The oxygen content in the surface layer of the atmosphere is. Geography theme - atmosphere
Composition of the Earth. Air
Air is a mechanical mixture of various gases that make up the Earth's atmosphere. Air is necessary for the respiration of living organisms and is widely used in industry.
The fact that air is a mixture, and not a homogeneous substance, was proven 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” is released, that is, carbon dioxide, and burnt magnesia (magnesium oxide) is formed. When burning limestone, on the contrary, “bound air” is removed. Based on these experiments, the scientist concluded that the difference between carbon dioxide and caustic alkalis is that the former contains carbon dioxide, which is one of the constituents of 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 an altitude 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 turbo pause.
The chemical reaction in which molecules are decomposed into atoms under the influence of solar and cosmic radiation is called photodissociation. The decay of molecular oxygen produces atomic oxygen, 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 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 by molecular oxygen, which is formed during photosynthesis. Currently, small amounts of nitrogen enter the atmosphere as a result of denitrification - the process of reducing 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 layers of the 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 and provides mineral nutrition to plants. It determines the rate of biochemical reactions and plays the role of an oxygen diluent.
The second most common gas in the Earth's atmosphere is oxygen. 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 same ultraviolet radiation, ozone decomposes:
O 3 + hν → O 2 + O
О 3 + O → 2О 2
As a result of the first reaction, atomic oxygen is formed, and as a result of the second, molecular oxygen is formed. All 4 reactions are called the “Chapman mechanism”, named after the British scientist Sidney Chapman who discovered them in 1930.
Oxygen is used for respiration of living organisms. With its help, oxidation and combustion processes 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 in 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 the helium nucleus, which in During the process of energy loss, it 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 transuranic elements with a phenomenally short half-life or came from space, where the krypton content is ten million times higher than on Earth.
Xenon is the result of the fission of uranium, but the bulk of this gas remains from the early stages of the formation of the Earth, from the primordial atmosphere.
Carbon dioxide enters the atmosphere as a result of volcanic eruptions and during the decomposition of organic matter. Its content in the atmosphere of the Earth's mid-latitudes 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 associated 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 evaporates 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, the troposphere, there is always a large amount of suspended solid and liquid particles.
Sources of particulate matter in the Earth's atmosphere include volcanic eruptions, pollen, microorganisms, and, more recently, human activities, such as the burning of fossil fuels during production. The smallest particles of dust, which are condensation nuclei, cause the formation of fogs and clouds. Without particulate matter constantly present in the atmosphere, precipitation would not fall on Earth.
At sea level 1013.25 hPa (about 760 mmHg). The global average air temperature at the Earth's surface is 15°C, with temperatures varying from approximately 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 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 located in the troposphere. Above the troposphere is the stratosphere, a layer generally characterized by an increase in temperature with height. The transition layer between the troposphere and stratosphere is called the tropopause. In the lower stratosphere, down to a level of about 20 km, the temperature changes little with height (the so-called isothermal region) and often even decreases slightly. Above that, the temperature increases due to the absorption of UV radiation from the Sun 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 again drops 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. Above the mesopause, the thermosphere begins - a layer characterized by a rapid increase in temperature, reaching 800-1200 K at an altitude of 250 km. In the thermosphere, corpuscular and X-ray radiation from the Sun is absorbed, meteors are slowed down and burned, so it acts as a protective layer of the Earth. Even higher is the exosphere, from where atmospheric gases are dispersed into outer space due to dissipation and where a gradual transition from the atmosphere to interplanetary space occurs.
Atmospheric composition. Up to an altitude of about 100 km, the atmosphere is almost homogeneous in chemical composition and the average molecular weight of the air (about 29) is constant. 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 permanent 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 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 their low content, their role in atmospheric processes is very significant.
Above 100-110 km, dissociation of molecules of oxygen, carbon dioxide and water vapor occurs, so the molecular mass 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 at the earth's surface from 2.6% in the tropics to 0.2% in polar latitudes. It falls quickly with height, decreasing by half already at an altitude of 1.5-2 km. The vertical column of the atmosphere at temperate latitudes contains about 1.7 cm of “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, concentrated 90% 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 in the range from 0.22 to 0.45 cm (the thickness of the ozone layer at pressure p = 1 atm and temperature T = 0°C). In ozone holes observed in the spring in Antarctica since the early 1980s, ozone content can drop to 0.07 cm. It increases from the equator to the poles and has an annual cycle with a maximum in spring and a minimum in autumn, and the amplitude of the annual cycle is small in the tropics and grows towards high latitudes. A significant 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 shaping 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 life and human economic activity, volcanic eruptions, as a result of dust rising by the wind from the surface of the planet, especially from its desert regions, and is also formed from cosmic dust falling into the upper layers of the 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 production, fuel combustion, etc. Therefore, in some areas the composition of the atmosphere is noticeably different from ordinary air, which required the creation of a special service for observing and monitoring the level of atmospheric air pollution.
