The ozone layer is a layer with high ozone concentration in the stratosphere of the atmosphere. The most concentrated part is located at an altitude of 20-25 kilometers. If the ozone of the ozone layer is calibrated to the standard case, its thickness is only about 3 mm on average.
Ozone content varies with latitude, season, and weather. Ultraviolet radiation is absorbed by ozone at a high altitude, which has a warming effect on the atmosphere, and at the same time protects living things on the earth from far-ultraviolet radiation. The small amount of ultraviolet radiation transmitted has a bactericidal effect and is of great benefit to living things.
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Introduction of Ozone Layer
Humans really know about ozone more than 150 years ago. Dr. Schanbein of Germany first proposed that the odor produced in water electrolysis and spark discharge was the same as that produced after lightning in nature. The smell, hence the name ozone.
The ozone layer was discovered by French scientist Fabry in the early 20th century. In 1930, British geophysicist Chapman proposed that the ozone in the atmosphere is mainly generated by oxygen atoms and oxygen molecules, which are produced by a three-body collision with the participation of the third type of neutral molecule.
At an altitude of more than 60 kilometers, the sun’s ultraviolet rays are strong, a large number of oxygen molecules are dissociated, the chance of a three-body collision is reduced, and the ozone content is extremely small.
At low altitudes below 5 kilometers, ultraviolet rays are greatly weakened, and there are few oxygen atoms, making it difficult to form ozone. In the range of 20 to 25 kilometers, there are enough oxygen atoms and enough oxygen molecules, which is most conducive to the collision of three bodies. The ozone formed is about 50 billion tons per year.
Form of Ozone Layer
Ozone in nature is mostly distributed in the atmosphere from 20Km to 50Km above the ground. We call it the ozone layer. The ozone in the ozone layer is mainly produced by ultraviolet rays.
The ultraviolet rays in the sun’s rays are divided into two types: a long wave and short wave. When oxygen molecules in the atmosphere (containing 21%) are irradiated with short wave ultraviolet rays, the oxygen molecules will be decomposed into atomic states.
The oxygen atom is extremely unstable and easily reacts with other substances. Such as reaction with hydrogen (H2) to produce water (H2O), and reaction with carbon (C) to produce carbon dioxide (CO2). Similarly, when reacting with oxygen molecules (O2), ozone (O3) is formed. After the formation of ozone, its specific gravity is higher than that of oxygen, and it will gradually descend to the bottom of the ozone layer.
During the descent, as the temperature changes (rises), the ozone instability becomes more and more obvious. After being exposed to long-wave ultraviolet rays, it is reduced again to oxygen. The ozone layer maintains the dynamic balance of this conversion between oxygen and ozone.
The total amount of ozone in the Earth’s atmosphere has obvious spatial and temporal changes: it is the lowest near the equator and the highest near latitude 60° any area is the largest in spring and the smallest in autumn.
The ozone content is usually higher at night than during the day in a day, in the middle latitudes of Asia When the Siberian air mass invaded, the total amount of ozone increased significantly, and when the equatorial air mass came, its total amount decreased.
About 1% of the ultraviolet rays from the sun reach the ground. Especially in forests, mountains, and coasts where air pollution is light, there are more ultraviolet rays and there is relatively abundant ozone.
Ozone Layer Effect
The atmospheric ozone layer has three main functions. One is protection. The ozone layer can absorb sunlight.
The ultraviolet rays with a wavelength below 306.3nm are mainly a part of UV-B (wavelength 290-300nm) and all UV-C (wavelength <290nm =, which protects humans, animals and plants on the earth from short-wave ultraviolet rays.
Only long waves Ultraviolet UV-A and a small amount of medium-wave ultraviolet UV-B can radiate to the ground. Long-wave ultraviolet damages biological cells much less than medium-wave ultraviolet. Therefore, the ozone layer is like an umbrella to protect the life on the earth.
The second is heating. Ozone absorbs ultraviolet rays from sunlight and converts them into thermal energy to heat the atmosphere. Due to this effect, the atmospheric temperature structure has a peak at a height of about 50km, and a warming layer exists 15 to 50km above the earth.
It is because of the existence of ozone that the stratosphere exists. Since planets other than Earth do not have ozone and oxygen, there is no stratosphere. The temperature structure of the atmosphere has an important effect on the circulation of the atmosphere.
The cause of this phenomenon also comes from the high distribution of ozone.
The third is the effect of greenhouse gases. The effect of ozone is also very important in the upper troposphere and the bottom of the stratosphere, that is, at the altitude where the temperature is very low. If this level of ozone is reduced, it will generate power to reduce the ground temperature.
Therefore, the height distribution and change of ozone are extremely important.
The ozone in the stratosphere absorbs a large amount of ultraviolet radiation (240-329 nm, called UV-B wavelength) emitted by the sun, which is harmful to humans, animals, and plants, and provides a barrier for the earth to prevent the harmful effects of ultraviolet radiation.
