Lesson video

Hello, I'm Mrs. Adcock, and welcome to today's lesson on the Ozone Layer: A Story of Global Success.

Today we are going to be looking at the ozone layer and how the work of scientists led to a global effort to reduce the hole in the ozone layer.

Today's lesson outcome is, I can describe why the ozone layer was nearly destroyed, but through a global community and international resolution it was saved.

Some of the keywords that we will come across in today's lesson include, ozone, ozone layer, ultraviolet radiation, which is shortened to UV radiation, chlorofluorocarbons, and analytical scientists.

Here you can see those keywords written in sentences.

You might like to pause the video here and read through those sentences, or you might like to pause the video and make a note of those keywords so that you can refer back to them later on in the lesson.

Today's lesson on Ozone Layer: A Story of Global Success is split into three parts.

The first part of the lesson is on the importance of the ozone layer, the second part of the lesson is on chlorofluorocarbons, which are shortened to CFCs, and the final part of the lesson is on reforming the ozone layer.

So let's get started on the importance of the ozone layer.

The ozone layer refers to a high concentration of ozone molecules, which are found in the stratosphere.

And ozone, as you can see there, has the molecular formula O3 and it's three oxygen atoms joined together.

We can see a diagram there of the Earth, and those rings represent the atmosphere surrounding Earth.

And the atmosphere is split into subsections called the troposphere, the stratosphere, the mesosphere, the thermosphere, and the exosphere.

And that high concentration of ozone that we refer to as the ozone layer is found within the stratosphere, and it's about 15 to 30 kilometres away from the surface of the Earth.

Time for a check for understanding.

What is the molecular formula of ozone? Is it A, O, B, O2, or C, O3? Well done if you chose C.

O3 is the molecular formula of ozone.

O is just an oxygen atom by itself and O2 would be a molecule of oxygen.

Another question for you to have a go at.

Where in the atmosphere is the ozone layer? Is it A, in the troposphere, B, in the stratosphere, or C, in the mesosphere? Well done if you chose B.

The ozone layer is found in the atmosphere in the area known as the stratosphere.

Now we're going to have a look at why the ozone layer is so important.

The ozone layer protects life on Earth from harmful ultraviolet radiation from the Sun.

And in the diagram there we can see the Sun at the top and Earth at the bottom, and in the atmosphere is that ozone layer.

And the ozone layer is absorbing some of that ultraviolet radiation from the Sun and stopping it from reaching the Earth's surface.

So, how much ultraviolet radiation does the ozone layer absorb? Well, it only absorbs about 5% of a type of ultraviolet radiation known as UV-a, and we can see that on the diagram shown in the yellow.

So most of the UV-a from the Sun reaches the Earth's surface, with only about 5% being absorbed by the ozone layer.

However, the ozone layer does absorb about 95% of the UV-b that was emitted from the Sun, so only a small percentage of UV-b reaches the Earth's surface because about 95% of it was absorbed by the ozone layer.

And that's shown there in the diagram in orange.

And the ozone layer absorbs 100% of UV-c radiation that was emitted from the Sun, so that prevents any of that UV-c from reaching the Earth's surface.

UV-a, UV-b, and UV-c differ because they have different wavelengths.

UV-a has the longest wavelength and UV-c has the shortest wavelength.

Humans wear sunglasses and sunscreen to provide protection from UV radiation that has reached Earth's surface from the Sun.

And depending on the brand of sunscreen that you purchase, it will provide protection generally against UV-a and UV-b radiation.

Without the ozone layer, high levels of ultraviolet radiation, now UV-a, UV-b, and UV-c, would get through the atmosphere and the impacts of this is that they would cause sunburn, skin cancer, and cataracts.

Cataracts are a clouding of the lens of the eye, and this will impact your vision, such as it might make it cloudy or blurry.

And there's an image there of a dog suffering with cataracts, and you can see the cloudiness of the lens.

Time for a check in understanding.

The ozone layer absorbs which type of radiation? Is it A, ultraviolet radiation, B, infrared radiation, or C, microwave radiation? Well done if you chose A.

The ozone layer absorbs ultraviolet or UV radiation.

We're gonna have a go at another question.

Which two types of ultraviolet radiation does ozone absorb a high percentage of, preventing it from reaching Earth's surface? Is it A, UV-a, B, UV-b, or C, UV-c? And remember you're choosing two types of UV radiation that ozone absorbs a high percentage of.

The correct answers are B, UV-b, and C, UV-c.

Remember, ozone absorbs about 95% of UV-b and 100% of UV-c radiation, preventing it from reaching Earth's surface.

Well done if you identified both of those.

Time for our first practise task of today's lesson.

The first question is, what is the role of the ozone layer? And then for question two, what would happen if there was no ozone layer? If you pause the video here, have a go at those questions and come back when you're ready to go over the answers.

