Knowledge about the ozone layer
Knowledge about the ozone layer
the formation of the ozone layer， the role of the ozone layer， the causes of the destruction of the ozone layer， the impact of the destruction of the ozone layer， the countermeasures for the protection of the ozone layer，and the current status of the protection of the ozone layer.
Ozone layer
The ozone layer is the high concentration of ozone 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 adjusted to the standard, its thickness is only about 3 mm on average. The ozone content varies with latitude, season and weather. Ultraviolet radiation is absorbed by ozone at high altitudes and has a warming effect on the atmosphere. At the same time, it protects the creatures on the earth from the damage of far ultraviolet radiation. The small amount of ultraviolet radiation passed through has a bactericidal effect and is of great benefit to organisms.
The discovery of ozone
Humans really knew about ozone more than 150 years ago. Dr. Schanbein (Germany) first proposed that the odor produced by water electrolysis and spark discharge is the same as that produced by lightning in nature. Dr. Schanbein believes that the odor is difficult. Smell, hence the name ozone. The ozone layer was discovered by French scientist Fabry in the early 20th century. In 1930, British geophysicist Kapman proposed that ozone in the atmosphere is mainly produced by the three-body collision between oxygen atoms and oxygen molecules with the participation of a third neutral molecule. At an altitude above 60 kilometers, the sun’s ultraviolet rays are strong, oxygen molecules are dissociated in a large amount, the chance of three-body collisions is reduced, and the ozone content is very small. At low altitudes below 5 kilometers, the ultraviolet rays are greatly weakened, and there are few oxygen atoms, making it difficult to form ozone. Within the height range of 20-25 kilometers, there are enough oxygen atoms and enough oxygen molecules, which is most conducive to the three-body collision, and the ozone formed is about 50 billion tons per year. To
Ozone formation
Ozone in nature is mostly distributed in the atmosphere 20Km-50Km above the ground, which we call 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 long-wave and short-wave. When the oxygen molecules in the atmosphere (containing 21%) are irradiated with short-wave ultraviolet rays, the oxygen molecules will decompose into atomic states. Oxygen atoms are extremely unstable and easily react with other substances. For example, it reacts with hydrogen (H2) to produce water (H2O), and reacts with carbon (C) to produce carbon dioxide (CO2). Similarly, when it reacts with oxygen molecules (O2), ozone (O3) is formed. 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. As the temperature changes (rise) during the fall process, the instability of ozone becomes more and more obvious, and it is again irradiated by long-wave ultraviolet rays and reduced to oxygen. The ozone layer maintains this dynamic balance of the mutual conversion of oxygen and ozone. To
Time and space changes
The total amount of ozone in the earth’s atmosphere has obvious temporal and spatial changes: the lowest near the equator and the highest near 60° latitude; the largest in any region in spring and the smallest in autumn; the ozone content is usually higher at night than during the day; in mid-latitudes of Asia When the Siberian air mass invaded, the total amount of ozone increased significantly, but when the equatorial air mass came, its total amount decreased. Nearly 1% of the sun’s ultraviolet rays reach the ground. Especially in the forests, mountains, and coasts where the air pollution is relatively light, there are more ultraviolet rays, and there is relatively rich ozone.
Ozone layer action
The atmospheric ozone layer has three main functions.
One is protection. The ozone layer can absorb ultraviolet rays below 306.3nm in the sunlight, mainly part of UV-B (wavelength 290～300nm) and all UV-C (wavelength <290nm=, protecting humans and Animals and plants are protected from short-wave ultraviolet rays. Only long-wave ultraviolet rays UV-A and a small amount of medium-wave ultraviolet rays UV-B can radiate to the ground. Long-wave ultraviolet rays are much less harmful to biological cells than medium-wave ultraviolet rays. So the ozone layer is like a piece The umbrella protects the creatures on the earth to survive and multiply.
The second is heating. Ozone absorbs ultraviolet rays from sunlight and converts it into heat to heat the atmosphere. Due to this effect, the atmospheric temperature structure has a peak at a height of about 50km, and there is a heating layer 15-50km above the earth. It is precisely because of the presence of ozone that the stratosphere exists. As there is no ozone and oxygen on planets other than the earth, there is no stratosphere. The temperature structure of the atmosphere has an important influence on the circulation of the atmosphere, and the cause of this phenomenon also comes from the high distribution of ozone.