On the other hand, ozone is spread throughout the troposphere, but it has an adverse effect on greenhouse gases. Ozone depletion in the stratosphere is mainly through dynamic migration to the troposphere, where most of the substrates and carrier molecules with active catalysis are obtained, which are consumed by chemical reactions. Ozone mainly reacts in the same family with the active radicals contained in HOX, NOX, ClOX, and Brox.
Causes of Ozone Destruction
Regarding the causes of the change and destruction of the ozone layer, it is generally believed that changes in the intensity of solar radiation caused by solar activity, changes in atmospheric temperature and pressure fields caused by atmospheric motion, and the movement and transport of chemical components related to ozone generation will all affect the photochemistry of ozone Equilibrium affects 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 is mainly manifested in the production, consumption, and emission of ozone-depleting substances.
The ozone in the atmosphere can be consumed and destroyed by reacting with many substances. Of all the substances that react with ozone, the simplest and most active are chemicals containing carbon, hydrogen, chlorine, and nitrogen, such as nitrous oxide (N2O), water vapor (H2O), tetrachloride Carbon (CCl4), methane (CH4), and chlorofluorocarbon (CFC), which is currently the most important.
These substances are normally stable in the lower atmosphere, but they become ozone-depleting substances after being activated by ultraviolet radiation in the stratosphere.
This reaction consumes ozone in the stratosphere, breaks the ozone balance, and causes an increase in ground ultraviolet radiation, which causes a series of problems for the earth’s ecology and humanity.
Impact of ozone Layer Destruction
After a large amount of ozone layer is depleted, the ability to absorb ultraviolet radiation is greatly weakened, resulting in a significant increase in ultraviolet Breaching the earth’s surface, which brings various harm to human health and the ecological environment. Impacts of terrestrial plants, aquatic ecosystems, biochemical cycles, materials, and tropospheric atmospheric composition and air quality.
Impact on Human Health
Decreasing the amount of ozone and destroying the ozone layer increases the amount of ultraviolet radiation reaching the ground. Among them, UV-B ultraviolet waveband increases more.
The increase of UV-B radiation will have a great impact on human health. Related research shows that, in addition to VD in human skin, no other beneficial effects have been found.
Ultraviolet is harmful to the human body. It mainly affects the human skin, eyes, and immune system.
Experiments have shown that ultraviolet rays can damage the cornea and eye lenses, such as causing cataracts and deforming eyeball lenses.
According to analysis, a 1% reduction in stratospheric ozone will increase the incidence of cataracts worldwide by 0.6-0.8%. The number of blindness caused by cataracts worldwide will increase by 10,000 to 15,000, if measures are not taken to increase the ultraviolet rays, by 2075, Increased UV-B radiation will cause approximately 18 million cataract cases.
The increase of the ultraviolet UV-B segment can obviously induce three kinds of skin diseases that humans often suffer from. Of the three skin diseases, Basel dermatome and squamous dermatome are non-malignant. The latest research results using animal experiments and human epidemiological data show that if the ozone concentration drops by 10%, the incidence of non-malignant dermatomes will increase by 26%. Another type of malignant melanoma is a very dangerous skin disease.
Scientific research has also revealed the intrinsic relationship between UV-B segment ultraviolet rays and the incidence of malignant melanoma. This harm is particularly serious for light-skinned people, especially in childhood;
A part of the body’s immune system resides in the skin, making the immune system directly exposed to ultraviolet radiation.
Animal experiments have found that ultraviolet radiation can reduce the body’s immune response to skin cancer, infectious diseases, and other antigenic bodies, leading to a loss of immune response to repeated external stimuli.
The results of human studies have also shown that exposure to ultraviolet B can suppress the immune response, and the importance of these immune responses to infectious diseases in humans is not very clear.
However, in some regions of the world where infectious diseases have a greater impact on human health and people with inadequate immune functions, increased UV-B radiation has a significant impact on the suppression of immune responses.
Previous studies have shown that long-term exposure to strong ultraviolet radiation can cause changes in DNA in cells, reduce the function of the human immune system, and reduce the body’s ability to resist disease.
This will allow many developing countries should not have a good state of health worsened, a large number of disease incidence and severity will increase, especially including measles, chickenpox, herpes, and other viral diseases, malaria and other skin infections by parasitic disease, Bacterial infections such as tuberculosis and leprosy, and fungal infections.
Impact on Living Things
Although plants have developed protective mechanisms against high levels of UV-8, experimental studies have shown that they have very different strain capacities for increased levels of wavelengths from 280 to 320 nanometers.
So far, more than 200 different plants have been tested for UV sensitivity at a wavelength of 280 to 320 nm, and 2/3 of them have responded. Sensitive species such as cotton, peas, soybeans, melon, and cabbage have been found to grow slowly and some pollen cannot germinate. It can damage plant hormones and chlorophyll, thereby reducing photosynthesis.
