Hello, friends! In October 1982, at a research station in Antarctica amidst snowstorms, scientist Joseph Farman was taking some measurements. He was measuring the amount of ozone in the Earth's atmosphere using a machine. Suddenly, the machine gives a very strange reading. According to the machine, the amount of ozone in the atmosphere has decreased by 40% compared to normal. Joseph was not surprised to see this. He looked at the strange number and thought, how could ozone levels drop 40%? There must be something wrong with the machine. Perhaps, the machine was not working properly. It was considerably old, after all. He thought that had the ozone level really fallen so low, then it would've been detected by the thousands of orbiting NASA satellites. So he packed his stuff and went home. The next year, in October 1983, he returned. This time he brought a new machine with him. And took the measurements again. According to the readings this time, the ozone level had decreased even more compared to last year. He was sure that something was wrong. Such unbelievable reading was not possible. But once again, he thought that if there was a problem, then agencies like NASA would have found it. Yet again, he packed his stuff and went home. Another year later, in October 1984, when they returned to do his work, he decided to take the reading from some other research station. About 1,000 miles away from his original research station, he set up the machine again for reading and took the measurements. He found that the ozone level had deteriorated even more. Here he realised that it was an emergency situation. He went to NASA with the evidence and soon the world got to know about the ozone hole over Antarctica. Surprisingly, this ozone hole was growing rapidly each year. NASA scientists had overlooked it. When they went back to look at their satellite data they saw such photos. In 1979 everything was completely normal. In 1980 and 1981, things started turning blue. In 1982, a proper hole was visible. By 1983, this hole got bigger. And the next year, 1984, this hole had become this big. The world went into a frenzy with this news. If the ozone layer kept depleting from the atmosphere, it would be a terrible event. A warning bell for all the plants, animals and humans on Earth. If ozone is depleted, life on Earth will be over. And the rate at which this hole was getting bigger, it was predicted that by 2050, the ozone layer will be completely depleted. "Every October, a hole appears in
the ozone layer over the South Pole." "The hole in the ozone shield is
the size of the continental United States." "The protective ozone layer is
being threatened as never before. We're all at risk." "Ozone depletion is not a natural thing. It stems from human emissions of chemicals called Chlorofluorocarbons, or CFCs." Friends, before we move on with the story let's understand the ozone layer first. As you have studied in school, Ozone is a gas. Its chemical formula is O3. While the chemical formula of Oxygen is O2. The ozone molecule is made up of 3 oxygen atoms. Friends, about 600 million years ago the ozone layer was formed around Earth. This is a zone in the atmosphere of Earth which is about 15-35 km above the surface of Earth. 90% of the ozone on Earth is found in this area. Ozone concentration is found to be
highest at 32km above the surface which is at 0.0015%. It's not a big number. This gas is found in a very small amount in the atmosphere. But even such a small amount is important for the Earth. Ozone is made from oxygen when the sun's ultraviolet radiation hits the oxygen molecules. A very simple chemical reaction takes place. Because of ultraviolet radiation, the oxygen molecules split into oxygen atoms. And when these separated atoms mix with the oxygen molecules, ozone is formed. O2 + O = O3. Now, there is a constant cycle that keeps on repeating. Often, the ozone molecule collides with an oxygen atom and oxygen is formed again. A cycle of these two reactions continues and this entire cycle is called the Chapman cycle. This was named after scientist Sydney Chapman who explained this chemical reaction for the first time in May 1929. This reaction is called Photodissociation or Photolysis. Photo means light and dissociation means splitting up. The atoms split up because of light. The Ozone layer is mainly known for protecting us from harmful sun rays or UV radiation. UV rays can cause sunburns, weakening of our immune system, cataracts and skin and eye cancer. Now you might be thinking that if ozone's job is to protect us from UV rays, then why do we apply sunscreen to protect ourselves from UV rays? The reason behind this is very interesting. Actually, almost all wavelengths of radiation are emitted by the sun. Almost all types of rays in the electromagnetic spectrum, are emitted from the sun. Be it visible light, which is between 380-700 nm, or UV rays, gamma rays or X-rays. These 3 rays fall in the 'harmful' category because they are ionizing and their long-term exposure is very harmful to humans. They can tear our bodies apart to go inside and change our DNA. Now, in the ultraviolet range there are 3 categories of UV rays. UV-A is a wavelength of 315-400 nm. UV-B is a wavelength of 280-315 nm. And UV-C is a wavelength of 100-280 nm. UV-C has the smallest wavelength and is the most dangerous. Followed by UV-B and then UV-A. Our ozone layer stops X-rays, gamma rays, and UV-C rays from reaching the Earth. UV-B radiation is only partially absorbed by the ozone layer. And