Atmosphere

Atmosphere

ATMOSPHERE OF THE EARTH (from the Greek words "atmos" (vapour) and "sphaira" (ball) * EN: atmosphere; DE: Atmosphare; FR: atmosphere; ES: atmosfera; RU: атмосфера) is the gaseous envelope, which is surrounding the Earth, and is participating in its daily rotation. The mass of the atmosphere is approximately 5.15 • 10^15 tonnes. The atmosphere ensures the possibility of the life on the Earth, and provides the influence onto the geological processes.

Origin and role of the atmosphere. Modern atmosphere has, apparently, the secondary origin; it has originated from the gases, which have been emitted by the solid shell of the Earth (lithosphere) after the formation of the planet. During the geological history of the Earth, the atmosphere has experienced the significant evolution under the influence of the series of the factors: the dissipation (scattering) of the gaseous molecules into the outer space, the emission of the gases from the lithosphere as the result of the volcanic activity, the dissociation (splitting) of the molecules under the influence of the solar ultraviolet radiation, the chemical reactions among the components of the atmosphere and the rocks, which form the Earth's crust, the accretion (capture) of the meteoric substance. The evolution of the atmosphere is tightly associated not only with the geological and geochemical processes, but also with the activity of the living organisms, particularly of the human persons (anthropogenic factor). The study of the changes of the composition of the atmosphere during the past times has shown, that already during the early periods of the Phanerozoic, the quantity of oxygen within the air constituted approximately 1/3 of its modern value. The content of oxygen within the atmosphere has sharply increased during the Devonian and Carboniferous, when it possibly exceeded the modern level. After the decrease during the Permian and Triassic periods, it has again increased, reaching the maximal value during the Jurassic, after which there has occured the new decrease, which continues during our time. The quantity of the carbon dioxide also changed significantly during the Phanerozoic. From the Cambrian to the Paleogene, the concentration of the CO2 ranged within the limits of 0.1-0.4%. Its decrease to the modern level (0.03%) has occurred during the Oligocene and (after the certain increase during the Miocene) during the Pliocene. The atmospheric gases provide the substantial influence onto the evolution of the lithosphere. For example, the largest portion of the carbon dioxide, which has originally arrived into the atmosphere from the lithosphere, has been then accumulated within the carbonatic rocks. The atmospheric oxygen and water vapour are the most important factors, which are acting onto the rocks. During the entire history of the Earth, the atmospheric precipitation play the great role during the supergene process. There has at least equally important significance the activity of the wind (see the "Weathering" article), which is transporting the tiny fractions of the destructed rocks along the great distances. There significantly influence the destruction of the rocks the fluctuations of the temperature, and other atmospheric factors.

The atmosphere protects the surface of the Earth against the destructive actions of the falling stones (meteorites), the greatest quantity of which burns during the entrance into its dense layers. Flora and fauna, which have provided the substantial influence onto the evolution of the atmosphere, themselves depend very much on the atmospheric conditions. The layer of ozone within the atmosphere stops the greatest amount of the ultraviolet radiation of the sun, which could act deadly onto the live organisms. The oxygen of the atmosphere is used during the process of the breathing by the animals and plants, the carbon dioxide is used during the process of the nutrition of the plants.

The atmospheric air is the important source of the chemical raw materials for the industry: for example, the atmospheric nitrogen is the raw material for the obtainment of ammonia, nitric acid, and other chemical compounds; they use the oxygen within the various branches of the national economy. There obtains the ever increasing importance the mastering of the energy of the wind, especially within the regions, where are absent other sources of energy.

Structure of the atmosphere. There is characteristical for the atmosphere the clearly expressed stratification (Figure), which is determined by the peculiarities of the vertical distribution of temperature and density of the gases, which are composing it. The distribution of the temperature is very complicated, the density decreases according to the exponential law (80% of the total mass of the atmosphere is concentrated within the troposphere).

