The ozone layer is the high level of ozone concentration in the stratosphere of the atmosphere.The part with the highest concentration is at the height of 20-25 km.If the ozone in the ozone layer is corrected to the standard condition, its average thickness is only about 3mm.Ozone content varies with latitude, season and weather.Ultraviolet radiation is absorbed by ozone at high altitude, which has a warming effect on the atmosphere. At the same time, it protects the living things on the earth from the damage of far ultraviolet radiation. A small amount of ultraviolet radiation that passes through has a bactericidal effect, which is of great benefit to living things.
In December 2022, China has achieved remarkable results in implementing the Montreal Protocol on Substances that Deplete the Ozone Layer for 30 years. It has eliminated about 504000 tons of ozone depleting substances (ODS) accumulatively, which has brought huge benefits to climate change mitigation while protecting the ozone layerBenefits.[7]
On September 14, 2023, at the "2023 China International Day for the Protection of the Ozone Layer Commemoration Conference", it was introduced that since China joined the Montreal Protocol on Substances that Deplete the Ozone Layer in 1991, by 2022, the production and use of ozone depleting substances (ODS) had been eliminated in an accumulative amount of 628000 tons, accounting for more than half of the amount eliminated by developing countries.In the 30 years from 1991 to 2020, China avoided about 26 billion tons of carbon dioxide equivalent greenhouse gas emissions in the process of eliminating ODS.[8]
Chinese name
ozone layer
Foreign name
ozone layer
Nature
The part of stratosphere with relatively high ozone concentration
Impact and function
Effectively prevent ultraviolet rays from getting into the ground
Human True UnderstandingozoneMore than 150 years ago, GermanyXianbeinDr. (Schanbein) first proposed thatWater electrolysisAnd the odor generated in spark discharge is the same as that generated after lightning in nature. Dr. Xianbein thought that the odor was unpleasant, so he named it ozone.The ozone layer was discovered by French scientist Fabry in the early 20th century.1930 UKgeophysicsKaapman proposed that ozone in the atmosphere is mainly produced when oxygen atoms collide with oxygen molecules in a three body collision with the participation of a third neutral molecule.Above 60 kilometers, the sun's ultraviolet rays are strong, oxygen molecules are largely dissociated, the chance of three body collision is reduced, and the ozone content is very little.At low altitude below 5km, the ultraviolet ray is greatly weakened, and there are few oxygen atoms, so it is difficult to form ozone.There are enough oxygen atoms and enough oxygen molecules in the altitude range of 20-25km, which is most conducive to the three body collision, and the ozone formed is about 50 billion tons every year.[1]
Ozone profile in the atmosphere
formation
The ozone in nature is mostly distributed in the atmosphere 20km~50km away from the ground, which is called the ozone layer.The ozone in the ozone layer is mainly produced by ultraviolet light.The ultraviolet ray in the sun light is divided into long wave and short wave. When oxygen molecules in the atmosphere (containing 21%) are exposed to short wave ultraviolet rays,Oxygen moleculeWill decompose into atomic states.Oxygen atomIt is extremely unstable and easy to react with other substances.Such as hydrogen (Htwo）Water generated by reaction (HtwoO) , generated by reaction with carbon (C)carbon dioxide（COtwo）。Similarly, with oxygen molecule (Otwo）During the reaction, ozone (Othree）。After the formation of ozone, because its specific gravity is greater than that of oxygen, it will gradually fall to the bottom of the ozone layer. During the fall, it will change (rise) with the temperature,ozoneThe more obvious the instability is, the morelong waveUltraviolet radiation reduces to oxygen again.The ozone layer maintains the conversion between oxygen and ozonedynamic equilibrium。[2]
Encyclopedia x ignorance: illustrating the ozone layer
Spatiotemporal change
The total amount of ozone in the Earth's atmosphere has obvious temporal and spatial changes: it is the lowest near the equator, and the highest near the latitude of 60 °;It is the largest in spring and the smallest in autumn in any region;In a day, the ozone content is usually higher at night than during the day;In the mid latitude region of Asia, when the Siberian air mass intrudes, the total amount of ozone increases significantly, while when the equatorial air mass comes, its total amount decreases.[3]
About 1% of the sun's ultraviolet rays reach the ground.Especially inair pollutionLighter forests, mountains, and coastal areas have more ultraviolet rays and are rich in ozone.