Evolution of the atmosphere. The modern atmosphere is apparently 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 the geological history of the Earth, the atmosphere has undergone 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 matter from the interplanetary medium (for example, meteoric matter). The development of the atmosphere is closely related to geological and geochemical processes, and over the last 3-4 billion years also to 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 from the depths of the Earth. Oxygen appeared in appreciable quantities about 2 billion years ago as a result of photosynthetic organisms that originally arose in the surface waters of the ocean.
Based on 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. Throughout the Phanerozoic (the last 570 million years of Earth's history), the amount of carbon dioxide in the atmosphere varied widely depending on the level of volcanic activity, ocean temperature and the rate of photosynthesis. For most of this time, the concentration of carbon dioxide in the atmosphere was significantly higher than today (up to 10 times). The amount of oxygen in the Phanerozoic atmosphere changed significantly, with a prevailing trend towards its increase. In the Precambrian atmosphere, the mass of carbon dioxide was, as a rule, greater, and the mass of oxygen was smaller compared to the Phanerozoic atmosphere. Fluctuations in the amount of carbon dioxide had a significant impact on the climate in the past, increasing the greenhouse effect with increasing concentrations of carbon dioxide, making the climate much warmer throughout the main part of the Phanerozoic compared to the modern era.
Atmosphere and life. Without an atmosphere, the Earth would be a dead planet. Organic life occurs in close interaction with the atmosphere and the associated climate and weather. Insignificant in mass compared to the planet as a whole (about a part in a million), the atmosphere is an indispensable condition for all forms of life. The most important of the atmospheric gases for the life of organisms are oxygen, nitrogen, water vapor, carbon dioxide, and ozone. When carbon dioxide is absorbed by photosynthetic plants, organic matter is created, which is used as a source of energy by the vast majority of living beings, including humans. Oxygen is necessary for the existence of aerobic organisms, for which the flow of energy is provided by oxidation reactions of organic matter. Nitrogen, assimilated by some microorganisms (nitrogen fixers), is necessary for the mineral nutrition of plants. Ozone, which absorbs hard UV radiation from the Sun, significantly weakens this part of solar radiation harmful to life. The condensation of water vapor in the atmosphere, the formation of clouds and subsequent 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 amount and chemical composition of 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. The main feature of the radiation regime of the atmosphere is the so-called greenhouse effect: the atmosphere transmits solar radiation to the earth's surface quite well, but actively absorbs thermal long-wave radiation from the earth's surface, part of which returns to the surface in the form of counter radiation, compensating for radiative heat loss from 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, but 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 coefficient is determined by the reflectivity of the underlying surface, the so-called albedo. On average, the Earth's albedo for the integral flux of solar radiation is close to 30%. It varies from a few percent (dry soil and black soil) to 70-90% for freshly fallen snow. Radiative heat exchange between the earth's surface and the atmosphere significantly depends on 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 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 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 equal to 1367 W/m2, changes are 1-2 W/m2 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/m2. Since the Earth as a planet emits on average the same amount of energy into space, 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 difference of 33°C is due to the greenhouse effect.
The water balance of the atmosphere generally corresponds to the equality of the amount of moisture evaporated from the Earth's surface and 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 transported to the continents by air currents. The amount of water vapor transferred into the atmosphere from the oceans to the continents is equal to the volume of the rivers flowing into the oceans.
Air movement. The Earth is spherical, so much less solar radiation reaches its high latitudes than the tropics. As a result, large temperature contrasts arise between latitudes. The temperature distribution is also significantly affected by the relative positions of the oceans and continents. Due to the large mass of ocean waters and the high heat capacity of water, seasonal fluctuations in ocean surface temperature are much less than on land. In this regard, in the middle and high latitudes, the air temperature over the oceans in summer is noticeably lower than over the continents, and higher in winter.
