth's albedo for the integral solar radiation flux is close to 30%. It varies from a few percent (dry soil and black soil) to 70-90% for freshly fallen snow. The radiative heat exchange between the earth's surface and the atmosphere essentially depends on the albedo and is determined by the effective radiation of the earth's surface and the counter-radiation of the atmosphere absorbed by it. The algebraic sum of radiation fluxes entering the earth's atmosphere from outer space and leaving it back is called the radiation balance.
Transformations of solar radiation after its absorption by the atmosphere and the earth's surface determine the heat balance of the Earth as a planet. The main source of heat for the atmosphere is the earth's surface; heat from it is transferred not only in the form of long-wave radiation, but also by convection, and is also released during the condensation of water vapor. The shares of these heat inflows are on average 20%, 7% and 23%, respectively. About 20% of heat is also added here due to the absorption of direct solar radiation. The flux of solar radiation per unit of time through a single area perpendicular to the sun's rays and located outside the atmosphere at an average distance from the Earth to the Sun (the so-called solar constant) is 1367 W / m 2, the changes are 1-2 W / m 2 depending on cycle of solar activity. With a planetary albedo of about 30%, the time-average global influx of solar energy to the planet is 239 W/m 2 . Since the Earth as a planet emits the same amount of energy into space on average, then, according to the Stefan-Boltzmann law, the effective temperature of the outgoing thermal long-wave radiation is 255 K (-18°C). At the same time, the average temperature of the earth's surface is 15°C. The 33°C difference is due to the greenhouse effect.
The water balance of the atmosphere as a whole corresponds to the equality of the amount of moisture evaporated from the surface of the Earth, the amount of precipitation falling on the earth's surface. The atmosphere over the oceans receives more moisture from evaporation processes than over land, and loses 90% in the form of precipitation. Excess water vapor over the oceans is carried to the continents by air currents. The amount of water vapor transported into the atmosphere from the oceans to the continents is equal to the volume of river flow that flows into the oceans.
air movement. The Earth has a spherical shape, so much less solar radiation comes to its high latitudes than to the tropics. As a result, large temperature contrasts arise between latitudes. The relative position of the oceans and continents also significantly affects the distribution of temperature. Due to the large mass ocean waters and the high heat capacity of water, seasonal fluctuations in ocean surface temperature are much less than those of land. In this regard, in the middle and high latitudes, the air temperature over the oceans is noticeably lower in summer than over the continents, and higher in winter.
Unequal heating of the atmosphere in different areas the globe causes a spatially non-uniform distribution of atmospheric pressure. At sea level, the pressure distribution is characterized by relatively low values near the equator, an increase in the subtropics (high pressure belts), and a decrease in middle and high latitudes. At the same time, over the continents of extratropical latitudes, the pressure is usually increased in winter, and lowered in summer, which is associated with the temperature distribution. Under the action of a pressure gradient, the air experiences an acceleration directed from areas of high pressure to areas of low pressure, which leads to the movement of air masses. The moving air masses are also affected by the deflecting force of the Earth's rotation (the Coriolis force), the friction force, which decreases with height, and in the case of curvilinear trajectories, the centrifugal force. Great importance has turbulent air mixing (see Atmospheric Turbulence).
A complex system of air currents (general circulation of the atmosphere) is associated with the planetary distribution of pressure. In the meridional plane, on average, two or three meridional circulation cells are traced. Near the equator, heated air rises and falls in the subtropics, forming a Hadley cell. The air of the reverse Ferrell cell also descends there. At high latitudes, a direct polar cell is often traced. Meridional circulation velocities are on the order of 1 m/s or less. Due to the action of the Coriolis force, westerly winds are observed in most of the atmosphere with speeds in the middle troposphere of about 15 m/s. There are relatively stable wind systems. These include trade winds - winds blowing from high pressure belts in the subtropics to the equator with a noticeable eastern component (from east to west). Monsoons are quite stable - air currents that have a clearly pronounced seasonal character: they blow from the ocean to the mainland in summer and in the opposite direction in winter. The monsoons of the Indian Ocean are especially regular. In the middle latitudes, movement air masses has a generally western direction (from west to east). This is a zone of atmospheric fronts, on which large eddies arise - cyclones and anticyclones, covering many hundreds and even thousands of kilometers. Cyclones also occur in the tropics; here they differ in smaller sizes, but very high wind speeds, reaching hurricane force (33 m/s or more), the so-called tropical cyclones. In the Atlantic and eastern Pacific they are called hurricanes, and in the western Pacific they are called typhoons. In the upper troposphere and lower stratosphere, in the areas separating the direct cell of the Hadley meridional circulation and the reverse Ferrell cell, relatively narrow, hundreds of kilometers wide, jet streams with sharply defined boundaries are often observed, within which the wind reaches 100-150 and even 200 m/ With.