Ozonosphere action
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Ozone layer blocks ultraviolet rays
The atmospheric ozone layer has three main functions.One is protection. The ozone layer can absorb ultraviolet rays with wavelength below 306.3nm in sunlight, mainly part of UV-B (wavelength 290-300nm) and all of UV-C (wavelength<290nm), to protect human beings, animals and plants on the earth from the damage of short wave ultraviolet rays.Only UV-A and a small amount ofMedium waveUltraviolet UV-B can radiate to the ground, and the damage of UV-B to biological cells is much less than that of UV-B.So the ozone layer is like a protective umbrella to protect the life on the earth to survive and multiply.
The second is heating. Ozone absorbs the ultraviolet ray in the sunlight and converts it into heat energy to heat the atmosphere. Because of this effect, there is a peak in the atmospheric temperature structure at an altitude of about 50km, and there is a warming layer 15~50km above the earth.It is because of the existence of ozone that the stratosphere exists.But the planets outside the earth do not existozoneAnd oxygen, so there is no stratosphere.The temperature structure of the atmosphere has an important impact on the atmospheric cycle, which is also caused by the high distribution of ozone.
The third isgreenhouse gasesThe role oftroposphereThe role of ozone is also very important in the upper and lower stratosphere, that is, at a very low temperature.If the ozone at this height decreases, it will generate the power to reduce the ground temperature.Therefore, the height distribution and change of ozone are extremely important.
Ozone in the stratosphere absorbs a large amount of ultraviolet radiation (240-329nm, called UV-B wavelength) harmful to humans, animals and plants emitted by the sun, providing the earth with a barrier to prevent the harmful effects of ultraviolet radiation.On the other hand, ozone spreads throughout the troposphere, but it plays an adverse role as a greenhouse gas.Ozone depletion in the stratosphere is mainly through dynamic migration to the troposphere, where most of the matrix and carrier molecules with active catalytic effect are obtained, and then chemical reactions occur and are consumed.Ozone mainly reacts with the active radicals contained in HOX, NOX, ClOX and BrOX in the same gas phase.[4]
Causes of ozone layer destruction
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As for the reasons for the change and destruction of the ozone layer, it is generally believed thatSolar radiation intensityChange, the change of atmospheric temperature field and pressure field caused by atmospheric movement, as well as the movement and transportation of chemical components related to ozone generation will affect the photochemical balance of ozone, thus affecting the concentration and distribution of ozone.The introduction of chemical reactants will directly participate in the reaction and have a greater impact on ozone concentration.The impact of human activities, mainly in terms ofOzone Depleting SubstancesProduction, consumption and emissions.
Encyclopedia x ignorance: diagram of ozone layer depletion
Ozone in the atmosphere can react with many substances and be consumed and destroyed.Among all substances that react with ozone, the simplest and most active are chemical substances containing carbon, hydrogen, chlorine and nitrogen, such as nitrous oxide (NtwoO) , steam (HtwoO) , carbon tetrachloride (CClfour）, Methane (CHfour）And chlorofluorocarbons (CFCs), which are now the most important.These substances are normally stable in the lower atmosphere, but become ozone depleting substances after the stratosphere is activated by ultraviolet radiation.This reaction consumes ozone in the stratosphere, breaks the balance of ozone, and leads to the increase of ground ultraviolet radiation, thus bringing a series of problems to the earth's ecology and human beings.[5]
Impact of ozone layer destruction
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After the ozone layer is largely depleted, its ability to absorb ultraviolet radiation is greatly weakened, leading to the obvious increase of ultraviolet B reaching the earth's surface, which will give human health andecological environmentIt has brought many hazards, which have been widely concerned by people, mainly on human health, terrestrial plants, aquaticecosystem, biochemical cycle, materials, tropospheric atmospheric composition and air quality.