Uneven heating of the atmosphere in different regions of the globe causes a spatially inhomogeneous distribution of atmospheric pressure. At sea level, the pressure distribution is characterized by relatively low values near the equator, increases in the subtropics (high pressure belts) and decreases in the middle and high latitudes. At the same time, over the continents of extratropical latitudes, the pressure is usually increased in winter and decreased in summer, which is associated with the temperature distribution. Under the influence of a pressure gradient, air experiences acceleration directed from areas of high pressure to areas of low pressure, which leads to the movement of air masses. Moving air masses are also affected by the deflecting force of the Earth's rotation (Coriolis force), the friction force, which decreases with height, and, for curved trajectories, the centrifugal force. Turbulent mixing of air is of great importance (see Turbulence in the atmosphere).
A complex system of air currents (general atmospheric circulation) is associated with the planetary pressure distribution. In the meridional plane, on average, two or three meridional circulation cells can be 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 straight polar cell is often visible. Meridional circulation velocities are on the order of 1 m/s or less. Due to 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 zones in the subtropics to the equator with a noticeable eastern component (from east to west). Monsoons are fairly stable - air currents that have a clearly defined seasonal character: they blow from the ocean to the mainland in the summer and in the opposite direction in the winter. The Indian Ocean monsoons are especially regular. In mid-latitudes, the movement of air masses is mainly westerly (from west to east). This is a zone of atmospheric fronts on which large vortices arise - cyclones and anticyclones, covering many hundreds and even thousands of kilometers. Cyclones also occur in the tropics; here they are distinguished by their 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 Oceans they are called hurricanes, and in the western Pacific Ocean they are called typhoons. In the upper troposphere and lower stratosphere, in the areas separating the direct Hadley meridional circulation cell 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 arriving at different latitudes to the earth's surface, which is varied in its physical properties, determines the diversity of the Earth's climates. From the equator to tropical latitudes, the air temperature at the earth's surface averages 25-30°C and varies little throughout the year. In the equatorial belt, there is usually a lot of precipitation, which creates conditions of excess moisture there. In tropical zones, precipitation decreases and in some areas becomes very low. 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 far from the oceans. Thus, in some areas of Eastern Siberia, the annual air temperature range reaches 65°C. Humidification conditions in these latitudes are very diverse, depend mainly on the regime of general atmospheric circulation and vary significantly from year to year.
In 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, which occupy over 65% of its area in Russia, mainly in Siberia.
Over the past decades, changes in the global climate have become increasingly noticeable. Temperatures rise 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 at the earth's surface in Russia increased by 1.5-2°C, and in some areas of Siberia an increase of several degrees was observed. This is associated with an increase in the greenhouse effect due to an increase in the concentration of trace gases.
The weather is determined by the conditions of atmospheric circulation and the geographical location of the area; it is most stable in the tropics and most variable in the middle and high latitudes. The weather changes most of all in zones of changing air masses caused by the passage of atmospheric fronts, cyclones and anticyclones carrying precipitation and increased wind. Data for weather forecasting are collected at ground-based weather stations, ships and aircraft, and from meteorological satellites. See also Meteorology.
Optical, acoustic and electrical phenomena in the atmosphere. When electromagnetic radiation propagates 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: rainbows, crowns, halo, mirage, etc. The scattering of light determines the apparent height of the vault of heaven and 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 ability to detect objects with instruments, including the possibility of astronomical observations from the Earth’s surface. For studies of optical inhomogeneities of the stratosphere and mesosphere, the twilight phenomenon 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, as well as 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 atmospheric sensing by remote methods. Explosions of charges launched by rockets into the upper atmosphere provided rich information about wind systems and temperature variations in the stratosphere and mesosphere. In a stably stratified atmosphere, when the temperature decreases with height slower 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 winds and turbulence.