UV-A is not absorbed at all. And it passes through the ozone layer. That's why sunscreens protect us from UV-A and the remaining UV-B radiation. Most of the sunscreens protect you from UV-B radiation only. That's why you are always told to buy broad-spectrum sunscreen. A sunscreen that protects you from both UV-A and UV-B radiation. Here, for the collection and analysis of UV radiation data, Data Science has played a major role. Using it, scientists have been able to find out the harmful effects of various wavelengths on our skin. This data analysis was used by various companies to formulate sunscreens to figure out which combination of ingredients will provide the best protection against ultraviolet radiation. Studying, managing, and analyzing big data sets is an important part of data science. And because it can be used in almost every field, data science has become one of the most lucrative careers today. If you are interested in upskilling yourself in this field, then the sponsor of today's video, Scaler.com will be very useful for you. Scaler is an online tech learning platform that offers programs for software development, data science, and machine learning. Subject matter experts from top tech companies guide and mentor learners. They believe that you should become 1% better every day. Learners are provided with 3 hours of daily learning and access to more than 80 real-world case studies. Here you get one-on-one mentorship and placement assistance too. They claim that the learners who worked hard and completed their program got an average salary hike of 126% on average. And 93.5% of the learners were placed in top tech companies like Google, Facebook, Flipkart, Myantra, Amazon, Apple, and Zomato. So if you are interested in growing your career, you can check out Scaler. The website link is in the description below. You can sign up for a free live class and decide for yourself how useful it is. You also get an EMI option. You can go check it out. Now let's get back to our topic. When we talk about the depletion of the ozone layer, you can understand how threatening it is, because then UV-C radiation could reach the Earth. Along with other harmful rays. This is the reason, friends, that before the creation of the ozone layer on Earth, 600 million years ago, life on Earth was so deep in the ocean so that harmful radiation could not reach it. But photosynthesis was still possible. When life came out of the water and landed on the ground due to evolution, to some extent, the ozone level is also credited for this. Only after the development of the ozone layer, complex multicellular organisms were able to live in the sea at shallow depths. They got more exposure to sunlight and eventually, they were able to live on land. I have talked about this in detail in the evolution video. Before the formation of the ozone layer, there was nothing to protect the earth from harmful radiation. But only 50-60 million years after its formation, we saw diversification in life. Though this happened millions of years ago, humans only came to know about these only 200 years ago. In March 1839, a scientist at the University of Basel, Switzerland, Christian Schönbein, was experimenting with the electrolysis of water. By using electricity, he was separating water into oxygen and hydrogen. While doing these experiments, he noticed a strange smell. This smell was emitted by a gas. And when he isolated this gas, he named it Ozone. The word Ozone actually comes from the Greek word Ozein, which means to smell. Since there was a smell, the gas was named after the act of smelling. 26 years later, in 1865, it was discovered that the ozone molecule is made up of 3 oxygen atoms. And later on, scientists also discovered that harmful radiations get blocked out by ozone. This gas turns into a dark blue liquid at a temperature of -112° Celsius. And at -193° Celsius, it becomes solid. A deep purple-coloured solid. It was also found that exposure to this gas is actually toxic for humans. While in the atmosphere, this gas is definitely protecting us but in close proximity to humans, it is harmful to us. If we talk about the smell, it is similar to the smell of sparks from electrical equipment. Or the smell of the soil during thunderstorms. Some people find this smell sweet and fresh while others think it is metallic and like bleach. In 1921, a British geophysicist, G.M.B. Dobson made a machine which can measure the concentration of ozone in the atmosphere. This machine is called Dobson Spectrophotometer. Even now, this is the standard device with which we measure ozone in the atmosphere while remaining on the ground. In fact, the concentration of ozone is measured in Dobson units. So, even the units are named after him. The normal thickness of the ozone layer is 3-5 mm which is 300-500 Dobson units. After 8 years of making Dobson's machine, Sidney Chapman made equations of ozone formation and introduced the Chapman cycle to the world. The ozone present at the ground level, as I told you, is harmful to humans. So it is called Bad Ozone. When Scientist Schonbein was working with ozone, he suffered chest pains and difficulty breathing. He also observed that in an ozonized environment, the smaller animals would d!e. Today, bad ozone is increasing due to the use of fossil fuels. Specifically, the nitrogen oxides, NOXs, like nitrogen dioxide, when they are released due to burning coal or from the exhaust of a car, ozone is formed at the surface level. Due to the heat and UV rays the nitrogen