The transitional region between the atmosphere and interplanetary space is the outermost part of it, namely, the exosphere, which is consisting of the rarefied hydrogen. At the heights of 1-20 thousand kilometres, the gravitational field of the Earth is no longer able to retain gas, and the molecules of hydrogen disperse themselves within the outer space. The region of the dissipation of hydrogen creates the phenomenon of geocorona. The very first flights of the artificial satellites have discovered, that the Earth is surrounded by several envelopes of the charged particles, the gas-kinetic temperature of which reaches several thousand degrees. These envelopes have got the name of the radiation belts. Charged particles, namely, the electrons and protons of the solar origin, are captured by the magnetic field of the Earth, and cause various phenomena within the atmosphere, for example, the polar auroras. The radiation belts constitute the part of the magnetosphere.

All atmospheric parameters, namely, the temperature, pressure, density, are characterized by the significant spatial-temporal variability (latitudinal, annual, seasonal, daily). There has been also uncovered their dependence on the flares of the sun.

(Table) The composition of the atmosphere
Components Concentration, % (by volume)
Nitrogen 78.084
Oxygen 20.9476
Argon 0.934
Carbon dioxide 0.0314
Neon 0.001818
Helium 0.000524
Methane 0.0002
Krypton 0.000114
Hydrogen 0.00005
Nitrous oxide 0.00005
Xenon 0.0000087
Sulfur dioxide from 0 to 0.0001
Ozone from 0 to 0.000007 during summer
from 0 to 0.000002 during winter
Nitrogen dioxide from 0 to 0.000002
Ammonia traces
Carbon monoxide traces
Iodine traces

Composition of the atmosphere. The main components of the atmosphere are nitrogen, oxygen, and also argon, carbon dioxide, neon, and other gases (Table).

The most important variable constituent part of the atmosphere is the water vapour. The change of its concentration ranges within the wide limits: from 3% near the Earth's surface on the equator to 0.2% within the polar latitudes. The major amount of its mass is concentrated within the troposphere, the content is determined by the ratio of the processes of evaporation, condensation, and horizontal transfer. As the result of the condensation of the water vapour, there form themselves the clouds, and fall out the atmospheric precipitations (rain, hail, snow, dew, fog). The substantial variable component of the atmosphere is the carbon dioxide, the change of the content of which is associated with the life activity of the plants (with the processes of the photosynthesis) and with the solubility within the sea water (with the gas exchange between the ocean and atmosphere). There is observed the increase of the content of the carbon dioxide, which is caused by the industrial pollution, which provides the influence onto the climate.

Radiative, thermal, and water balances of the atmosphere. There is practically the single source of the energy for all the physical processes, which develop themselves within the atmosphere, namely, the solar radiation, which is passed through by the "windows of transparency" of the atmosphere. The main peculiarity of the radiative regime of atmosphere, namely, the so-called greenhouse effect, is that there is almost not absorbed by it the radiation within the optical range (the greater portion of the radiation reaches the Earth's surface and heats it), and there is not passed through along the reverse direction the infrared (thermal) radiation of the Earth, which significantly decreases the heat output of the planet and increases its temperature. The part of the solar radiation, which reaches the atmosphere, is absorbed (mainly by the water vapour, carbon dioxide, ozone, and aerosols), the other part is scattered by the gaseous molecules (which explains the blue colour of the sky), dust particles, and fluctuations of the density. The scattered radiation combines with the direct sunlight and, after reaching the Earth's surface, is partially reflected from it, and is partially absorbed. The share of the reflected radiation depends on the reflective ability of the underlying surface (albedo). The radiation, which has been absorbed by the Earth's surface, is converted into the infrared radiation, which is directed into the atmosphere. In its turn, the atmosphere is also the source of the long-wave radiation, which is directed toward the Earth's surface (the so-called counterradiation of the atmosphere), and into the outer space (the so-called outgoing radiation). The difference between the short-wave radiation, which has been absorbed by the Earth's surface, and the effective radiation of the atmosphere, is named the radiative balance.