The negative charge of the Earth and the resulting electric field, the atmosphere, together with the electrically charged ionosphere and magnetosphere, create a global electrical circuit. The formation of clouds and thunderstorm electricity plays an important role in this. The danger of lightning discharges has necessitated the development of lightning protection methods for buildings, structures, power lines and communications. This phenomenon poses a particular danger to aviation. Lightning discharges cause atmospheric radio interference, called atmospherics (see Whistling atmospherics). During a sharp increase in the electric field strength, luminous discharges are observed that appear on the tips 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 greatly varying amount of light and heavy ions, depending on specific conditions, which determine the electrical conductivity of the atmosphere. The main ionizers of air near the earth's surface are radiation from radioactive substances contained in the earth's crust and 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 economic activities. The percentage of carbon dioxide increased from 2.8-10 2 two hundred years ago to 3.8-10 2 in 2005, the methane content - from 0.7-10 1 approximately 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 last century came from freons, which were practically absent in the atmosphere until the mid-20th century. These substances are recognized as stratospheric ozone depleters, and their production is prohibited by the 1987 Montreal Protocol. The increase in the concentration of carbon dioxide in the atmosphere is caused by the burning of ever-increasing amounts of coal, oil, gas and other types of carbon fuels, as well as the clearing of forests, as a result of which the absorption of carbon dioxide through photosynthesis decreases. The concentration of methane increases with an increase in 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 have been developed to actively influence atmospheric processes. They are used to protect agricultural plants from hail by dispersing special reagents in thunderclouds. There are also methods for dispersing fog at airports, protecting plants from frost, influencing clouds to increase precipitation in desired areas, or for dispersing clouds during public events.
Study of the atmosphere. Information about physical processes in the atmosphere is obtained primarily from meteorological observations, which are carried out by a global network of permanently operating meteorological stations and posts located on all continents and on many islands. Daily observations provide information about air temperature and humidity, atmospheric pressure and precipitation, cloudiness, wind, etc. Observations of solar radiation and its transformations are carried out at actinometric stations. Of great importance for studying the atmosphere are networks of aerological stations, at which meteorological measurements are carried out up to an altitude of 30-35 km using radiosondes. At a number of stations, observations of atmospheric ozone, electrical phenomena in the atmosphere, and the chemical composition of the air are carried out.
Data from ground stations are supplemented by observations on the oceans, where “weather ships” operate, constantly 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 using meteorological satellites, which carry instruments for photographing clouds and measuring fluxes of ultraviolet, infrared and microwave radiation from the Sun. Satellites make it possible to obtain information about vertical profiles of temperature, cloudiness and its water supply, elements of the radiation balance of the atmosphere, 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 has become possible to clarify the value of the solar constant and planetary albedo of the Earth, build maps of the radiation balance of the Earth-atmosphere system, measure the content and variability of small atmospheric pollutants, and solve many other problems of atmospheric physics and environmental monitoring.
Lit.: Budyko M.I. Climate in the past and future. L., 1980; Matveev L. T. Course of general meteorology. Atmospheric physics. 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: Directory. L., 1991; Khromov S.P., Petrosyants M.A. Meteorology and climatology. 5th ed. M., 2001.
G. S. Golitsyn, N. A. Zaitseva.
The Earth's atmosphere is the gaseous envelope of our planet. By the way, almost all celestial bodies have similar shells, from the planets of the solar system to large asteroids. depends on many factors - the size of its speed, mass and many other parameters. But only the shell of our planet contains the components that allow us to live.
Earth's atmosphere: a brief history of its origin
It is believed that at the beginning of its existence our planet had no gas shell at all. But the young, newly formed celestial body was constantly evolving. The Earth's primary atmosphere was formed as a result of constant volcanic eruptions. This is how, over many thousands of years, a shell of water vapor, nitrogen, carbon and other elements (except oxygen) formed around the Earth.
Since the amount of moisture in the atmosphere is limited, its excess turned into precipitation - this is how seas, oceans and other bodies of water were formed. The first organisms that populated the planet appeared and developed in the aquatic environment. Most of them belonged to plant organisms that produce oxygen through photosynthesis. Thus, the Earth's atmosphere began to fill with this vital gas. And as a result of the accumulation of oxygen, the ozone layer was formed, which protected the planet from the harmful effects of ultraviolet radiation. It is these factors that created all the conditions for our existence.
The structure of the Earth's atmosphere
As you know, the gas shell of our planet consists of several layers - the troposphere, stratosphere, mesosphere, thermosphere. It is impossible to draw clear boundaries between these layers - it all depends on the time of year and the latitude of the planet.
The troposphere is the lower part of the gas shell, the height of which averages from 10 to 15 kilometers. This is where most of the moisture is concentrated. By the way, this is where all the moisture is located and clouds form. Due to the oxygen content, the troposphere supports the life activity of all organisms. In addition, it is crucial in shaping the weather and climatic features of the area - not only clouds, but also winds are formed here. Temperature drops with altitude.