Impact on human health
The reduction of ozone and the destruction of the ozone layer increase the amount of ultraviolet radiation reaching the ground.Among them, the UV-B ultraviolet band increases more.The increase of UV-B ultraviolet radiation will have a great impact on human health.Relevant research shows that UV has no other beneficial effects except VD in human skin.Ultraviolet radiation is harmful to human body.It mainly affects human skin, eyes andimmune system。
Experiments prove that ultraviolet rays can damageCornealAnd eye lens, such as causing cataract, eye lens deformation, etc.According to analysis, if stratospheric ozone decreases by 1%, the incidence of cataracts in the world will increase by 0.6-0.8%, and the number of blindness caused by cataracts in the world will increase by 10000 to 15000;If no measures are taken to increase ultraviolet radiation, the increase of UV-B radiation will lead to about 18 million cataract cases by 2075.
The increase of UV - B segment can obviously induce three skin diseases that human often suffer from.Of the three skin diseases,Basel Dermatoma and squamous dermatoma are non malignant.The latest research results obtained from animal experiments and human epidemiological data show that if the ozone concentration drops by 10%, the incidence of non malignant skin tumors will increase by 26%.Another malignant melanoma is a very dangerous skin disease. Scientific research has also revealed the internal relationship between UV-B ultraviolet rays and the incidence of malignant melanoma, which is especially serious for people with light skin color, especially in childhood;
Human immune systemPart ofimmune systemIt can be directly exposed to ultraviolet radiation.Animal experiments have found that ultraviolet radiation can reduce the immune response of human body to skin cancer, infectious diseases and other antigens, thus leading to the loss of immune response to repeated external stimuli.Human research results also show that exposure to ultraviolet B will inhibit immune response, and the importance of these immune responses to infectious diseases in the human body is not very clear.However, in some areas of the world where infectious diseases have a greater impact on human health and among people with incomplete immune function, the increased UV-B radiation has a considerable inhibitory effect on immune response.
Previous studies have shown that long-term exposure to strong ultraviolet radiation will lead to changes in DNA in cells,Human immune systemThe human body's ability to resist diseases declines.This will worsen the already poor health conditions of many developing countries, and increase the incidence and severity of a large number of diseases, especiallymeasles、Chicken pox、herpesAnd other viral diseases,malariaAnd so on through the skinParasitosis，pulmonary tuberculosisandLeprosyBacterial infection and fungal infection.[2]
Impact on biology
Although plants have developed a protective mechanism against high levels of UV-8, experimental studies show that their strain capacity increases significantly at the wavelength of 280 ～ 320nm.Up to now, more than 200 different plants have been tested for UV sensitivity at wavelengths of 280~320nm, and it is found that 2/3 of them have reacted.Sensitive species such as cotton, pea, soybean, melon and cabbage are found to grow slowly, and some pollen cannot germinate.It can damage plant hormones and chlorophyll, thus reducing photosynthesis.[2]
Impact on global climate
Ozone in the stratosphere has two opposite effects on climate regulation. If the concentration of ozone in the stratosphere decreases, the ultraviolet radiation absorbed here will be correspondingly reduced, and the stratosphere itself will become cold, so the infrared radiation released will be reduced, which will make the earth cool.On the other hand, as the amount of ultraviolet radiation radiated to the ground increases, the earth will warm up.If the reduction of ozone concentration in the whole stratosphere is uniform, the above two effects can offset each other, but if the reduction of ozone concentration in different regions of the stratosphere is inconsistent, the two effects will not offset each other.The current situation is that the stratospheric ozone layer is decreasing unevenly. The net effect of this change has yet to be further confirmed by scientific research.[5]
Countermeasures for ozone layer protection
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The danger caused by ozone reduction has been widely concerned by the international community. In order to protect the ozone layer from destruction and better protect the ecological environment, the international action to protect the ozone layer has lasted for more than 20 years.
1. Establish international and national legal binding mechanisms for ozone layer protection to control the emissions of ozone depleting substances.