dioxide is split into nitrogen oxide and a single oxygen atom. And this oxygen atom reacts with the oxygen molecule to form ozone. Besides nitrogen oxides, VOCs are also responsible. Like benzene, which is produced from gasoline combustion. Sometimes it evaporates from paints that are applied on the walls. Or it is found in nail polish removers. It is worth noting that the level of bad ozone forming often depends on the weather conditions. In the summer months, more of it is formed. Due to more UV radiation and more heat. On the other hand, when it rains and there is high humidity, fewer ozone molecules are formed. This is why ozone is also considered an air pollutant. See this article from 2023. "Ozone emerges as lead air pollutant in Delhi." We often focus more on air pollutants like PM2.5, carbon monoxide, and nitrogen oxide and ignore ozone. Some of you may think that is this not a good thing? Since a large amount of ozone is being produced on the ground while there is an ozone hole above us. The ozone at the surface level can simply go up to close the ozone hole. This seems beneficial. But unfortunately, this does not happen. The first reason is that this ozone does not ascend upwards. And the second reason is that the concentration which is harmful to us on the surface, is still a very low concentration compared to the concentration we need in the atmosphere to make the ozone layer. And as you saw from the different chemical reactions, ozone is a very reactive gas. So we cannot transport it higher into the atmosphere easily. Now the question arises if so much ozone is being formed due to human activities, how did the ozone hole form? It began in the 1950s-60s. There were many research stations in Antarctica which were set up to study space, Earth and weather. Some of these research stations were actually monitoring the ozone layer. Specifically, there was an American station in Antarctica from 1961 where a Dobson spectrophotometer was installed. In August 1964, for the first time, satellites were used to measure ozone concentration. These were weather satellites from NASA's Nimbus program. In the 1970s, NASA was worried that the spacecraft that they were sending to the moon might disturb the atmosphere. They feared that the spacecraft might hurt the ozone layer. Fortunately, the spacecraft didn't have any negative effects. But the negative effects were caused by some other small daily life things. A chemical that was in your hair spray bottle, in the can of shaving cream, and was used as a solvent in the fridge. We call this chemical category as Chlorofluorocarbons, i.e. CFCs. In June 1974, a controversial scientific paper was published by these three scientists which won the Nobel Prize. In this scientific paper, they showed how the ozone in the atmosphere is getting depleted due to CFCs. These scientists warned that CFCs have a lifespan of 40-150 years and they have the potential to completely deplete the ozone layer. These scientists were mocked after the publication of this paper. Some people didn't believe it at all. They said that it was nonsense. By that point in time, CFCs had become very common chemicals. They were being used in a lot of manufacturing applications. The advantage of CFCs was that they were very stable on the ground. But the problem was that when they would go into the atmosphere and collide with the radiation of the sun, they would release chlorine into our atmosphere. And after the release of chlorine gas, a dangerous reaction would take place. Look at this chemical reaction. This chlorine gas reacted with the ozone molecules and formed oxygen and chlorine monoxide. And as I told you in Chapman's cycle, a cyclic reaction was already taking place. So, the individual atoms of oxygen were already present in the atmosphere. And this chlorine monoxide would react with the oxygen atom and would form oxygen and chlorine. Do you understand the effect of these two reactions? Chlorine reacts with ozone and after the second reaction, chlorine is released again along with oxygen. That means the chlorine that is released again can react with the remaining ozone again which will deplete the ozone and produce more chlorine. This became a dangerous loop. One chlorine atom could break apart thousands of ozone molecules. Later, some scientists experimented to find out the truth of this scientific paper. And they found it to be true. Each chlorine atom present in these CFCs was causing a devastating effect on the ozone layer. But scientists still estimated that if things continued like this, then due to CFCs, 2-4% of the ozone layer would be destroyed by the year 2099. This was the theoretical prediction of the scientists. So, people didn't worry much. Then, we come to the story of Joseph Farman, which I told you at the beginning of the video. Joseph Farman, stationed in a research station in Antarctica, went there every year to measure the ozone level in the atmosphere. Suddenly, in 1982, his reading showed that 1/3rd of the ozone layer was already depleted over Antarctica. This reading was unbelievable because scientists had assumed that only 2-3% of the ozone layer will be depleted. That's why he thought that his machine must have broken down. So, the next year, they brought a new machine. And it showed the same reading again. Then he assumed that the problem must be with the location. So, he went to another location. And again, he saw the same thing. And when he went ahead and told NASA, NASA's scientists measured it themselves, and these horrific images were released. Here, we could see that each year, the ozone hole was widening so rapidly. All the theoretical predictions by the scientists, were drastically wrong. The situation was actually horrendously dangerous. In August 1985, the first map was shown to the world of the ozone hole, and how the ozone hole looked over Antarctica. The measurements at the bottom of this map are in Dobson units (DU). As I told you, 300 to 500 units was the normal measurement of the thickness of the ozone layer. But in the middle of the ozone hole you can see that these measurements had fallen below 200 DU. In some places, it was almost 150 DU. "Every October a hole appears in