Question one, what is the role of the ozone layer? The ozone layer absorbs about 95% of UV-b and 100% of UV-c, preventing this harmful radiation from reaching Earth's surface.

So well done if you wrote a similar answer to that, explaining the role of the ozone layer.

Question two, what would happen if there was no ozone layer? If there was no ozone layer, then harmful UV-b and UV-c radiation would reach Earth's surface causing sunburn, skin cancer, and cataracts.

Well done if you were able to identify some of the impacts to humans and other life on Earth if there was no ozone layer.

Time for us to move on to the second part of our lesson on chlorofluorocarbons, which fortunately we can shorten that name and call them CFCs.

So chlorofluorocarbons, or CFCs, are haloalkanes.

Now, an alkane is a molecule that has a carbon backbone and it has hydrogens bonded to it.

And in a haloalkane we've replaced some of those hydrogen atoms with halogens.

And just remember that halogens are elements from group seven.

So chlorofluorocarbons are haloalkanes where all of the hydrogen atoms have been replaced with chlorine and/or fluorine atoms. And we've got an example of some chlorofluorocarbon molecules shown below.

So you can see they've both got carbon atoms, and bonded to those carbon atoms instead of it being hydrogens, they've all been replaced with either chlorine or fluorine atoms. So the chloro stands for chlorine, fluoro is the fluorine atoms, and then we've got carbon as well.

Which of these molecules is a chlorofluorocarbon? So remember you're looking for chlorine, fluorine, and carbon only in those molecules.

Well done if you chose B.

A and C are not chlorofluorocarbons because they've still got some hydrogen atoms bonded to the carbon.

B is a chlorofluorocarbon because we've just got chlorine and fluorine and carbon in that molecule.

Well done if you chose B.

Chlorofluorocarbons were once used in many products such as fridges, aerosol cans, and air conditioning.

CFCs are non-toxic, non-flammable, volatile, and stable, and this is why they've been particularly useful in those products.

However, because they are volatile and stable, and just a reminder that volatile means they will easily evaporate, so they're often found in the gaseous state, then what happens is they can enter the lower atmosphere and they do not get broken down because they are stable, but they remain in the atmosphere, and over time they can travel up to the ozone layer.

CFCs then react with the ozone in the ozone layer, breaking it down into oxygen molecules, which have the formula O2.

So we've broken down that O3, which was ozone, into oxygen molecules, which are O2.

And one chlorine atom from a CFC molecule can destroy about 10,000 ozone molecules.

The breakdown of ozone by chlorofluorocarbon molecules has led over time to what scientists describe as a hole in the ozone layer.

So it's an area of the ozone layer where the concentration of ozone has really decreased and is very thin, so it's described as a hole.

We can see here in some images from NASA that they've mapped the ozone levels.

And here we can see in September, 1979 that there doesn't appear to be any holes in the ozone layer.

However, in this ozone map from September, 1989, we can see that there is some dark blue and that dark blue area represents a hole or a thinning in the ozone layer.

The hole in the ozone layer was first discovered by scientists in 1985.

Time for another question.

Where were chlorofluorocarbons once used? Is it A, fridges, B, aerosol cans, C, paint, or D, air conditioning? Now choose any answers that you think are correct.

The correct answers are fridges, aerosol cans, and air conditioning.

So well done if you chose options A, B, and D, they are all places where CFCs were once used.

What impact does the use of CFCs have on the levels of ozone in the atmosphere? So, do CFCs cause an increase in ozone levels? Do CFCs have no impact on ozone levels? Or do CFCs lead to a decrease in ozone levels? The correct answer is C, CFCs lead to a decrease in ozone levels.

So well done if you chose option C.

Time for our second practise task of today's lesson.

You've got three questions here.

Question one, what are chlorofluorocarbons? So you just need to describe what these are and make sure you've mentioned each part of the word, so chloro and fluoro and the carbon part.

Question two, draw one example of a CFC molecule containing only one carbon atom.

Now, there's lots of different molecules you could draw here, you just need to draw one example.

Question three, describe the impact of using CFC molecules on the ozone layer.

If you pause the video here, have a go at answering those three questions and then come back when you're ready to go over the answers.

What are chlorofluorocarbons? Chlorofluorocarbons are molecules made of chlorine, fluorine, and carbon atoms only.

Question two, draw a structure of a CFC molecule containing only one carbon atom.

Some possible answers include, one carbon atom with three chlorines and one fluorine.

Here we've got the one carbon atom still, but we've got two chlorines and two fluorines.

And finally we've got one carbon atom, but this time we've got three fluorines and only one chlorine.

Well done if you've got those two questions correct.

Question three, describe the impact of using CFC molecules on the ozone layer.

Chlorofluorocarbons react with ozone in the ozone layer causing it to break down into oxygen molecules.

And each CFC molecule can break down thousands of ozone molecules.

Time for us to move on to the final part of our lesson, which is on reforming the ozone layer.

