Shulou(Shulou.com)12/24 Report--

Note: this article is about 4600 words and the reading time is about 15 minutes.

The ozone layer hole (Ozone depletion) over Antarctica has aroused widespread concern at the social level. However, in recent years, news about the hole in the ozone layer has been rarely mentioned. Are human beings numb in the face of disasters? Of course not. On January 9 this year, the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) vividly explained to us what is meant by "making a fortune in silence". They released an exciting piece of good news:

It is expected that the TCO (total ozone column) in Antarctica will return to the 1980 level around 2066, while the TCO in the Arctic will return to the 1980 level around 2045, which is close to the global average level (60 °N ~ 60 °S) and return to 1980 level around 2040.

It's like a hole in the ozone layer saying, "I'm going to shrink quietly and surprise everyone."

(change in the range of the maximum ozone hole in 1979-2019) this is a historic moment when mankind, through global efforts, is about to solve this major climate crisis related to the survival of human civilization for the first time.

What is the ozone layer? Why is the ozone hole so important? How do humans repair the hole in the ozone layer? In this way, problems that we only knew but did not understand in the past are all explained clearly at one time today.

(ozone hole changes in 1960-2100) 1. What is the ozone layer? The earth's atmosphere is extremely thick, totaling thousands of kilometers. From bottom to top, it can be divided into troposphere (0~10/20km), stratosphere (10/20~50km), mesosphere (50~85km), thermal layer (85~800km) and escape layer (800~3000km).

The troposphere is the closest part of the atmosphere to the surface, covering almost the entire biosphere, and is the environment in which we humans and other organisms live; at the same time, it is also the densest atmosphere, with a total mass of about 75% of the total atmospheric mass. The temperature of the troposphere mainly comes from the surface, showing a hot and cold situation, the upper and lower convection movement is very active, so it is called the troposphere.

The stratosphere begins about 10-15 kilometers (km) above the earth's surface and extends to an altitude of about 50 kilometers. Unlike the troposphere, the lower stratosphere is cold and hot, so the air flow in this layer is very stable. The stratospheric characteristics make it very suitable for aircraft operation, so the horizontal flight phase of most civil aircraft is at the bottom of the stratosphere.

The reason for the nature of the stratosphere is related to the ozone layer, the protagonist of our article. Most ozone (about 90%) exists in the stratosphere, and the area with the highest ozone concentration, about 15 to 35 km above sea level, is often referred to as the "ozone layer". The ozone layer absorbs most of the heat from ultraviolet rays, heating the upper stratosphere, thus causing the emergence of the stratosphere.

As for the mesosphere, thermal layer and escape layer, they are too far away from us and have become the research category of space science in scientific research.

The ozone layer refers to the stratospheric layer with high ozone concentration, and its peak concentration appears at the height of about 20~25km. Although the ozone layer is called the layer, its abundance is still relatively low, even in the region with the highest concentration of the ozone layer, there are only a few thousand ozone molecules per billion air molecules. If we bring all the ozone molecules in the atmosphere to the earth's surface and form a layer of pure ozone layer that covers the whole earth, the average thickness of the resulting layer is about 3 mm.

But it is this thin 3mm that plays a vital role in protecting life on Earth.

(ozone in the atmosphere) 2. The action of the ozone layer the structure of the ozone molecule makes it have a strong ability to absorb ultraviolet rays and can convert the energy of most ultraviolet photons into thermal energy:

Because of this characteristic, most of the harmful ultraviolet rays are stopped by the ozone layer, and the huge energy is converted into the basic heat energy heated above the stratosphere, so that the stratosphere can stably carry aircraft flight. it lays the foundation for the normal operation of surface organisms and weather systems.

At the same time, ultraviolet is also the main cause of the ozone layer; oxygen at the stratopause will form ozone under the action of short-wave ultraviolet (UVC):

(the process of stratospheric ozone production) in addition, some natural activities deplete ozone, such as volcanic activity. The Tonga volcano that erupted in January 2022 reduced the total stratospheric ozone over the southwest Pacific and Indian oceans by 5% in just one week; on September 16 this year, monitoring data from the European Space Agency showed that the area of the Antarctic ozone hole reached 26 million square kilometers, close to the largest in history.

In the long run, different natural activities and atmospheric chemistry keep the concentration of ozone in the atmosphere in a relatively stable range, but the situation seems to have changed in recent decades.

3. The crisis of the ozone layer in the early 20th century, with the help of the Carnot cycle principle, people found an effective refrigeration method, that is, by compressing and liquefying the gas, and then relying on the evaporation of the gas to absorb heat.

However, in the early refrigeration equipment, most of them used cheap and easily liquefied gases, such as sulfur dioxide (SO2) or ammonia (NH3). For example, SO2 can be liquefied at-10 ℃ or 2.5 atmospheric pressure, while NH3 can be liquefied at-33 ℃ or 9 atmospheric pressure.

