Lesson video

This lesson is called Atmospheric pollutants and is from the unit Atmosphere and changing climate.

Hi there, my name's Mrs. McCready and I'm here to guide you through today's lesson, so thank you very much for joining me today.

In our lesson today, we're going to describe how pollutants can be produced by impurities in fuels and by incomplete combustion.

Now, we're gonna come across a number of keywords today, and they're listed up on the screen for you now.

You may wish to pause the video to make a note of them, but I will introduce them to you as we come across them.

Now, in our lesson today, we're going to first of all look at pollutants that are found in the atmosphere, before we consider the problems that these pollutants cause.

Then we're gonna look at some solutions, including catalytic converters and hydrogen fuel.

So, are you ready to go? I certainly am.

Let's get started.

Now, when we consider what pollution is, we usually consider things that we can see.

And if we're considering atmospheric pollution, we usually consider that smoky smog that we can see into the atmosphere being produced by car fumes, being found in cities on smoggy days, and coming out of industrial chimneys as industrial smoke.

Now, all of these are very tangible things, very real things that we can see that can clearly make an impact on our environment, but actually, pollutants also include many harmful particles that we can't see, and we are inhaling them all of the time regardless whether we can see them or not.

Now, pollutants can be made naturally by processes such as volcanic eruptions and forest fires, or by human processes such as through power stations, industrial processes, and through car fumes, for instance.

Now, regardless of how pollutants are put into the atmosphere, they are still nevertheless pollutants.

And in 2019, the World Health Organisation estimated that 99% of the world's population was living in places where their air quality guideline levels were not being met.

So almost everyone in 2019 was living in a place where air quality was too poor to be healthy, as defined by the World Health Organisation.

Now that is a really big problem which needs to be addressed, and we'll look at some of the detail of that next.

So which statement about pollutants is incorrect? Is it A, pollutants such as volcanic ash can be made naturally; B, pollutants such as sulphur dioxide from power stations can be made by humans; or C, all pollutants are visible to the unaided human eye? I'll give you five seconds to think about it.

Okay, so you should have said that the statement which is incorrect is C.

Well done if you did.

So what I'd like you to do is just to quickly summarise the first part of our lesson by stating two sources of atmospheric pollutants made by humans and naming a natural source of atmospheric pollutant as well.

So pause the video and come back to me when you're ready.

Okay, let's check your work.

So two sources of atmospheric pollutants made by humans.

So you might have mentioned car exhaust fumes, smoke from industrial plants, power station emissions, that sort of thing.

And a natural source of atmospheric pollutant, well, you probably listed volcanic eruptions or forest fires.

Well done.

Okay, let's move on and have a look at some of the problems that these pollutants cause.

Let's consider carbon dioxide first, because carbon dioxide is a pollutant and it's produced during complete combustion reactions.

So this is where the fuel is burning in sufficient supply of oxygen and all of the carbon in the fuel is converted into carbon dioxide.

Now, carbon dioxide is not just a pollutant, but it is also a greenhouse gas which is contributing to global warming, so it's really quite problematic.

So when we burn a fuel in oxygen, it gets turned into carbon dioxide and water.

Now, if there is an insufficient supply of oxygen available, then carbon monoxide and carbon particulates are produced instead in a process called incomplete combustion.

So this is where there is not enough oxygen available to turn all of the carbon in the fuel into carbon dioxide.

And instead, whilst some oxygen is present, carbon carbon monoxide is produced.

Carbon particulates are also produced.

So this is city ash, essentially, where the fuel has been broken down into very small pieces but has not been burnt properly.

And water is also produced in incomplete combustion as well.

So fuel plus oxygen leads to carbon plus carbon monoxide and water, and this is called incomplete combustion.

Now, carbon monoxide is a particularly harmful gas because it is colourless and odourless and extremely toxic, and the very fact that it is colourless and odourless makes it very, very difficult to detect.

But the problem is that it diffuses into our blood and binds irreversibly with the haemoglobin in our red blood cells.

Now, haemoglobin normally transports oxygen around our body and provides therefore oxygen to all our living cells for them to get on and do their job through respiration.

If carbon monoxide has bound to the haemoglobin instead of oxygen though, then oxygen is now no longer available to the respiring cells in our body, and this can cause fainting, coma, and even death.

It's really very problematic.

Fortunately, it's detectable, so it's very easy to fit a carbon monoxide detector alongside the device which is combusting a fuel to make sure that carbon monoxide is not produced, and the detector detects carbon monoxide if it's present and alerts us to the presence of carbon monoxide so that we can then do something about that.

We can get the heater, the boiler, whatever it is, serviced and fixed and make sure that it is burning fuel with complete combustion rather than with incomplete combustion.

I said the other problem with incomplete combustion is the production of particulates, these city particulates, which is essentially unburnt fuel, but they've been broken down into very, very small pieces.

Now, particulates are particularly nasty because they lead to respiratory problems and also can cause heart disease.

So they create this ashy residue within the atmosphere, which then goes on to irritate our body.

They also prevent light from penetrating all the way through the atmosphere because they're dirty and they absorb light and reflect light back into space.

Now, this phenomenon is called global dimming, which you would think was perhaps a good idea actually because what it's doing is stopping so much sunlight from getting into the atmosphere and therefore reducing global warming.

Unfortunately, the health implications of particulates is far greater than the benefit gained from global dimming itself, and so incomplete combustion with the problems of producing carbon monoxide and the city particulates is really quite an important one to overcome.

So which of these is an impact of increased levels of carbon dioxide in the atmosphere? Is it global warming, respiratory problems, global dimming, or death due to inhaling toxic gas? I'll give you five seconds to think about it.