Scientific evidence gathered by analytical scientists showed the impact of CFC use on the ozone layer and led to the ban of CFCs.

Now, this is brilliant.

The scientists discovered that there was a thinning of the ozone and then they communicated this idea and this led to international treaty.

And in 1987, the international treaty, called the Montreal Protocol, called for the phasing out of CFCs apart from in a few permitted uses such as in medical inhalers.

And since then, scientists have developed an alternative inhaler which uses hydrofluoroalkanes, so HFAs, instead of CFCs.

And there's an image there of a HFA inhaler, which some of you may recognise.

This is great that internationally there was a ban on the use of CFCs to try and stop the damage to the ozone.

What led to an international ban on the use of CFCs? Was it that governments were concerned about economic growth? Or B, that industries wanted cheaper alternatives to CFCs? Or was it C, scientific evidence of the impact on the ozone layer? The correct answer is C.

It was scientific evidence that led to an international ban on the use of CFCs to try and limit the impact on the ozone layer.

The hole on the ozone layer has stopped increasing because of this ban on CFC use and is slowly reforming.

And here we've got two images showing the ozone map, and we've got one from September, 1989, and we can see that dark blue area showing a huge hole in the ozone layer.

And then there's another ozone map from December, 2023, and we can see there is a much smaller hole in the ozone layer.

And it is thought that that ozone hole will be fully healed by somewhere between 2040 and 2070.

Hydrochlorofluorocarbons, so they are shortened to HCFCs, and hydrofluorocarbons, shortened to HFCs, are sometimes used as replacements for CFCs.

And if you just have a look at their names, then you can see the difference here is that these have got some hydrogen in them as well.

So there's less chlorine and less fluorine atoms because we've now replaced some of those with hydrogen atoms. These have a smaller impact on ozone levels, they are less damaging to the ozone layer, however, they are greenhouse gases, so they can impact global warming.

We've got an example here of a HCFC molecule and you can see it's got hydrogen, chlorine, fluorine, and carbon atoms in the molecule, and a HFC molecule, which has got hydrogen, fluorine, and carbon atoms. HCFCs and HFC molecules do not persist in the atmosphere for as long as CFCs.

And scientists continue still to try and find alternatives to CFCs.

And some of these you will recognise.

Many aerosols now have pump systems or they use nitrogen as the propellant so that we no longer use CFCs in aerosol cans.

And as a coolant in fridges, instead of using CFCs, many fridges now use ammonia, which has the molecular formula NH3, as the cooling gas.

You can see in that image we've got a model of ammonia, which is one nitrogen and three hydrogen atoms. Time for a question to check for understanding.

Which of these molecules has a less damaging effect on the ozone layer than CFCs? So we are looking for an alternative to CFCs so that it has a less damaging effect on the ozone layer.

So look closely at the atoms in those molecules and see if you can identify which ones have a less damaging effect on the ozone layer.

Well done if you chose A.

A is a hydrochlorofluorocarbon because it has hydrogen, chlorine, fluorine, and carbon atoms. And you should have also chose B.

B is a hydrofluorocarbon.

It's got hydrogen, fluorine, and carbon atoms. And C is a CFC, so that would be an incorrect answer.

It's got chlorine, fluorine, and carbon atoms only.

For our final practise task of today's lesson, there's two questions to answer.

Question one, describe how scientific evidence has led to ozone in the ozone layer reforming.

So think about the work that those scientists did and how their communication has led to ozone in the ozone layer reforming.

And question two, can you state two alternatives to CFCs? If you pause the video now, have a go at those questions and then come back when you're ready to go over the answers.

Question one, describe how scientific evidence has led to ozone in the ozone layer reforming.

Your answer may include, scientific evidence was used by governments who in an international treaty, called the Montreal Protocol, agreed to phase out the use of CFCs.

And this ban on CFC use has reduced the breakdown of ozone, and the hole in the ozone layer has not only stopped increasing but has started to reform.

Question two, state two alternatives to CFCs.

And your answer may include hydrochlorofluorocarbons, or HCFCs, hydrofluorocarbons, or HFCs, pump sprays instead of aerosols or nitrogen as a propellant in aerosols, or ammonia as a coolant in fridges.

Well done if you were able to answer both of those questions correctly.

We have reached the end of today's lesson, so let's summarise some of the key points from today's lesson on Ozone Layer: A Story of Global Success.

The ozone layer protects life from harmful ultraviolet radiation from the Sun.

Chlorofluorocarbons, which are known as CFCs, were once used in many products, and when they entered our atmosphere, they reacted with ozone, and ozone has the molecular formula O3.

Ozone levels decreased, but scientific communication led to action being taken to prevent further loss of ozone.

And the work of analytical scientists suggest the ozone layer is now reforming.

Well done.

You've worked really hard in today's lesson.

I hope you've enjoyed it and I look forward to seeing you again in another lesson soon.