Stratosphere - starts from the troposphere and ends at an altitude of 50 to 55 kilometers. Here the temperature increases with altitude. This part of the atmosphere contains virtually no water vapor, but does have an ozone layer. Sometimes here you can notice the formation of “pearl” clouds, which can only be seen at night - they are believed to be represented by highly condensed water drops.
The mesosphere stretches up to 80 kilometers up. In this layer you can notice a sharp drop in temperature as you move up. Turbulence is also highly developed here. By the way, so-called “noctilucent clouds” are formed in the mesosphere, which consist of small ice crystals - they can only be seen at night. It is interesting that there is practically no air at the upper boundary of the mesosphere - it is 200 times less than near the earth's surface.
The thermosphere is the upper layer of the earth's gas shell, in which it is customary to distinguish between the ionosphere and the exosphere. Interestingly, the temperature here rises very sharply with altitude - at an altitude of 800 kilometers from the earth's surface it is more than 1000 degrees Celsius. The ionosphere is characterized by highly diluted air and a huge content of active ions. As for the exosphere, this part of the atmosphere smoothly passes into interplanetary space. It is worth noting that the thermosphere does not contain air.
It can be noted that the Earth's atmosphere is a very important part of our planet, which remains a decisive factor in the emergence of life. It ensures life activity, maintains the existence of the hydrosphere (the watery shell of the planet) and protects from ultraviolet radiation.
10.045×10 3 J/(kg*K) (in the temperature range from 0-100°C), C v 8.3710*10 3 J/(kg*K) (0-1500°C). The solubility of air in water at 0°C is 0.036%, at 25°C - 0.22%.
Atmospheric composition
History of atmospheric formation
Early history
Currently, science cannot trace all stages of the formation of the Earth with one hundred percent accuracy. According to the most common theory, the Earth's atmosphere has had four different compositions over time. Initially, it consisted of light gases (hydrogen and helium) captured from interplanetary space. This is the so-called primary atmosphere. At the next stage, active volcanic activity led to the saturation of the atmosphere with gases other than hydrogen (hydrocarbons, ammonia, water vapor). This is how it was formed secondary atmosphere. This atmosphere was restorative. Further, the process of atmosphere formation was determined by the following factors:
- constant leakage of hydrogen 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).
The emergence of life and oxygen
With the appearance of living organisms on Earth as a result of photosynthesis, accompanied by the release of oxygen and the absorption of carbon dioxide, the composition of the atmosphere began to change. There is, however, data (analysis of the isotopic composition of atmospheric oxygen and that released during photosynthesis) that indicates the geological origin of atmospheric oxygen.
Initially, oxygen was spent on the oxidation of reduced compounds - hydrocarbons, ferrous form of iron contained in the oceans, etc. At the end of this stage, the oxygen content in the atmosphere began to increase.
In the 1990s, experiments were carried out to create a closed ecological system (“Biosphere 2”), during which it was not possible to create a stable system with a uniform air composition. The influence of microorganisms led to a decrease in oxygen levels and an increase in the amount of carbon dioxide.
Nitrogen
The formation of a large amount of N 2 is due to the oxidation of the primary ammonia-hydrogen atmosphere with molecular O 2, which began to come from the surface of the planet as a result of photosynthesis, supposedly about 3 billion years ago (according to another version, atmospheric oxygen is of geological origin). Nitrogen is oxidized to NO in the upper atmosphere, used in industry and bound by nitrogen-fixing bacteria, while N2 is released into the atmosphere as a result of denitrification of nitrates and other nitrogen-containing compounds.
Nitrogen N 2 is an inert gas and reacts only under specific conditions (for example, during a lightning discharge). Cyanobacteria and some bacteria (for example, nodule bacteria that form rhizobial symbiosis with leguminous plants) can oxidize it and convert it into biological form.
The oxidation of molecular nitrogen by electrical discharges is used in the industrial production of nitrogen fertilizers, and it also led to the formation of unique deposits of nitrate in the Chilean Atacama Desert.
Noble gases
Fuel combustion is the main source of polluting gases (CO, NO, SO2). Sulfur dioxide is oxidized by air O 2 to SO 3 in the upper layers of the atmosphere, which interacts with H 2 O and NH 3 vapors, and the resulting H 2 SO 4 and (NH 4) 2 SO 4 return to the Earth's surface along with precipitation. The use of internal combustion engines leads to significant atmospheric pollution with nitrogen oxides, hydrocarbons and Pb compounds.
