The atmosphere is the outermost gas sphere of the earth, surrounding the sea and land. The thickness of the atmosphere is about 1000 kilometers, but there is no obvious boundary.[1]This layer of gas is mainly composed of nitrogen, oxygen and a small amount of other gases (such as carbon dioxide, argon, water vapor, etc.), which plays a vital role in the survival of life on the earth and the formation of the earth's climate.According to different division rules, the atmosphere can be further divided into several sub layers. Taking the temperature structure as an example, the atmosphere can be divided into the troposphere, stratosphere, mesosphere, thermosphere and exosphere. Each sub layer has its specific temperature and pressure distribution characteristics, as well as specific climate and weather phenomena.[2]
The atmosphere, also known as the atmosphere, is a layer of mixed gas surrounding the earth due to gravity. It is the outermost gas sphere around the earthoceanOn land, there is no exact upper boundary of the atmosphere. There are still thin gases and basic particles 2000~16000 kilometers above the surface. There are also small quantities of gases underground, in soil and some rocks. They can also be considered as a part of the atmosphere. The main components of the earth's atmosphere are nitrogen, oxygen, argon, carbon dioxide and trace gases with a proportion of less than 0.04%,These mixtures are called air.
component
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The composition of the atmosphere mainly includesnitrogen, accounting for 78.1%;Oxygen accounted for 20.9%;Argon accounts for 0.93%;There are a fewcarbon dioxide、Noble gas(helium, neon, argon, krypton, xenon, radon) and water vapor.The air density of the atmosphere decreases with height, and the higher the height, the thinner the air.The thickness of the atmosphere is about 1000 kilometers, but there is no obvious boundary.
Gas
Volume fraction?
Gas
volume fraction
(×10)
?(×10)
nitrogen
780 900
krypton
one
oxygen
209 400
nitric oxide
one point five
argon
9 300
hydrogen
one point five
carbon dioxide
three hundred and fifteen
xenon
one point zero eight
neon
eighteen
Nitrogen dioxide
one point zero two
methane
1.0～1.2
The components in the atmosphere are unstable. Whether it is natural disasters or man-made influences, new substances will appear in the atmosphere, or the content of a certain component excessively exceeds the average value under the natural state, or the content of a certain component decreases, which will affect the normal development and growth of organisms and cause harm to human beings. This is the main object that environmental protection workers should study[1]。
Layered characteristics
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The composition and distribution of the earth's atmosphere are very complex, so the vertical structure of the atmosphere is also very complex. Nowadays, the atmosphere is generally stratified according to the vertical distribution characteristics of atmospheric temperature, composition and ionization.
According to the temperature structure of the atmosphere
The atmosphere can be divided into troposphere, stratosphere, mesosphere, thermosphere and exosphere according to the vertical temperature structure of the atmosphere, that is, the thermal structure of the neutral composition of the atmosphere.[2]
troposphere
1. Definition
troposphereLocated in the lowest layer of the atmosphere, it extends from the earth's surface to the upper air until the tropopause, the starting point of the stratosphere.The average thickness is about 12km, and its thickness varies from 8km above the poles of the earth to 17km above the equator. It is the densest layer in the atmosphere, concentrating about 75% of the atmospheric mass and more than 90% of the water vapor mass.Its lower boundary is connected with the ground, and the upper boundary height varies with geographical latitude and seasons.Its altitude varies according to latitude. Its average altitude is 17~18 km in low latitude areas, 10~12 km in middle latitude areas, and 8~9 km in high latitude areas. It is higher in summer than in winter.
2. Features
(1) The temperature decreases with the increase of height: this is because this layer cannot directly absorb the short wave radiation of the sun, but can absorb the long wave radiation reflected from the ground to heat the atmosphere from the underlying surface.Therefore, the air near the ground is heated more than the air far from the ground.The temperature will drop by 6.5 degrees for every 1km increase.
(2) Air convection: because the surface of the lithosphere and hydrosphere is heated by the sun, and the heat radiation heats the lower air, the cold and hot air will have vertical convection, and because the ground is divided into sea and land, day and night, and the latitude difference, the temperature in different regions is also different, which forms the horizontal movement of the air.
(3) The horizontal distribution of temperature, humidity and other elements is uneven: the atmosphere is in contact with the surface, and water vapor, dust, microorganisms and toxic substances generated by human activities enter the air layer, so in this layer, besides the vertical and horizontal movement of air flow, the chemical process is very active, and with the air mass cooling or heating, water vapor forms rain, snow, hail, frost, dew, cloudFog and other weather phenomena.
stratosphere
1. Definition
The atmosphere about 10~50 kilometers from the surface.It is located above the troposphere and below the exosphere.The stratosphere, also known as the stratosphere, is a layer of the earth's atmosphere that is hot above and cold below. This layer is divided into different temperature layers, with the middle high temperature layer at the top and the low temperature layer at the bottom.