Refrigeration equipment has brought comfort and convenience to people's life, but also planted the seeds of disaster.

SO2 and NH3 are both highly irritating and toxic gases. In 1929, a serious ammonia leak occurred in a large refrigerator used in a hospital in Ohio, killing more than 100 people.

The painful lesson forced people to actively look for alternatives to these toxic gases, and soon a very "excellent" substitute was found.

After the study of elements, American inventor Thomas Milic found a substance: difluorodichloromethane (CF2Cl2), which is a colorless, non-toxic, non-corrosive and irritating gas with a boiling point of-29.8℃, and the gas does not contain H element, can not burn, is considered to be an almost "perfect" refrigerant. In 1931, DuPont of the United States began large-scale industrial production of this compound, the trade name is "freon (Freon)" (in today's numbering system, the compound is R12). With its stable, safe and efficient advantages, freon has replaced almost all the previous refrigerants in a short period of more than ten years, and is popular in thousands of households. However, it is this kind of "almost perfect" that has left a huge scar on the earth.

In 1924, with the advent of the ozone spectrometer, human beings began to regularly observe the content of ozone in the atmosphere. During this period, under the leadership of British meteorologist Gordon Dobson, the United States, Egypt, India, the Soviet Union, New Zealand and Spitsbergen have successively established observation points of ozone concentration, which opened the prelude to the study of the ozone layer.

In 1957, shortly after World War II, a scientific team of the Royal Society built a Harreco station on the Brent Ice Shelf in Antarctica to make long-term observations of the atmosphere in the Antarctic.

In 1974, American scientists Mario Molina and Sherwood Roland proposed that the content of chlorofluorocarbons in the environment is steadily increasing, and that a large number of chlorine atoms produced by photolysis in the stratosphere can destroy the atmospheric ozone layer; the principle of this process is as follows:

Obviously, the chlorine free radical in this reaction is the catalyst, which can destroy the atmospheric ozone layer with high efficiency and act in the atmosphere for decades. The total reaction is roughly as follows:

(note: brominated hydrocarbons have a similar reaction, roughly as follows:

Although the catalytic process is basically the same as that of chlorine, the total reaction is:

It can be seen that although bromine and chlorine look alike, there are still some differences, and their catalytic reactions are essentially different.

(ozone destruction cycle 1) they mentioned that if HCFCs continued to be produced at an annual growth rate of 10 per cent at that time, the amount of ozone in the atmosphere would be reduced by 50.7 per cent in 20 years and 30per cent in 75 years.

The "difluorodichloromethane" mentioned above is a kind of HCFCs; it should be noted that the substances that destroy the ozone layer are not only HCFCs, but also halons such as difluorodichloromethane, trifluoromethane, and some other substances.

In the 1970s, the chlorofluorocarbon industry in the United States was worth more than $8 billion, directly or indirectly supplying 1.4 million jobs, so the government and chemical giants did not care about the research results. Plans to reduce or ban HCFCs have been greatly thwarted and cannot be implemented.

Ten years later, in 1985, scientists from the British Antarctic Survey made an amazing discovery.

They analyzed a large number of ozone observations at Harley Bay in Antarctica since 1956 and found that the amount of ozone in the atmosphere of Harley Bay in Antarctica decreased by more than 40 per cent in spring (September-November) between 1977 and 1984. This study was quickly confirmed by the scientific community. after the study, it was found that the ozone depletion in the upper atmosphere was more terrifying, and there was a huge "ozone hole" over the Antarctic continent.

This far more than the measured data studied a decade ago shocked the world and confirmed that chlorofluorocarbons have a great destructive effect on the ozone layer; for a time, the chemistry and kinetics of atmospheric ozone has become an upsurge of research. numerous theories and observations have proved this terrible situation, and there has been a sudden change in social attitudes towards substances such as chlorofluorocarbons.

4. Redemption-- "Women mend the Sky" Action as the international community realizes the imminent crisis of the ozone layer, this disaster has finally ushered in a turn for the better. On March 22, 1985, the international community signed the Vienna Convention for the Protection of the Ozone layer, announcing a magnificent plan to save the planet. Two years later, on September 16, 1987, at a conference in Montreal, the Montreal Protocol on substances that deplete the Ozone layer was unveiled, and a great "sky-mending action" was launched around the world.

These two historic documents vow to strengthen the control of ozone-depleting substances (ODS). The list of States parties brings together the world's major industrial countries, such as the United States, the Soviet Union, Germany and so on. China also acceded to the two conventions in 1989 and 1991 respectively, standing at the forefront of this defense war.

Driven by these agreements, not only industrialized countries have revamped their refrigeration systems, but also developing countries have adopted more environmentally friendly technologies. Harmful substances that have been widely used in refrigeration, fire fighting and cleaning are gradually withdrawn from the market.