Aerosol pollution of the atmosphere is caused by both natural causes (volcanic eruptions, dust storms, carryover of droplets of sea water and plant pollen particles, etc.) and human economic activities (mining ores and building materials, burning fuel, making cement, etc.) . Intense large-scale release of particulate matter into the atmosphere is one of the possible causes of climate change on the planet.
The structure of the atmosphere and characteristics of individual shells
The physical state of the atmosphere is determined by weather and climate. Basic parameters of the atmosphere: air density, pressure, temperature and composition. As altitude increases, air density and atmospheric pressure decrease. Temperature also changes with changes in altitude. The vertical structure of the atmosphere is characterized by different temperature and electrical properties, and different air conditions. Depending on the temperature in the atmosphere, the following main layers are distinguished: troposphere, stratosphere, mesosphere, thermosphere, exosphere (scattering sphere). The transitional regions of the atmosphere between neighboring shells are called tropopause, stratopause, etc., respectively.
Troposphere
Stratosphere
In the stratosphere, most of the short-wave part of ultraviolet radiation (180-200 nm) is retained and the energy of short waves is transformed. Under the influence of these rays, magnetic fields change, molecules disintegrate, ionization occurs, and new formation of gases and other chemical compounds occurs. These processes can be observed in the form of northern lights, lightning, and other glows.
In the stratosphere and higher layers, under the influence of solar radiation, gas molecules dissociate into atoms (above 80 km CO 2 and H 2 dissociate, above 150 km - O 2, above 300 km - H 2). At an altitude of 100-400 km, ionization of gases also occurs in the ionosphere; at an altitude of 320 km, the concentration of charged particles (O + 2, O − 2, N + 2) is ~ 1/300 of the concentration of neutral particles. In the upper layers of the atmosphere there are free radicals - OH, HO 2, etc.
There is almost no water vapor in the stratosphere.
Mesosphere
Up to an altitude of 100 km, the atmosphere is a homogeneous, well-mixed mixture of gases. In higher layers, the distribution of gases by height depends on their molecular weights; the concentration of heavier gases decreases faster with distance from the Earth's surface. Due to a 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 in time and space are observed.
At an altitude of about 2000-3000 km, the exosphere gradually turns into the so-called near-space vacuum, which is filled with highly rarefied particles of interplanetary gas, mainly hydrogen atoms. But this gas represents only part of the interplanetary matter. The other part consists of dust particles of cometary and meteoric origin. In addition to these extremely rarefied 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 - 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 neutronosphere 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 the area where gravity affects the separation of gases, since their mixing at such an altitude is negligible. This implies a 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 the turbopause, it lies at an altitude of about 120 km.
Atmospheric properties
Already at an altitude of 5 km above sea level, an untrained person begins to experience oxygen starvation and without adaptation, a person’s performance is significantly reduced. The physiological zone of the atmosphere ends here. Human breathing becomes impossible at an altitude of 15 km, although up to approximately 115 km the atmosphere contains oxygen.
The atmosphere supplies us with the oxygen necessary for breathing. However, due to the drop in the total pressure of the atmosphere, as you rise to altitude, the partial pressure of oxygen decreases accordingly.
The human lungs constantly contain about 3 liters of alveolar air. The partial pressure of oxygen in alveolar air at normal atmospheric pressure is 110 mmHg. Art., carbon dioxide pressure - 40 mm Hg. Art., and water vapor −47 mm Hg. Art. With increasing altitude, oxygen pressure drops, and the total vapor pressure of water and carbon dioxide in the lungs remains almost constant - about 87 mm Hg. Art. The supply of oxygen to the lungs will completely stop when the ambient air pressure 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 altitude, 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.
Dense layers of air - the troposphere and stratosphere - protect us from the damaging effects of 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 is dangerous for humans.
The structure of the Earth's atmosphere
The atmosphere is the gaseous shell of the Earth with the aerosol particles it contains, moving together with the Earth in space as a single whole and at the same time taking part in the rotation of the Earth. Most of our life takes place at the bottom of the atmosphere.
Almost all the planets of our solar system have their own atmospheres, but only the earth’s atmosphere is capable of supporting life.