2. Features
It is just the opposite of the troposphere, which is located below it and close to the earth's surface. The troposphere is cold at the top and hot at the bottom.In the mid latitude region, the stratosphere is located at an altitude of 10~50km from the surface, while in the polar region, it starts at about 8km from the surface.Above the troposphere, up to the layer 50 kilometers above the sea level, the airflow is mainly in the horizontal direction, and the convection phenomenon is weakened. This atmosphere is called the "stratosphere", also known as the "stratosphere".There is basically no water vapor here. It is sunny and cloudless, with little weather change, and it is suitable for aircraft navigation.At a height of 20~30km, the ozone layer is formed by oxygen molecules under the action of ultraviolet light, which acts as a barrier to protect the life on the earth from the sun's ultraviolet rays andHigh-energy particleAttacks.
Middle layer
1. Definition
The middle layer is also called the middle layer.The atmosphere from the top of the stratosphere to 85 kilometers.
2. Features
Because the ozone content in this layer is low, and the solar short wave radiation that can be directly absorbed by nitrogen, oxygen, etc. has been mostly absorbed by the upper atmosphere, the vertical decline rate of temperature is large, and the convection movement is strong.The temperature near the top of the mesosphere is about 190K;Air molecules can ionize after absorbing solar ultraviolet radiation, which is customarily called the D layer of the ionosphere;Sometimes noctilucent clouds appear at dusk in summer in high latitudes.
Thermosphere
1. Definition
The atmosphere above the mesopause is about 800 km high.
2. Features
Due to the photochemical decomposition and ionization reaction of strong ultraviolet radiation (<0.18um) in the solar radiation, the temperature of this layer increases rapidly with the increase of height.In this layer, the thin air molecules or atoms are excited by the high-speed charged particle flow from the sun, and emit visible light when they collide with other particles or return to the ground state through their own radiation, which is called aurora.
Exosphere
1. Definition
The outer atmosphere above the thermosphere extends to 1000 kilometers from the earth's surface.The temperature here is very high, up to thousands of degrees;The atmosphere is extremely thin, and its density is one billionth of that at sea level.
2. Features
The outer atmosphere is also called the magnetosphere. It is the outermost layer of the atmosphere and the transition area from the atmosphere to interstellar space. There is no obvious boundary outside.In general, the upper limit is lower near the geomagnetic pole, and the near magnetic equator is on the side toward the sun, about 9~10 earth radii are high, in other words, about 65000 kilometers high.The air is extremely thin here.Usually, the height of the atmosphere is within 1000 kilometers, that is, within the ionosphere, that is, 1000 kilometers thick.
According to the composition and structure of the atmosphere
Homogeneous layer
From the ground to the height of 86~90km, including the troposphere, stratosphere and mesosphere, the atmosphere is evenly mixed due to turbulent diffusion. The proportion of various components in the atmosphere, except ozone, remains unchanged in the vertical and horizontal directions. The average molar mass of dry air M=28.964kg/(kmol).This layer of atmosphere is called the homosphere, also called the turbulent layer.
Heterogeneous layer
The atmosphere above the homogeneous layer is called the heterosphere.In the heterogeneous layer, due to gravity separation and photochemical action, the proportion of atmospheric components changes with height, and the average molar mass decreases with height.At the altitude of 500 km, the five main neutral components of the atmosphere are O, He, N and H, O2;At the height of 1000km, there are only He, H and O.At different heights of the heterogeneous layer, from bottom to top, the gas components with the largest number density are oxygen atoms (180~650 km), helium atoms (650~1000 km) and hydrogen atoms (more than 1000 km).The peak value of oxygen atom concentration is about 100km high, and its relative concentration increases rapidly with the height. This is because the solar ultraviolet radiation at high altitude is strong, more atomic oxygen is generated by photolysis, while the gas molecular density is small, collision frequency is small, and recombination opportunities are few, so that atomic oxygen can become a stable component.The distribution of air components with height is also related to solar activity.
According to the pressure structure of atmosphere
Barometric layer
More than 500km above the ground, there are few molecules, and the probability of collision is very small. It is difficult for molecules to reach thermal equilibrium due to their respective movements.Therefore, only below 500km, the atmospheric pressure obeys the pressure height relationship, which is called the barometric layer.