the ozone layer over the South Pole. What worries scientists most is
they're still not exactly sure what causes the hole." Now that you have understood the scientific background, you can understand that this ozone hole is not actually a hole. It is a metaphorical way of saying that the ozone layer has thinned a lot. Over that area. The phenomenon which we call the 'ozone hole', is that part of the ozone layer whose thickness has decreased by one-third. In 1977, its readings measured 250 DU. In reading from 1984, it was measured to be 160 DU. It was obvious that immediate action was needed. But the scientists were still stumped by a question. Why is the ozone hole forming only over Antarctica? Many reasons were speculated. First, the air that rises converges towards the North and South Poles. So, the depletion of the ozone layer was not only seen over Antarctica but was also seen over the Arctic. But in Antarctica, it was more prominent. The reason behind this was said to be the polar stratospheric clouds. These are a type of clouds that are seen over Antarctica. The droplets of these clouds contain a mixture of nitric and sulfuric acids. And chemicals like chlorine and bromine react on the surface of these droplets to break down the ozone. These clouds form only at a temperature of -78° Celsius. Because of this, this reaction progresses. But such cold conditions are not so common in the Arctic. They are mostly found over Antarctica. That's why this ozone layer thinning was most visible here. Usually, in the stratosphere of our atmosphere, the air is not very cold. At the starting point, the average temperature is -51° Celsius. And at the top, the average temperature is -15° Celsius. After this, the temperature increases only when the height increases. This is why Antarctica was the most vulnerable to this threat. But the good news in this story is that politicians took immediate action. After this finding in 1985, the next year, in 1986, the United Nations began negotiations on it. They started drafting a treaty to ban CFCs all over the world. In 1987, a Montreal Protocol was formed, which came into force in 1989. The amazing thing was that this became the first United Nations treaty in global history, which was signed by every country. All 198 member countries of the United Nations ratified this treaty. Because of this, CFCs were replaced by HFCs, Hydrofluorocarbons, which had no negative effect on the ozone layer. In the 1990s, these nations started taking action and the use of CFCs declined. Still, in 2000, the largest ozone hole was discovered, which was almost spread over 30 million km². This is because there's a delay between
taking action and seeing its impact. But positive results were seen soon. The global CFC consumption was 800,000 metric tons in the 1980s. By 2014, it fell to only 156 metric tons. 99% of the CFCs were eliminated collectively by all the countries. This is, perhaps, the biggest achievement in the history of humanity. Within 5-10 years, the problem was identified and all the countries in the world started acting on the solution. And today we can see the result. The ozone hole is getting smaller. According to the United Nations report released in January 2023, over the next 40 years, things will return to normal and the ozone hole will be completely eliminated. They have projected that by the year 2040, the ozone layer will return to the level in 1980. By the year 2045, the ozone hole above the Arctic will completely disappear. That means our ozone layer will recover completely. And above Antarctica, our ozone layer will recover completely by the year 2066. Two years ago, another study found that by banning CFCs, we have also controlled some significant effects of climate change. If CFCs were still used, then the global temperature would have increased by an additional 2.5° Celsius by 1999. In 2016, Hydrofluorocarbons, or HFCs, were added to the list of controlled substances. Over the next 30 years, governments will try to phase out HFCs too. This is because HFCs are greenhouse gases which are thousand times more effective than carbon dioxide in trapping heat. So even though HFCs have no negative impact on the ozone hole, their negative impact is seen in climate change. From this story, we learn a very important lesson. If governments and people all over the world fight about the world's problems unitedly, then the solution can be found very soon. The next big problem that the world is facing today is climate change. And once again, all the people and governments need to take united action to deal with this problem. What's your opinion? Write in the comments below. If you liked this video, you can click here to watch the video on Cloud Seeding, in which I have explained the technology of artificial rain and cloud seeding. Thank you very much!