The third is the role of greenhouse gases. In the upper troposphere and the bottom of the stratosphere, that is, at the altitude where the temperature is very low, the role of ozone is also very important. If the ozone at this height is reduced, it will generate momentum to lower the surface temperature. Therefore, the height distribution and changes of ozone are extremely important.
The ozone in the stratosphere absorbs a large amount of ultraviolet radiation (240-329 nanometers, called UV-B wavelength) emitted by the sun that is harmful to humans, animals and plants, and provides a barrier for the earth to prevent the harmful effects of ultraviolet radiation. But on the other hand, ozone spreads all over the troposphere, but it plays a detrimental role in greenhouse gases. The ozone depletion in the stratosphere is mainly caused by dynamic migration to the troposphere, where most of the substrate and carrier molecules with active catalysis are obtained, and then chemical reactions occur and are consumed. Ozone mainly reacts with the active free radicals contained in HOX, NOX, ClOX, and BroX.
Causes of Ozone Destruction
Regarding the causes of changes and destruction of the ozone layer, it is generally believed that changes in solar radiation intensity caused by solar activity, changes in atmospheric temperature and pressure fields caused by atmospheric movement, and the movement and transportation of chemical components related to ozone production will all affect the photochemistry of ozone. The balance affects the concentration and distribution of ozone. The introduction of chemical reactants will directly participate in the reaction and have a greater impact on the 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 react with many substances to be consumed and destroyed. Among all the substances that react with ozone, the simplest and most active are chemical substances containing carbon, hydrogen, chlorine and nitrogen, such as nitrous oxide (N2O), water vapor (H2O), tetrachloride Carbon (CCl4), methane (CH4) and chlorofluorocarbons (CFC) which are now the most important. These substances are stable under normal conditions in the lower atmosphere, but become ozone-depleting substances when the stratosphere is activated by ultraviolet radiation. This reaction consumes the ozone in the stratosphere, breaks the balance of ozone, and leads to an increase in ultraviolet radiation on the ground, which brings a series of problems to the earth's ecology and humans.
Ozone depletion impact
After the ozone layer is largely depleted, the ability to absorb ultraviolet radiation is greatly reduced, resulting in a significant increase in ultraviolet B reaching the surface of the earth, which brings many harms to human health and the ecological environment. The main issues that have received general attention are human health, The impact of terrestrial plants, aquatic ecosystems, biochemical cycles, materials, and tropospheric atmospheric composition and air quality.
Impact on human health
The decrease in the amount 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 has increased more. The increase of UV-B ultraviolet radiation will have a great impact on human health. Relevant studies have shown that ultraviolet rays have not found other beneficial effects except for the production of VD in human skin. Ultraviolet rays are more harmful to the human body. It mainly affects human skin, eyes and immune system.
Experiments have proved that ultraviolet rays can damage the cornea and eye lens, such as causing cataracts and lens deformation. According to analysis, if the stratospheric ozone is reduced by 1%, the global incidence of cataracts will increase by 0.6-0.8%, and the number of blindness caused by cataracts in the world will increase by 10,000 to 15,000; if measures are not taken to increase ultraviolet rays, by 2075, The increase in UV-B radiation will cause approximately 18 million cases of cataracts.
The increase of ultraviolet UV-B segment can obviously induce three kinds of skin diseases that humans often suffer from. Of these three skin diseases, Basel skin tumor and squamous skin tumor 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 skin tumors will increase by 26%. Another type of malignant melanoma is a very dangerous skin disease. Scientific research has also revealed the internal link between UV-B ultraviolet rays and the incidence of malignant melanoma. This hazard is particularly serious for light-skinned people, especially in childhood;
Part of the human immune system exists 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 antigens, which in turn leads to the loss of immune response to repeated external stimuli. Human research results also show that exposure to ultraviolet B will inhibit the 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 people with imperfect immune functions, increased UV-B radiation has a considerable impact on the suppression of immune responses.
Studies have shown that long-term exposure to strong ultraviolet radiation can cause DNA changes in cells, the function of the body's immune system declines, and the body's ability to resist diseases decreases. This will worsen the poor health of many developing countries, and the incidence and severity of a large number of diseases will increase, especially viral diseases such as measles, chickenpox, herpes, and malaria and other parasitic diseases transmitted through the skin. , Bacterial infections such as tuberculosis and leprosy, and fungal infections. To
Impact on biology
Although plants have developed a protective mechanism against the high levels of UV-8, experimental studies have shown that their ability to respond to increased strain at the wavelength of 280-320 nanometers differs greatly. So far, more than 200 different plants have been tested for ultraviolet sensitivity with a wavelength of 280-320 nanometers, and two-thirds of them have been found to respond. Sensitive species such as cotton, peas, soybeans, melons and cabbage are found to grow slowly and some pollen cannot germinate. It can damage plant hormones and chlorophyll, thereby reducing photosynthesis.