Outer atmosphere
In the atmosphere above 500km and up to 2000-3000km, most molecules are ionized under the action of solar ultraviolet and cosmic rays, making the content of protons far exceed that of neutral oxygen atoms. Some fast molecules and ions can overcome the earth's force field and escape to the interplanetary space, so they are called the outer atmosphere or escape layer.
According to the ionization structure of the atmosphere
According to the electromagnetic characteristics of the atmosphere at different altitudes, it can be divided into the neutral layer (below 60km), the ionosphere and the magnetosphere.
In the atmosphere between 60km and 500-1000km above the earth's surface, the ionosphere 0 starts to ionize into positive ions and free electrons under the action of solar electromagnetic radiation (mainly ultraviolet and X-ray shorter than 0.1pm) and particle radiation (protons, electrons, etc., and cosmic ray particles emitted from the sun).Once these positive ions and free electrons are generated, they tend to recombine, and finally establish a balance, forming a vertical distribution of electron density.Although the electron density only accounts for a few percent of the neutral gas, because it is ionized, it causes some very important phenomena in the upper atmosphere, including the generation of current and magnetic field, the reflection of radio waves and various plasma processes.
The magnetosphere starts at 500 and 1000 km, and its outer boundary is called the magnetopause.Since the electron density above the ionosphere decreases with height, there is little chance of collision between charged particles and neutral gas particles at this height, and the interaction is very small, so charged particles are increasingly controlled by the earth's magnetic field, and make cyclotron motion along the earth's magnetic line of force.
effect
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The role of the atmosphere on the earth is mainly reflected in the following aspects:
1. Maintenance water volume: the atmosphere can maintain the circulation of the hydrosphere.All biological species on the earth must rely on water to live a healthy life. The atmosphere is saturated with the gaseous water evaporated by the earth's sunlight every day, and can return to the earth in the form of rain or snow and morning fog, which can ensure the cycle of the earth's hydrosphere, complete the timely replenishment of the biosphere, and contribute to the healthy life of the biosphere.Ensure the fluctuation of liquid water (land).Under the effect of atmospheric enclosure, it can adhere to the fluctuation of liquid water on the earth's surface, ensure the storage of liquid water on land, rivers, lakes and other places, and is conducive to the benign life of the earth's biosphere.[5]
2. Protective barrier: acts as a shield for solar thermal radiation.The ultraviolet heat radiation of sunlight is very strong, and the atmosphere can act as a shield for it, which can reduce the ultraviolet radiation of sunlight to the life compliance range of the Earth's biosphere, which is conducive to the benign growth of the Earth's biosphere.[4]The composition of the atmosphere is just suitable for human needs, so that the ultraviolet radiation can hardly reach the ground. This kind of solar ultraviolet radiation is very harmful to biology.At the same time, the atmosphere prevents the ground from being attacked by rocks from the sky.Due to the existence of atmosphere around the earth, the stones intruded by the outside world are subjected to intense friction, getting hotter and hotter, and finally cause spontaneous combustion.At night, we can often see the shooting stars in the sky, which are burning stones.But most of the stones burned out before they fell to the ground, turning into gas and dust.[5]To sum up, the atmosphere can not only prevent rocks from space from attacking the ground, but also reduce the arrival of harmful ultraviolet and X-ray rays to organisms and human beings.
3. Temperature regulation: there is a layer of atmosphere about 100 kilometers thick around the earth.This layer of atmosphere is the basic condition for the survival of life on the earth. It provides indispensable oxygen for life and human beings at all times, and can keep the ground at an appropriate temperature.As the solar radiation passes through the atmosphere around the earth, the atmosphere will absorb, scatter and reflect part of it, which will weaken the total energy of the sun hitting the earth.Therefore, the intensity of direct solar radiation reaching the earth's surface changes with the physical state of the atmosphere and the length of the path of solar rays through the atmosphere.By absorbing, scattering and reflecting solar radiation, the atmosphere keeps the surface at an appropriate temperature.[5]
4. Oxygen maintenance: The atmosphere provides oxygen for living creatures and human beings, and can maintain the oxygen concentration on the surface.Under the effect of atmospheric enclosure, the oxygen distributed by the land and the biosphere every day cannot escape from outer space, maintaining the oxygen on the surface of the earth and helping the biosphere to supply oxygen for life.[5]
5. Block ultraviolet radiation: ozone in the atmosphere can absorb ultraviolet radiation to a large extent, and the existence of the ozone layer is crucial to block harmful solar ultraviolet radiation.[3]