Climate and weather. The difference in the amount of solar radiation coming at different latitudes to a variety of physical properties the earth's surface, determines the diversity of the Earth's climates. From the equator to tropical latitudes, the air temperature near the earth's surface averages 25-30 ° C and changes little during the year. V equatorial belt there is usually a lot of precipitation, which creates conditions of excessive moisture there. In tropical zones, the amount of precipitation decreases and in some areas becomes very small. Here are the vast deserts of the Earth.
In subtropical and middle latitudes, air temperature varies significantly throughout the year, and the difference between summer and winter temperatures is especially large in areas of the continents remote from the oceans. Thus, in some areas of Eastern Siberia, the annual amplitude of air temperature reaches 65°С. Humidification conditions in these latitudes are very diverse, depend mainly on the regime of the general circulation of the atmosphere, and vary significantly from year to year.
In the polar latitudes, the temperature remains low throughout the year, even if there is a noticeable seasonal variation. This contributes to the widespread distribution of ice cover on the oceans and land and permafrost, occupying over 65% of Russia's area, mainly in Siberia.
Over the past decades, changes in the global climate have become more and more noticeable. The temperature rises more at high latitudes than at low latitudes; more in winter than in summer; more at night than during the day. Over the 20th century, the average annual air temperature near the earth's surface in Russia increased by 1.5-2 ° C, and in some regions of Siberia an increase of several degrees is observed. This is associated with an increase in the greenhouse effect due to an increase in the concentration of small gaseous impurities.
The weather is determined by the conditions of atmospheric circulation and geographic location terrain, it is most stable in the tropics and most variable in middle and high latitudes. Most of all, the weather changes in the zones of change of air masses, due to the passage of atmospheric fronts, cyclones and anticyclones, carrying precipitation and increasing wind. Data for weather forecasting is collected from ground-based weather stations, ships and aircraft, and meteorological satellites. See also meteorology.
Optical, acoustic and electrical phenomena in the atmosphere. When spread electromagnetic radiation in the atmosphere, as a result of refraction, absorption and scattering of light by air and various particles (aerosol, ice crystals, water drops), various optical phenomena arise: rainbow, crowns, halo, mirage, etc. Scattering of light determines the apparent height of the firmament and the blue color of the sky. The visibility range of objects is determined by the conditions of light propagation in the atmosphere (see Atmospheric visibility). The transparency of the atmosphere at different wavelengths determines the communication range and the possibility of detecting objects with instruments, including the possibility of astronomical observations from the Earth's surface. For studies of optical inhomogeneities in the stratosphere and mesosphere, the phenomenon of twilight plays an important role. For example, photographing twilight from spacecraft makes it possible to detect aerosol layers. Features of the propagation of electromagnetic radiation in the atmosphere determine the accuracy of methods for remote sensing of its parameters. All these questions, like many others, are studied by atmospheric optics. Refraction and scattering of radio waves determine the possibilities of radio reception (see Propagation of radio waves).
The propagation of sound in the atmosphere depends on the spatial distribution of temperature and wind speed (see Atmospheric acoustics). It is of interest for remote sensing of the atmosphere. Explosions of charges launched by rockets into the upper atmosphere provided a wealth of information about wind systems and the course of temperature in the stratosphere and mesosphere. In a stably stratified atmosphere, when the temperature falls with height more slowly than the adiabatic gradient (9.8 K/km), so-called internal waves arise. These waves can propagate upward into the stratosphere and even into the mesosphere, where they attenuate, contributing to increased wind and turbulence.