The Plan for the Protection of the Ozone Layer has been adopted internationally《Vienna Convention for the Protection of the Ozone Layer》Montreal Protocol on Substances that Deplete the Ozone Layer.China signed the London Amendment to the Protocol in June 1991. At present, there are 168 parties to the Protocol.In 1994, the 52nd United Nations General Assembly decided to set September 16 asInternational Day for the Protection of the Ozone Layer。China is working hard to achieve the targets set by the Protocol, and has formulated and implemented more than 20 policies related to the protection of the ozone layer.This reducesOzone Depleting SubstancesThe concentration and protection of the ozone layer are of great significance.
2. Strengthen the research and development of freon substitutes
The development of alternatives to Freon has received extensive attention. At present, it mainly includes hydrogen containing Freon, whose convection circle is decomposed before reaching the ozone layer.Or use non chlorine Freon, such as F32, F215, F134a and F143, even if they reach the ozone layer, they will not cause damage.Some substitutes are organics without F and Cl, such as refined petroleum gas and dimethyl ether, alkanes, nitrogencarbon dioxideEtc.In addition, research on the recovery and decomposition of HCFCs is also ongoing.
3. Raise awareness of protecting the ozone layer and firmly establish environmental awareness
Although human beings try to find another planet that is close to the earth and can be used for human survival, they have to admit that the earth is still the only home of human beings, and people cannot survive without the earth.Therefore, we must treat the earth and nature well. We must not focus on the speed and quantity of development at the expense of the environment.On the contrary, we should emphasize the harmony between man and nature, emphasize the sustainable use of resources, understand the role of the ozone layer, enhance the awareness of ecological environment, and jointly safeguard the earth.[2]
Current status of ozone layer protection
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Existing crisis
Because ozone has its special nature and is vulnerable to various factors, the ozone layer is very fragile.Satellite observation data show that since the 1970s, the total amount of global ozone has decreased significantly. From 1979 to 1990, the total amount of global ozone decreased by about 3%.The amount of ozone in the vicinity of the Antarctic is particularly serious, about 30%~40% lower than the global average ozone, and the "Antarctic ozone hole" appears.Since the discovery of the "ozone hole" in 1985, it has become both wide and deep in 1987. Although it eased in 1988, a strong "ozone hole" appeared every spring in the southern hemisphere from 1989 to the first few years of the 1990s, and the Antarctic ozone hole was still expanding from 1994 to 1996.Recently, according to the data sent back by the detectors installed on Russian and American satellites, the "Antarctic Ozone Hole" has an area of 2400 square kilometers, and the thinnest part is only more than 100 bushen units (100 dobson, equivalent to 1 mm thick).[5]
Recovery results
On September 12, 2014, NASA scientist Paul Newman, who was responsible for the ozone level assessment for the past four years, said that from 2000 to 2013, the ozone level at the altitude of 50 kilometers in the mid northern latitudes had risen by 4%.Scientists attribute this positive change to the global restrictions on the use of certain refrigerants and foaming agents, and also show that as long as global action is taken, humans can resist or delay the ecological crisis.The United Nations organizes 300 scientists to continuously monitor the Earth's ozone level, with an assessment period of every four years.In addition, although the ozone layer is recovering, it is still far from recovery.The Antarctic ozone hole still exists. The latest calculation shows that the ozone concentration level is still 6% lower than that in 1980.It was previously predicted that the Antarctic ozone hole might disappear completely before 2065.According to the latest data, Achim Steiner, Executive Director of the United Nations Environment Project, judged that the ozone layer may recover in the middle of this century, but it still depends on the joint efforts of all countries.
On September 10, 2014,world meteorological organizationAndUnited Nations Environment ProgrammeThe report said that the earth's ozone layer is expected to recover in the coming decades.The summary version of the 2014 Scientific Assessment Report on Ozone Layer Depletion released by the two organizations on the same day pointed out that the Montreal Protocol reached by the international community in 1987 was not intended to reduceOzone Depleting SubstancesHas made a great contribution.Actions based on the Protocol and related agreements have successfully reduced the amount ofCFCsAnd halons in the atmosphere.
The report points out that if the Montreal Protocol can be fully complied with, the ozone layer over the mid latitude region and the Arctic is expected to return to the 1980 baseline level (the level before the serious depletion of the ozone layer) by the middle of this century, and some parts of the Antarctic are expected to return to this level later.[6]