Impact on global climate
The 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 colder, so that the infrared radiation emitted will be reduced. , Because it will make the earth cold. On the other hand, the increase in the amount of ultraviolet radiation radiated to the ground will warm the earth. If the decrease in 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 an uneven reduction trend. The net effect of this change remains to be further confirmed by scientific research. To
Ozone layer protection measures
The danger caused by ozone reduction has been widely concerned by the international community. In order to protect the ozone layer from destruction and to better protect the ecological environment, international actions to protect the ozone layer have continued for more than 20 years.
1. Establish international and national legal binding mechanisms for the protection of the ozone layer to control the emission of ozone-depleting substances.
Internationally, the "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. my country signed the London Amendment to the "Protocol" in June 1991. At present, there are 168 parties to the "Protocol". In 1994, the 52nd UN General Assembly decided to designate September 16 each year as the International Day for the Protection of the Ozone Layer. Our country 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 is of great significance for reducing the concentration of ozone-depleting substances and protecting the ozone layer.
2. Strengthen the research and development of freon substitutes
The development of alternatives to Freon has received extensive attention. At present, it mainly includes Freon containing hydrogen, which 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 alternatives are organic substances that do not contain F and Cl, such as refined petroleum gas and dimethyl ether, alkanes, nitrogen, and carbon dioxide. In addition, research work on the recovery and decomposition of HCFCs is also underway.
3. Raise awareness of protecting the ozone layer and firmly establish environmental awareness
Although mankind is trying to find another planet that is close to the earth and can be used for human existence, it has to be admitted that the earth is still the only home for mankind, and human beings will not survive without the earth. Therefore, we must treat the earth and nature well, and we must not one-sidedly emphasize the speed and quantity of development at the expense of the environment. On the contrary, it should emphasize the harmony between man and nature, emphasize the continuous use of resources, understand the role of the ozone layer, enhance the awareness of the ecological environment, and jointly safeguard the earth.
Current status of ozone layer protection
Existing crisis
Because ozone has its special properties and is easily affected by 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 dropped by roughly 3%. The decrease in ozone near the Antarctic is particularly serious, about 30% to 40% lower than the global ozone average, and an "Antarctic ozone hole" has appeared. Since the discovery of the "ozone hole" in 1985, it became wide and deep in 1987. Although it eased in 1988, from 1989 to the first few years of the 1990s, a strong "ozone hole" appeared every spring in the southern hemisphere. "From 1994 to 1996, the Antarctic ozone hole was still expanding. Recently, data sent back from detectors installed on Russian and American satellites have learned that the area of the "Antarctic ozone hole" has reached 2,400 square kilometers, and the thinnest point is only 100 Dobson units (100 dobson, equivalent to 1 millimeter thickness). To
Restore results
On September 12, 2014, NASA scientist Paul Newman, who was responsible for the assessment of ozone levels for the past four years, said that from 2000 to 2013, the ozone level at an altitude of 50 kilometers in the central and northern latitudes had risen by 4%. Scientists attribute this positive change to global restrictions on the use of certain refrigerants and foaming agents, and at the same time show that as long as global action is required, humans can resist or delay the ecological crisis. 300 scientists of the United Nations organize continuous monitoring of the earth's ozone level, and an evaluation period is made every 4 years. In addition, although the ozone layer is recovering, it is still far away from recovery. The Antarctic ozone hole still exists, and the latest calculations show that the ozone concentration level is still 6% lower than in 1980. It was previously predicted that the Antarctic ozone hole may disappear completely before 2065. According to the latest data, the executive director of the United Nations Environment Project, Achim Steiner, judges that the ozone layer may heal in the middle of this century, but it still needs to rely on the joint efforts of all countries.
On September 10, 2014, the World Meteorological Organization and the United Nations Environment Programme issued a report stating that the earth’s ozone layer is expected to be restored in the next few decades. The summary version of the "2014 Scientific Assessment Report on Ozone Depletion" issued by the two organizations on the same day pointed out that the Montreal Protocol reached by the international community in 1987 has made a great contribution to reducing the emissions of ozone-depleting substances. Actions based on the Protocol and related agreements have successfully reduced。