The negative charge of the Earth and the electric field caused by it, the atmosphere, together with the electrically charged ionosphere and magnetosphere, create a global electrical circuit. An important role is played by the formation of clouds and lightning electricity. The danger of lightning discharges necessitated the development of methods for lightning protection of buildings, structures, power lines and communications. This phenomenon is of particular danger to aviation. Lightning discharges cause atmospheric radio interference, called atmospherics (see Whistling atmospherics). During a sharp increase in the strength of the electric field, luminous discharges are observed that arise on the points and sharp corners of objects protruding above the earth's surface, on individual peaks in the mountains, etc. (Elma lights). The atmosphere always contains a strongly varying number of light and heavy ions, depending on the specific conditions, which determine the electrical conductivity of the atmosphere. The main air ionizers near the earth's surface are the radiation of radioactive substances contained in the earth's crust and in the atmosphere, as well as cosmic rays. See also atmospheric electricity.
Human influence on the atmosphere. Over the past centuries, there has been an increase in the concentration of greenhouse gases in the atmosphere due to human activities. The percentage of carbon dioxide increased from 2.8-10 2 two hundred years ago to 3.8-10 2 in 2005, the content of methane - from 0.7-10 1 about 300-400 years ago to 1.8-10 -4 at the beginning of the 21st century; about 20% of the increase in the greenhouse effect over the past century was given by freons, which practically did not exist in the atmosphere until the middle of the 20th century. These substances are recognized as stratospheric ozone depleters and their production is prohibited by the 1987 Montreal Protocol. The increase in carbon dioxide concentration in the atmosphere is caused by the burning of ever-increasing amounts of coal, oil, gas and other carbon fuels, as well as the deforestation, which reduces the absorption of carbon dioxide through photosynthesis. The concentration of methane increases with the growth of oil and gas production (due to its losses), as well as with the expansion of rice crops and an increase in the number of cattle. All this contributes to climate warming.
To change the weather, methods of active influence on atmospheric processes have been developed. They are used to protect agricultural plants from hail damage by dispersing special reagents in thunderclouds. There are also methods for dispelling fog at airports, protecting plants from frost, influencing clouds to increase rainfall in the right places, or to disperse clouds at times of mass events.
Study of the atmosphere. Information about the physical processes in the atmosphere is obtained primarily from meteorological observations, which are carried out by a global network of permanent meteorological stations and posts located on all continents and on many islands. Daily observations provide information about the temperature and humidity of the air, atmospheric pressure and precipitation, cloudiness, wind, etc. Observations of solar radiation and its transformations are carried out at actinometric stations. Of great importance for the study of the atmosphere are the networks of aerological stations, where meteorological measurements are made with the help of radiosondes up to a height of 30-35 km. At a number of stations, observations are made of atmospheric ozone, electrical phenomena in the atmosphere, and the chemical composition of the air.
Data from ground stations are supplemented by observations on the oceans, where "weather ships" operate, permanently located in certain areas of the World Ocean, as well as meteorological information received from research and other ships.
In recent decades, an increasing amount of information about the atmosphere has been obtained with the help of meteorological satellites, which are equipped with instruments for photographing clouds and measuring the fluxes of ultraviolet, infrared, and microwave radiation from the Sun. Satellites make it possible to obtain information about vertical temperature profiles, cloudiness and its water content, elements of the atmospheric radiation balance, ocean surface temperature, etc. Using measurements of the refraction of radio signals from a system of navigation satellites, it is possible to determine vertical profiles of density, pressure and temperature, as well as moisture content in the atmosphere . With the help of satellites, it became possible to clarify the value of the solar constant and the planetary albedo of the Earth, build maps of the radiation balance of the Earth-atmosphere system, measure the content and variability of small atmospheric impurities, solve many other problems of atmospheric physics and monitoring environment.
Lit .: Budyko M. I. Climate in the past and future. L., 1980; Matveev L. T. Course of general meteorology. Physics of the atmosphere. 2nd ed. L., 1984; Budyko M. I., Ronov A. B., Yanshin A. L. History of the atmosphere. L., 1985; Khrgian A.Kh. Atmospheric Physics. M., 1986; Atmosphere: A Handbook. L., 1991; Khromov S. P., Petrosyants M. A. Meteorology and climatology. 5th ed. M., 2001.
G. S. Golitsyn, N. A. Zaitseva.
Earth's atmosphere is the gaseous envelope of our planet. Its lower boundary passes at the level of the earth's crust and hydrosphere, and the upper one passes into the near-Earth region of outer space. The atmosphere contains about 78% nitrogen, 20% oxygen, up to 1% argon, carbon dioxide, hydrogen, helium, neon and some other gases.