Impact on the global climate
The ozone in the stratosphere has two opposite effects on climate regulation. If the ozone concentration in the stratosphere is reduced, the ultraviolet radiation absorbed here will be reduced accordingly, and the stratosphere itself will be cooled, so the infrared radiation released will be reduced, which will cool the earth.
On the other hand, as the amount of ultraviolet radiation radiated to the ground increases, the planet will become warmer and warmer. If the reduction of the ozone concentration in the entire stratosphere is uniform, the above two effects can cancel each other out, but if the ozone layer concentration decreases in different regions of the stratosphere are inconsistent, the two effects will not cancel each other out.
The current situation is that the reduction of the stratospheric ozone layer shows a trend of uneven reduction. The net effect of this change has yet to be confirmed by scientific research.
Ozone layer protection measures
The dangers caused by ozone reduction have received widespread attention from the international community. In order to protect the ozone layer from damage and better protect the ecological environment, international efforts to protect the ozone layer have continued for more than 20 years.
1. Establish international and national legal mechanisms for ozone layer protection to control the emissions of substances that destroy the ozone layer.
The International Plan for the Protection of the Ozone Layer, the Vienna Convention for the Protection of the Ozone Layer, and the Montreal Protocol on Substances that Deplete the Ozone Layer have been adopted internationally.
2. Strengthen the research and development of Freon substitutes
The development of Freon alternatives has received extensive attention. Currently, it mainly includes hydrogen-containing Freon, whose convection ring is decomposed before reaching the ozone layer.
Or use Freon without chlorine, such as F32, F215, F134a, and F143, etc., even if they reach the ozone layer, they will not cause damage. Some alternatives are organic compounds that do not contain F and Cl, such as refined petroleum gas and dimethyl ether, alkanes, nitrogen, carbon dioxide, and so on. In addition, research work 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 are trying to find another planet that is close to the earth and can be used by human beings, we have to admit that the earth is still the only home of mankind, and people will not survive without it.
Therefore, we must be kind to the earth and nature. We must not emphasize 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, recognize the role of the ozone layer, enhance the awareness of the ecological environment, and jointly safeguard the planet.
Ozone Layer Protection Status
Ozone is very fragile because of its special properties and its susceptibility to various factors. Satellite observations show that since the 1970s, the total amount of global ozone has decreased significantly. From 1979 to 1990, the total amount of global ozone dropped by approximately 3%.
The reduction of ozone near Antarctica is particularly serious, about 30% to 40% below the global average ozone, and an “Antarctic ozone hole” has appeared. Since the discovery of the “ozone hole” in 1985, it has become wide and deep by 1987.
Although it eased in 1988, a strong “ozone hole” appeared in the spring in the southern hemisphere every year from 1989 to the first few years of the 1990s. “The ozone hole in Antarctica continued to expand from 1994 to 1996.
Recently, it was learned from data sent back by detectors installed on Russian and US satellites that the “Antarctic ozone hole” has reached an area of 2,400 square kilometers, with only 100 Dobson units at its thinnest point (100 dobsons, equivalent to 1 mm thickness).
Recovery Results of Ozone Layer
On September 12, 2014, NASA scientist Paul Newman, responsible for ozone level assessment in the past four years, said that from 2000 to 2013, ozone levels at 50 km altitude in the mid-north latitudes had risen by 4%.
Scientists attribute this positive change to global restrictions on the use of certain refrigerants and foaming agents and explain that as long as global action is taken, humans can resist or delay the ecological crisis.
300 scientists from the United Nations Organization continuously monitor the earth’s ozone levels, with an assessment period every 4 years. In addition, although the ozone layer is recovering, it is still far from being cured.
The Antarctic ozone layer still exists, and the latest calculations show that the ozone concentration level is still 6% lower than in 1980. Previous predictions have suggested that the Antarctic ozone layer hole may completely disappear by 2065.
According to the latest data from the executive director of the United Nations Environment Program, Achim Steiner, the ozone layer may be recovered in the middle of this century, but it still needs the joint efforts of all countries.
On September 10, 2014, the World Meteorological Organization and the United Nations Environment Programme released a report saying that the earth’s ozone layer is expected to be restored in the next few decades.
The summary version of the Scientific Assessment Report on Ozone Depletion 2014 released by the two organizations on the same day pointed out that the Montreal Protocol reached by the international community in 1987 made a significant contribution to reducing the emissions of ozone-depleting substances.
Actions based on the protocol and related agreements have succeeded in reducing the atmospheric abundance of gases such as CFCs and halons that have been used in products such as refrigerators, sprayers, insulating foam and fire extinguishers.
The report states that if the Montreal Protocol is fully complied with, the ozone layer over mid-latitudes and the Arctic is expected to return to the 1980 baseline level (the level before the ozone layer was severely depleted) by the middle of this century, and parts of the Antarctic are expected to be later Time to return to this level.