The conversion of the energy of the radiation of the sun after its absorption by the Earth's surface and atmosphere constitutes the thermal balance of the Earth. The losses of the heat from the atmosphere into the outer space far exceed the energy, which is brought by the absorbed radiation, but the deficit is replenished by the influx of the heat on the account of the mechanical heat exchange (turbulence) and by the heat of the condensation of the water vapour. The magnitude of the latter within the atmosphere is numerically equal to the losses of the heat for the evaporation from the surface of the Earth (see the "Water balance" article).

Movement of the air. As the consequence of the great mobility of the atmospheric air, at all the altitudes within the atmosphere, there are observed the winds. The directions of the movement of the air depend on many factors, but the main of them is the uneveness of the heating of the atmosphere within the different regions. As the consequence of this, it is possible to liken the atmosphere to the giant heat engine, which converts the radiant energy, which is coming from the sun, into the kinetic energy of the moving air masses. According to the approximate estimates, the efficiency of this process is 2%, which corresponds to the power of 2.26 • 10^15 watts. This energy is spent onto the forming of the large-scale vortices (cyclones and anticyclones), and onto the maintaining of the stable global system of winds (monsoons and trade winds). Along with the air currents of the large scales, there are observed within the lower layers of the atmosphere the numerous local circulations of the air (breeze, bora, mountain-valley winds, and others). There are usually noted within all air currents the pulsations, which are corresponding to the movement of the air vortices of the medium and small sizes. The noticeable changes of the meteorological conditions are achieved with such meliorative measures, as irrigation, growing of the forests for the field protection, draining of the swampy regions, creation of the artificial seas. These changes are mainly limited by the near-surface layer of the air.

Besides the directed impacts onto the weather and climate, human activity provides the influence onto the composition of the atmosphere. The pollution of the atmosphere on the account of the activity of the enterprises of the energetical, metallurgical, chemical, and mining industries, proceeds as the result of the ejection into the air of mainly the exhaust gases (90%), and also of the dust and aerosols. The total mass of the aerosols, which are ejected annually into the air as the result of the human activity, is approximately 300 million tonnes. In association with this, they conduct within many countries the works for the monitoring of the pollution of the air. The rapid growth of the energetical economy leads to the additional warming of the atmosphere, which is yet noticeable only within the large industrial centres, but in the future may lead to the changes of the climate on the large territories. The pollution of the atmosphere by the mining enterprises depends on the geological nature of the deposit, which is being developed, on the technology of the extraction and processing of the useful minerals. For example, the emission of methane from the layers of coal during its development amounts to approximately 90 million cubic metres per year.

During the conducting of the blasting works (for the breaking of the rocks), there are emitted during the year into the atmosphere approximately 8 million cubic metres of gases, the largest portion of which are inert, which are not providing the harmful impact onto the environment. The intensity of the emission of the gases as the result of the oxidative processes within the dumps of the waste rocks is relatively large. The abundant dust release proceeds during the processing of the ores, and also at the mining enterprises, which are developing the deposits by the open pit method with the usage of the blasting works, particularly within the arid regions, and within the regions, which are subjects to the actions of the winds. The mineral particles pollute the air space for a short time, mainly near the enterprises, settling onto the soil, onto the surface of the water bodies and other objects.

For the prevention of the pollution of the atmosphere with gases, they use: the capturing of methane, foam-air and air-water curtains, cleaning of the exhaust gases, and electrical prime mover (instead of the diesel one) for the mining and transportation equipment, the insulation of the goaf spaces (siltation, stowing), injection of the water or anti-pyrogenous solutions into the layers of coal, and so on. They introduce into the processes of the processing of the ore the new technologies (including the ones with the closed-loop productive cycles), gas cleaning installations, diversion of the smoke and gas into the high layers of the atmosphere, and so on. The decreasing of the ejection of the dust and aerosols into the atmosphere during the development of deposits is achieved by the method of the suppression, binding, and capturing of the dust during the process of the drilling-blasting and loading-transportation works (irrigation by the water, solutions, foams, coating onto the dumps, sides, and roads of the emulsion or film coatings, and so on). During the transportation of the ore, they use the pipelines, containers, film and emulsion coatings, and during the processing, they use the cleaning by the filters, covering of the tailings with pebbles, organic resins, recultivation, and recycling of the tailings.