This earth shell is characterized by clearly defined layering. The layers of the atmosphere are determined by the vertical distribution of temperature and the different density of gases at its different levels. There are such layers of the Earth's atmosphere: troposphere, stratosphere, mesosphere, thermosphere, exosphere. The ionosphere is distinguished separately.
Up to 80% of the total mass of the atmosphere is the troposphere - the lower surface layer of the atmosphere. The troposphere in the polar zones is located at a level of up to 8-10 km above the earth's surface, in the tropical zone - up to a maximum of 16-18 km. Between the troposphere and the overlying stratosphere is the tropopause - the transition layer. In the troposphere, temperature decreases as altitude increases, and atmospheric pressure decreases with altitude. The average temperature gradient in the troposphere is 0.6°C per 100 m. The temperature at different levels of this shell is determined by the absorption of solar radiation and the efficiency of convection. Almost all human activity takes place in the troposphere. The highest mountains do not go beyond the troposphere, only air transport can cross the upper boundary of this shell to a small height and be in the stratosphere. A large proportion of water vapor is contained in the troposphere, which determines the formation of almost all clouds. Also, almost all aerosols (dust, smoke, etc.) that form on the earth's surface are concentrated in the troposphere. In the boundary lower layer of the troposphere, daily fluctuations in temperature and air humidity are expressed, the wind speed is usually reduced (it increases with altitude). In the troposphere, there is a variable division of the air column into air masses in the horizontal direction, which differ in a number of characteristics depending on the zone and the area of their formation. At atmospheric fronts - the boundaries between air masses - cyclones and anticyclones are formed, which determine the weather in a certain area for a specific period of time.
The stratosphere is the layer of the atmosphere between the troposphere and the mesosphere. The limits of this layer range from 8-16 km to 50-55 km above the Earth's surface. In the stratosphere, the gas composition of air is approximately the same as in the troposphere. A distinctive feature is a decrease in the concentration of water vapor and an increase in the ozone content. The ozone layer of the atmosphere, which protects the biosphere from the aggressive effects of ultraviolet light, is at a level of 20 to 30 km. In the stratosphere, the temperature rises with height, and temperature value are determined by solar radiation, and not by convection (movements of air masses), as in the troposphere. The heating of the air in the stratosphere is due to the absorption of ultraviolet radiation by ozone.
The mesosphere extends above the stratosphere up to a level of 80 km. This layer of the atmosphere is characterized by the fact that the temperature decreases from 0 ° C to - 90 ° C as the height increases. This is the coldest region of the atmosphere.
Above the mesosphere is the thermosphere up to a level of 500 km. From the border with the mesosphere to the exosphere, the temperature varies from about 200 K to 2000 K. Up to a level of 500 km, the air density decreases by several hundred thousand times. The relative composition of the atmospheric components of the thermosphere is similar to the surface layer of the troposphere, but with increasing altitude, more oxygen passes into the atomic state. A certain proportion of molecules and atoms of the thermosphere is in an ionized state and distributed in several layers, they are united by the concept of the ionosphere. The characteristics of the thermosphere vary over a wide range depending on the geographic latitude, the amount of solar radiation, the time of year and day.
The upper layer of the atmosphere is the exosphere. This is the thinnest layer of the atmosphere. In the exosphere, the mean free paths of particles are so huge that particles can freely escape into interplanetary space. The mass of the exosphere is one ten millionth of the total mass of the atmosphere. The lower boundary of the exosphere is the level of 450-800 km, and the upper boundary is the area where the concentration of particles is the same as in outer space, - several thousand kilometers from the Earth's surface. The exosphere is made up of plasma, an ionized gas. Also in the exosphere are radiation belts our planet.
Video presentation - layers of the Earth's atmosphere:
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Its upper limit is at an altitude of 8-10 km in polar, 10-12 km in temperate and 16-18 km in tropical latitudes; lower in winter than in summer. The lower, main layer of the atmosphere. It contains more than 80% of the total mass of atmospheric air and about 90% of all water vapor present in the atmosphere. Turbulence and convection are strongly developed in the troposphere, clouds appear, cyclones and anticyclones develop. Temperature decreases with altitude with an average vertical gradient of 0.65°/100 m
For "normal conditions" at the Earth's surface are taken: density 1.2 kg/m3, barometric pressure 101.35 kPa, temperature plus 20 °C and relative humidity 50%. These conditional indicators have a purely engineering value.