Now, we are pleased to say that substances that once harmed the ozone layer in the past, such as refrigerants such as R12, fire extinguishing agents such as 1211 and 1301, and even carbon tetrachloride (CCl4), which were familiar in high school, are no longer manufactured and used, and they have been replaced by more environmentally friendly refrigerants and fire extinguishing agents, such as R134a (CH2FCF3), R32 (CH2F2), HFC-227ea (C3F7H) and Novec 1230 (C6F12O). These new materials basically do not cause damage to the ozone layer.

This history tells us that when people unite and work for a common goal, we have the ability to overcome environmental challenges, protect our planet, and create a more sustainable future. It also reminds us that each of us has a responsibility to remain committed to protecting our environment in order to ensure the sustainable development of our planet.

5. The impact of ozone hole on climate it is well known that the main function of the ozone layer is to block high-energy ultraviolet radiation from the sun and the universe, and to provide a good low-ultraviolet environment for life on Earth. Is the role of the ozone layer limited to this?

With the gradual development of atmospheric science, human beings gradually realize the deeper impact of the ozone layer, more accurately, the impact of stratospheric chemical composition on climate.

Despite the intensification of global warming, it is not actually heating up anywhere on the planet. As mentioned earlier, the ozone layer mainly exists in the stratosphere at the height of 20~50km. What is striking, however, is that the temperature here dropped slowly at a rate of about 0.6 ℃ per decade between 1960 and 2020.

The role of ozone in the atmosphere is to help maintain the temperature balance of the atmosphere, but if it is reduced, it will affect the way the atmosphere moves, especially in Antarctica, and may have an important impact on the Earth's climate and climate patterns.

When ultraviolet radiation from the sun enters the atmosphere, ozone converts these high-energy radiation into heat. This helps to protect the atmosphere from excessive ultraviolet radiation on the earth's surface, which is harmful to organisms and the environment. Therefore, if ozone is reduced, the stratosphere (part of the atmosphere) will not be able to absorb enough heat, resulting in a drop in atmospheric temperature. This is particularly true in the Antarctic region, that is, the Antarctic region of the Earth.

At the same time, there is a significant temperature difference between the South Pole and the equator. The equator is usually hotter, while the South Pole is colder. This leads to the flow of high-altitude air to Antarctica, which forms the westerly belt around the earth due to the earth's rotation and Coriolis force, that is, the area where the upper air flows west to east.

The westerly belt exists not only in the troposphere, but also in the stratosphere. Its existence greatly weakens the air flow between the Antarctic stratosphere and other regions; as ODS continues to enter Antarctica through various ways, the ozone consumed cannot be replenished, and an "ozone hole" is formed over Antarctica.

With the continuous expansion of the ozone hole over Antarctica, the temperature of the stratosphere in this region gradually decreases, increasing the temperature difference between Antarctica and the equator, and strengthening the circum-Antarctic westerly belt and polar vortex. This change will affect the troposphere in about half a month through extremely complex meteorological principles, strengthening the tropospheric circum-Antarctic westerly belt; so what impact will this have?

The energy of the wind will affect the flow of the sea. The strong westerly belt will accelerate the flow speed of the Antarctic circumpolar current, and at the same time, through the stronger Ekmen transport, a large amount of polar surface water will be transported northward, causing the warm water in the lower polar layer to move upward, warming the surface layer of the Southern Ocean and reducing Antarctic sea ice.

At the same time, we need to know that the energy of the stratospheric unstoppable ultraviolet radiation does not disappear out of thin air. It rushes to the surface, heats the troposphere, and further affects our weather system and atmospheric flow.

However, the influence of ozone hole is only one of many factors affecting atmospheric system and ocean system, which is limited in theory and difficult to prove. For example, sea ice in Antarctica grew from about 2.5 million square kilometers to about 3.6 million square kilometers between 2010 and 2015, and plummeted to 1.92 million square kilometers last year.

At present, we are unable to accurately simulate the weather system, so it is impossible to confirm the impact of the hole in the ozone layer, but in this war, we finally see the dawn of victory.

According to the research of American meteorologist Antara Banerjee and others, it can be confirmed that with the effective implementation of the above two conventions, the changes in atmospheric circulation caused by the ozone hole in Antarctica have basically stopped, and the atmospheric changes caused by ozone depletion will also be gradually restored.

Unity continues the spark of civilization. It can be said that the solution to the problem of the ozone layer is not the work of the gods and saviors, but that each of us has become the "Nu WA" of mending the sky, atoning for previous mistakes and changing in order to live in harmony with nature. It is hoped that mankind can overcome danger, get along well with nature, unite as one and have a sustainable civilization in the distant future.

This article is from the official account of Wechat: stone popular Science Studio (ID:Dr__Stone), author: Tianyin

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