Does the ozone layer still have a hole? Yes, the ozone layer does still have a hole, although it is slowly repairing itself.
The ozone layer is not very thick, but it is vital to our survival on this planet. We talk about a hole in the ozone layer, but it is not an impenetrable forcefield with a big hole in it. It is a gas that spreads around the planet and the hole is a place where it has become very thin. Ozone is a gas that is made of 3 oxygen atoms joined together. Ozone concentrates in the lower half of the stratosphere, which is the second layer of the atmosphere above Earth. The first one is the troposphere and that goes from the ground up to about 12 km. Then the stratosphere goes from there up to about 50 km. The mesosphere goes from 50 km up to 80 km. That’s followed by the thermosphere, which goes up to 700 km. And the last layer is the exosphere, which goes from 700 km out to 10,000 km. The thermosphere is very thin, and the exosphere is the layer where atoms and molecules are lost to space.
Ozone is spread out throughout the stratosphere, but it is not very concentrated. There are roughly 10 ozone molecules for every 10 million molecules of air, which is not a lot. Despite this, ozone is vital. The 3 molecules of oxygen that make up ozone are very good at absorbing energy that is in the ultraviolet band. The sun emits a lot of energy as electromagnetic radiation. The radiation has different wavelengths, and most of them we can’t see. The only ones we can see are the wavelengths in the visible light spectrum. Radiation with more energy has shorter wavelengths, and lower energy has longer wavelengths. The energy band just above the visible spectrum is called ultraviolet radiation and that is very dangerous for us and for almost every life form on Earth. We have been able to evolve here on Earth because the ozone in the atmosphere does a very good job of absorbing the UV light and stopping it from reaching us.
When ultraviolet light hits the stratosphere, it collides with an ozone molecule (which is three oxygen atoms). The extra energy makes the ozone molecule break up into a molecule of oxygen, which has two oxygen atoms, and an individual oxygen atom. When they break up, they release the energy as heat into the atmosphere, which means, unlike the troposphere, the temperature increases as you get higher up. The bottom of the stratosphere is -51℃ and the top is only -15℃. When the oxygen atoms break up, the individual atom is very unstable and desperately needs to reconnect with another oxygen atom. That means the three oxygen atoms regroup, and another ozone molecule is created. Through this process, ozone is created, absorbs UV light and breaks up, releases the energy as heat, and the oxygen molecules rejoin to make ozone again. It is an ongoing process that absorbs about 99% of all the UV light that hits our planet.
If we didn’t have an ozone layer, all of that high energy radiation would make it down to the surface, and everything would die. Plants wouldn’t be able to use it to photosynthesize because the energy level is too high, and it would kill them. Even if we lived in caves and managed to avoid getting skin cancer, with no plants, there would be no animals, and we would have no food. We would all die.
So, what is the hole in the ozone layer? The amount of ozone in the stratosphere is measured using Dobson Units (DU). They are named after the British meteorologist G. M. B. Dobson. The average level of ozone in the atmosphere is 300 DU. The ozone hole is anywhere that has less than 220 DU. That is why it is not technically a hole, rather a thin bit. The thinning of the ozone layer has been caused by several chemicals that we have released into the atmosphere. One of the most famous of them are called chlorofluorocarbons (CFCs). They were used in refrigeration, spray cans, plastic products, and a host of other places. CFCs are very light, and they can float up into the stratosphere, which is where they do their damage. UV radiation breaks apart the oxygen atoms in ozone, and it also breaks the CFCs into chlorine. When the chlorine finds the individual oxygen atom, it makes chlorine monoxide. This chlorine monoxide can react with other individual oxygen atoms and make a chain of chlorine monoxide, destroying hundreds of thousands of oxygen atoms. Without these individual oxygen atoms, the ozone can’t reform.
By the time scientists realized what was happening, there was a huge thin patch in the ozone layer over Antarctica. It formed there because the weather conditions mean that a lot of the CFCs were naturally transported there and the temperature means stratospheric clouds form, which hold the CFCs in place, allowing them to do even more damage. Luckily, once the problem was observed, the solution was fairly simple: CFCs were banned in a relatively (for us) short time frame and now there are only a few countries that still use them. This has cut down on the depletion, and the ozone layer is gradually returning. It will take until 2066 before it is back to the level before we started using CFCs, but we are going in the right direction. That gives me some hope because we can act to fix the planet when we need to. The problem is, though, that fixing the ozone layer was fairly straightforward because only one gas had to be banned, and there were alternatives. To fix global warming will take a lot more action. Also, the oil industry had no vested interest in CFCs, so they weren’t actively trying to spread disinformation as they are doing with climate change. And this is what I learned today.
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Sources
https://education.nationalgeographic.org/resource/ozone-layer
https://earthobservatory.nasa.gov/images/153523/ozone-hole-continues-healing-in-2024
https://www.weforum.org/stories/2024/11/ozone-layer-hole-update-nasa
https://www.epa.gov/ozone-layer-protection/basic-ozone-layer-science
https://www.epa.gov/ozone-pollution-and-your-patients-health/what-ozone
https://www.noaa.gov/jetstream/atmosphere/layers-of-atmosphere
https://ozone.unep.org/ozone-and-you
https://en.wikipedia.org/wiki/Ozone_layer
https://science.howstuffworks.com/science-vs-myth/what-if/what-if-ozone-layer-disappeared.htm
Photo by Lukas: https://www.pexels.com/photo/sunlight-with-white-clouds-296234/