Stratosphere
The layer of the atmosphere located at an altitude of 11 to 50 km. A slight change in temperature in the 11-25 km layer (lower layer of the stratosphere) and its increase in the 25-40 km layer from −56.5 to 0.8 ° (upper stratosphere or inversion region) are typical. Having reached a value of about 273 K (almost 0 ° C) at an altitude of about 40 km, the temperature remains constant up to an altitude of about 55 km. This region of constant temperature is called the stratopause and is the boundary between the stratosphere and the mesosphere.
Stratopause
The boundary layer of the atmosphere between the stratosphere and the mesosphere. There is a maximum in the vertical temperature distribution (about 0 °C).
Mesosphere
mesopause
Transitional layer between mesosphere and thermosphere. There is a minimum in the vertical temperature distribution (about -90°C).
Karman Line
Altitude above sea level, which is conventionally accepted as the boundary between the Earth's atmosphere and space.
Thermosphere
The upper limit is about 800 km. The temperature rises to altitudes of 200-300 km, where it reaches values of the order of 1500 K, after which it remains almost constant up to high altitudes. Under the influence of ultraviolet and x-ray solar radiation and cosmic radiation, air is ionized ("polar lights") - the main regions of the ionosphere lie inside the thermosphere. At altitudes above 300 km, atomic oxygen predominates.
Exosphere (scattering sphere)
Up to a height of 100 km, the atmosphere is a homogeneous, well-mixed mixture of gases. In higher layers, the distribution of gases in height depends on their molecular masses, the concentration of heavier gases decreases faster with distance from the Earth's surface. Due to the decrease in gas density, the temperature drops from 0 °C in the stratosphere to -110 °C in the mesosphere. However, the kinetic energy of individual particles at altitudes of 200–250 km corresponds to a temperature of ~1500°C. Above 200 km, significant fluctuations in temperature and gas density are observed in time and space.
At an altitude of about 2000-3000 km, the exosphere gradually passes into the so-called near space vacuum, which is filled with highly rarefied particles of interplanetary gas, mainly hydrogen atoms. But this gas is only part of the interplanetary matter. The other part is composed of dust-like particles of cometary and meteoric origin. In addition to extremely rarefied dust-like particles, electromagnetic and corpuscular radiation of solar and galactic origin penetrates into this space.
The troposphere accounts for about 80% of the mass of the atmosphere, the stratosphere accounts for about 20%; the mass of the mesosphere is no more than 0.3%, the thermosphere is less than 0.05% of the total mass of the atmosphere. Based on the electrical properties in the atmosphere, the neutrosphere and ionosphere are distinguished. It is currently believed that the atmosphere extends to an altitude of 2000-3000 km.
Depending on the composition of the gas in the atmosphere, they emit homosphere and heterosphere. heterosphere- this is an area where gravity affects the separation of gases, since their mixing at such a height is negligible. Hence follows the variable composition of the heterosphere. Below it lies a well-mixed, homogeneous part of the atmosphere, called the homosphere. The boundary between these layers is called turbopause, it lies at an altitude of about 120 km.
Physical Properties
The thickness of the atmosphere is approximately 2000 - 3000 km from the Earth's surface. The total mass of air - (5.1-5.3)? 10 18 kg. The molar mass of clean dry air is 28.966. Pressure at 0 °C at sea level 101.325 kPa; critical temperature ?140.7 °C; critical pressure 3.7 MPa; C p 1.0048?10? J / (kg K) (at 0 °C), C v 0.7159 10? J/(kg K) (at 0 °C). Solubility of air in water at 0°С - 0.036%, at 25°С - 0.22%.
Physiological and other properties of the atmosphere
Already at an altitude of 5 km above sea level, an untrained person develops oxygen starvation and, without adaptation, a person's performance is significantly reduced. This is where the physiological zone of the atmosphere ends. Human breathing becomes impossible at an altitude of 15 km, although up to about 115 km the atmosphere contains oxygen.
The atmosphere provides us with the oxygen we need to breathe. However, due to the decrease in the total pressure of the atmosphere, as one rises to a height, the partial pressure of oxygen also decreases accordingly.