When our planet formed 4.5 billion years ago, it was apparently devoid of an atmosphere. The atmosphere was formed as a result of volcanic emissions of water vapor mixed with carbon dioxide, nitrogen and other chemicals from the interior of the young planet. But the atmosphere can contain a limited amount of moisture, so its excess as a result of condensation gave rise to the oceans. But then the atmosphere was devoid of oxygen. The first living organisms that originated and developed in the ocean, as a result of the photosynthesis reaction (H 2 O + CO 2 = CH 2 O + O 2), began to release small portions of oxygen, which began to enter the atmosphere.
The formation of oxygen in the Earth's atmosphere led to the formation of the ozone layer at altitudes of approximately 8 – 30 km. And, thus, our planet has acquired protection from the harmful effects of ultraviolet study. This circumstance served as an impetus for the further evolution of life forms on Earth, because As a result of increased photosynthesis, the amount of oxygen in the atmosphere began to grow rapidly, which contributed to the formation and maintenance of life forms, including on land.
Today our atmosphere consists of 78.1% nitrogen, 21% oxygen, 0.9% argon, and 0.04% carbon dioxide. Very small fractions compared to the main gases are neon, helium, methane, and krypton.
The gas particles contained in the atmosphere are affected by the force of gravity of the Earth. And, given that air is compressible, its density gradually decreases with height, passing into outer space without a clear boundary. Half of the total mass of the earth's atmosphere is concentrated in the lower 5 km, three quarters in the lower 10 km, nine tenths in the lower 20 km. 99% of the mass of the Earth's atmosphere is concentrated below an altitude of 30 km, which is only 0.5% of the equatorial radius of our planet.
At sea level, the number of atoms and molecules per cubic centimeter of air is about 2 * 10 19, at an altitude of 600 km only 2 * 10 7. At sea level, an atom or molecule travels approximately 7 * 10 -6 cm before colliding with another particle. At an altitude of 600 km this distance is about 10 km. And at sea level, about 7 * 10 9 such collisions occur every second, at an altitude of 600 km - only about one per minute!
But not only pressure changes with altitude. The temperature also changes. For example, at the foot of a high mountain it can be quite hot, while the top of the mountain is covered with snow and the temperature there is at the same time below zero. And if you take a plane to an altitude of about 10-11 km, you can hear a message that it is -50 degrees outside, while at the surface of the earth it is 60-70 degrees warmer...
Initially, scientists assumed that the temperature decreases with height until it reaches absolute zero (-273.16°C). But that's not true.
The Earth's atmosphere consists of four layers: troposphere, stratosphere, mesosphere, ionosphere (thermosphere). This division into layers was also adopted based on data on temperature changes with height. The lowest layer, where air temperature decreases with height, is called the troposphere. The layer above the troposphere, where the temperature drop stops, is replaced by isotherm, and finally the temperature begins to rise, is called the stratosphere. The layer above the stratosphere in which the temperature rapidly drops again is the mesosphere. And finally, the layer where the temperature begins to rise again is called the ionosphere or thermosphere.
The troposphere extends on average to the lower 12 km. This is where our weather is formed. The highest clouds (cirrus) form in the uppermost layers of the troposphere. The temperature in the troposphere decreases adiabatically with height, i.e. The temperature change occurs due to the decrease in pressure with height. The temperature profile of the troposphere is largely determined by solar radiation reaching the Earth's surface. As a result of the heating of the Earth's surface by the Sun, convective and turbulent flows are formed, directed upward, which form the weather. It is worth noting that the influence of the underlying surface on the lower layers of the troposphere extends to a height of approximately 1.5 km. Of course, excluding mountainous areas.
The upper boundary of the troposphere is the tropopause - an isothermal layer. Consider the characteristic appearance of thunderclouds, the top of which is a “burst” of cirrus clouds called an “anvil.” This “anvil” just “spreads” under the tropopause, because due to isotherm, the ascending air currents are significantly weakened, and the cloud stops developing vertically. But in special, rare cases, the tops of cumulonimbus clouds can invade the lower layers of the stratosphere, breaking the tropopause.
The height of the tropopause depends on latitude. Thus, at the equator it is located at an altitude of approximately 16 km, and its temperature is about –80°C. At the poles, the tropopause is located lower, at approximately 8 km altitude. In summer the temperature here is –40°C, and –60°C in winter. Thus, despite higher temperatures at the Earth's surface, the tropical tropopause is much colder than at the poles.