The human lungs constantly contain about 3 liters of alveolar air. The partial pressure of oxygen in the alveolar air at normal atmospheric pressure is 110 mm Hg. Art., pressure of carbon dioxide - 40 mm Hg. Art., and water vapor - 47 mm Hg. Art. With increasing altitude, the oxygen pressure drops, and the total pressure of water vapor and carbon dioxide in the lungs remains almost constant - about 87 mm Hg. Art. The flow of oxygen into the lungs will completely stop when the pressure of the surrounding air becomes equal to this value.
At an altitude of about 19-20 km, the atmospheric pressure drops to 47 mm Hg. Art. Therefore, at this height, water and interstitial fluid begin to boil in the human body. Outside the pressurized cabin at these altitudes, death occurs almost instantly. Thus, from the point of view of human physiology, "space" begins already at an altitude of 15-19 km.
The dense layers of air - the troposphere and stratosphere - protect us from damaging effect radiation. With sufficient rarefaction of air, at altitudes of more than 36 km, ionizing radiation, primary cosmic rays, has an intense effect on the body; at altitudes of more than 40 km, the ultraviolet part of the solar spectrum, which is dangerous for humans, operates.
As we rise to an ever greater height above the Earth's surface, gradually weaken, and then completely disappear, such phenomena that are familiar to us observed in the lower layers of the atmosphere, such as the propagation of sound, the occurrence of aerodynamic lift and resistance, heat transfer by convection, etc.
In rarefied layers of air, the propagation of sound is impossible. Up to altitudes of 60-90 km, it is still possible to use air resistance and lift for controlled aerodynamic flight. But starting from altitudes of 100-130 km, the concepts of the M number and the sound barrier familiar to every pilot lose their meaning, there passes the conditional Karman Line, beyond which the sphere of purely ballistic flight begins, which can only be controlled using reactive forces.
At altitudes above 100 km, the atmosphere is also deprived of another remarkable property - the ability to absorb, conduct and transfer thermal energy by convection (i.e., by means of air mixing). This means that various elements of equipment, equipment of the orbital space station will not be able to be cooled from the outside in the way it is usually done on an airplane - with the help of air jets and air radiators. At such a height, as in space in general, the only way to transfer heat is thermal radiation.
Composition of the atmosphere
The Earth's atmosphere consists mainly of gases and various impurities (dust, water drops, ice crystals, sea salts, combustion products).
The concentration of gases that make up the atmosphere is almost constant, with the exception of water (H 2 O) and carbon dioxide (CO 2).
| Gas | Content by volume, % |
Content by weight, % |
|---|---|---|
| Nitrogen | 78,084 | 75,50 |
| Oxygen | 20,946 | 23,10 |
| Argon | 0,932 | 1,286 |
| Water | 0,5-4 | - |
| Carbon dioxide | 0,032 | 0,046 |
| Neon | 1.818×10 −3 | 1.3×10 −3 |
| Helium | 4.6×10 −4 | 7.2×10 −5 |
| Methane | 1.7×10 −4 | - |
| Krypton | 1.14×10 −4 | 2.9×10 −4 |
| Hydrogen | 5×10 −5 | 7.6×10 −5 |
| Xenon | 8.7×10 −6 | - |
| Nitrous oxide | 5×10 −5 | 7.7×10 −5 |
In addition to the gases indicated in the table, the atmosphere contains SO 2, NH 3, CO, ozone, hydrocarbons, HCl, vapors, I 2, and many other gases in small quantities. In the troposphere there is constantly a large amount of suspended solid and liquid particles (aerosol).
History of the formation of the atmosphere
According to the most common theory, the Earth's atmosphere has been in four different compositions over time. Initially, it consisted of light gases (hydrogen and helium) captured from interplanetary space. This so-called primary atmosphere(about four billion years ago). At the next stage, active volcanic activity led to the saturation of the atmosphere with gases other than hydrogen (carbon dioxide, ammonia, water vapor). This is how secondary atmosphere(about three billion years before our days). This atmosphere was restorative. Further, the process of formation of the atmosphere was determined by the following factors:
- leakage of light gases (hydrogen and helium) into interplanetary space;
- chemical reactions occurring in the atmosphere under the influence of ultraviolet radiation, lightning discharges and some other factors.
Gradually, these factors led to the formation tertiary atmosphere, characterized by a much lower content of hydrogen and a much higher content of nitrogen and carbon dioxide (formed as a result of chemical reactions from ammonia and hydrocarbons).
Nitrogen
Education a large number N 2 is due to the oxidation of the ammonia-hydrogen atmosphere by molecular O 2, which began to come from the surface of the planet as a result of photosynthesis, starting from 3 billion years ago. N 2 is also released into the atmosphere as a result of the denitrification of nitrates and other nitrogen-containing compounds. Nitrogen is oxidized by ozone to NO in the upper atmosphere.
Nitrogen N 2 enters into reactions only under specific conditions (for example, during a lightning discharge). Oxidation of molecular nitrogen by ozone during electrical discharges is used in the industrial production of nitrogen fertilizers. It can be oxidized with low energy consumption and converted into a biologically active form by cyanobacteria (blue-green algae) and nodule bacteria that form rhizobial symbiosis with legumes, the so-called. green manure.
Oxygen
The composition of the atmosphere began to change radically with the advent of living organisms on Earth, as a result of photosynthesis, accompanied by the release of oxygen and the absorption of carbon dioxide. Initially, oxygen was spent on the oxidation of reduced compounds - ammonia, hydrocarbons, the ferrous form of iron contained in the oceans, etc. At the end of this stage, the oxygen content in the atmosphere began to grow. Gradually, a modern atmosphere with oxidizing properties formed. Since this caused serious and abrupt changes in many processes occurring in the atmosphere, lithosphere and biosphere, this event was called the Oxygen Catastrophe.
Carbon dioxide
The content of CO 2 in the atmosphere depends on volcanic activity and chemical processes in the earth's shells, but most of all - on the intensity of biosynthesis and decomposition of organic matter in the Earth's biosphere. Almost the entire current biomass of the planet (about 2.4 × 10 12 tons) is formed due to carbon dioxide, nitrogen and water vapor contained in the atmospheric air. Buried in the ocean , swamps and forests , organic matter turns into coal , oil and natural gas . (see Geochemical carbon cycle)
noble gases
Air pollution
Recently, man has begun to influence the evolution of the atmosphere. The result of his activities was a constant significant increase in the content of carbon dioxide in the atmosphere due to the combustion of hydrocarbon fuels accumulated in previous geological epochs. Huge amounts of CO 2 are consumed during photosynthesis and absorbed by the world's oceans. This gas enters the atmosphere due to the decomposition of carbonate rocks and organic substances of plant and animal origin, as well as due to volcanism and human production activities. Over the past 100 years, the content of CO 2 in the atmosphere has increased by 10%, with the main part (360 billion tons) coming from fuel combustion. If the growth rate of fuel combustion continues, then in the next 50 - 60 years the amount of CO 2 in the atmosphere will double and may lead to global climate change.
Fuel combustion is the main source of polluting gases (СО,, SO 2). Sulfur dioxide is oxidized by atmospheric oxygen to SO 3 in the upper atmosphere, which in turn interacts with water vapor and ammonia, and the resulting sulfuric acid (H 2 SO 4) and ammonium sulfate ((NH 4) 2 SO 4) return to the surface of the Earth in the form of a so-called. acid rain. The use of internal combustion engines leads to significant air pollution with nitrogen oxides, hydrocarbons and lead compounds (tetraethyl lead Pb (CH 3 CH 2) 4)).
Aerosol pollution of the atmosphere is caused both by natural causes (volcanic eruption, dust storms, entrainment of sea water droplets and plant pollen, etc.) and by human economic activity (mining of ores and building materials, fuel combustion, cement production, etc.). Intense large-scale removal of solid particles into the atmosphere is one of the possible causes of climate change on the planet.
Literature
- V. V. Parin, F. P. Kosmolinsky, B. A. Dushkov "Space biology and medicine" (2nd edition, revised and enlarged), M.: "Prosveshchenie", 1975, 223 pages.
- N. V. Gusakova "Environmental Chemistry", Rostov-on-Don: Phoenix, 2004, 192 s ISBN 5-222-05386-5
- Sokolov V. A. Geochemistry of natural gases, M., 1971;
- McEwen M., Phillips L.. Atmospheric Chemistry, M., 1978;
- Wark K., Warner S., Air pollution. Sources and control, trans. from English, M.. 1980;
- Monitoring of background pollution of natural environments. v. 1, L., 1982.
see also
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