Okay, so the impact of increased carbon dioxide levels is global warming.

Well done if you spotted that.

What about the impact of increased levels of particulates such as soot in the atmosphere? What is the impact of this? Okay, so for particulates, you should have said respiratory problems and global dimming.

Well done if you spotted both of those.

Let's have a look at another pollutant now, sulphur dioxide.

So sulphur dioxide is produced when fuels which contains sulphur impurities are combusted.

So we're reacting sulphur with oxygen to form sulphur dioxide.

Now, sulphur dioxide can react with the oxygen and water in the atmosphere to produce acid rain, and acid rain is problematic for two reasons.

One because it can harm living organisms, and secondly because it can react with limestone buildings and eat away at them, damage buildings, and cause them to erode.

Sulphur dioxide is also a problem for respiratory health in humans because it can irritate the lungs and cause respiratory illness.

So sulphur dioxide has a good number of problems associated with it as a pollutant.

And let's look at another group of pollutants, nitrogen.

Now, oxygen and nitrogen are both present in great quantities in the Earth's atmosphere, and at high temperatures they can react together, such as within a car engine, for instance.

Now, when nitrogen and oxygen react together, they produce nitrogen monoxide and nitrogen dioxide, and these collectively are representative by NOx, because it's monoxide and dioxide.

Now, both of these, nitrogen monoxide and dioxide, can then go on to react with oxygen and water much like sulphur dioxide does and therefore also produce acid rain and therefore have the same implications that sulphur dioxide does as well, both to living organisms, to limestone buildings, and also to the respiratory health of humans.

So acid rain produced by nitrogen monoxide and dioxide and also sulphur dioxide can cause problems to living organisms, limescale buildings, and also to human respiratory health.

So, increased amounts of sulphur dioxide in the atmosphere causes what? Respiratory problems, global dimming, acid rain, or global warming, what do you think? I'll give you five seconds to think about it.

Okay, so did you say that sulphur dioxide can cause respiratory problems and acid rain? Well done if you did.

And what about an increase in the amount of oxides of nitrogen in the atmosphere, what might that cause? So hopefully you said for that the same problems, respiratory problems and acid rain.

Well done.

Okay, to summarise that, what I would like you to do is to complete the table, filling in the missing pollutant names, pollutant formulae, and the problems associated with those pollutants, as the gaps show.

Then I would like you to consider the fact that petrol and diesel fuels which are used for cars naturally contain carbon, hydrogen, and sulphur atoms, and inside the car engine they combust in excess oxygen at high temperatures.

So bearing all of that in mind, what I would like you to do is to firstly predict which atmospheric pollutants may be produced, and then write a chemical equation to show how each pollutant is produced.

So pause the video and come back to me when you're ready.

Okay, let's check our work.

So firstly, I asked you to complete the table.

So you should have completed carbon monoxide and stated that its problems are that it's a toxic gas that can cause death.

You should have added CO2 in as the formula for carbon dioxide and stated that this contributes to global warming.

And for the particulates of soot, the formula is C for carbon, and the problems caused by soot include respiratory problems and global dimming.

Then for the fourth row, you should have said that acid rain and respiratory problems is an issue of sulphur dioxide, which is SO2.

And the final one is oxide of nitrogen, that's NOx, and these also have the same problems, acid rain and respiratory problems. So well done if you've got all of that correct, but do fill in any gaps if you have any.

Then I asked you to predict what atmospheric pollutants may be produced from the car engine, and you should have included carbon dioxide, sulphur dioxide, and oxides of nitrogen, nitrogen monoxide and nitrogen dioxide.

And then I asked you to write chemical equations to show each of these pollutants, and you might have included the fuel plus oxygen leading to carbon dioxide and water, sulphur and oxygen leading to sulphur dioxide, nitrogen and oxygen leading to nitrogen monoxide and nitrogen dioxide as well.

Well done if you got all of that.

Let's now move on to look at some solutions to atmospheric pollutants.

So let's start off by looking at catalytic converters.

Now, there are plenty of scientists around the world who are working very, very hard indeed to help come up with solutions to reduce air pollution, and one of those solutions was the catalytic converter.

So most cars now are fitted with a catalytic converter, and a catalytic converter is fitted to the exhaust of a car, and what it does is reduce the amount of harmful pollutants that are being released into the atmosphere by breaking them down into less harmful pollutants before they leave the car engine via the exhaust.

So you can see at the bottom of the car on the underneath of the car at the very back of the car this silver cylinder, and that's the catalytic converter, and this is what is doing this conversion work.

So what is it doing? And what it's doing is reducing the amount of carbon monoxide and nitrogen oxide compounds which are being released into the atmosphere.

So it's converting these pollutants, carbon monoxide and carbon oxides, into carbon dioxide and nitrogen.

So it's taking carbon monoxide and nitrogen monoxide and turning it into carbon dioxide and nitrogen.

So the oxygen is being removed from the nitrogen and bound to the carbon monoxide to form carbon dioxide, leaving the nitrogen on its own, and nitrogen is plentiful within the atmosphere, so it's simply adding to the nitrogen in the atmosphere.

Now, carbon dioxide is being produced as part of this reaction because carbon dioxide is much, much less harmful to humans than carbon monoxide and nitrogen monoxide.

However, it is a greenhouse gas.

So although it has no health implications, it does have global implications instead.

Catalytic converters are really interesting structures.

They have this complex honeycomb structure that increases the surface area over which the exhaust gases pass.

So the exhaust gases are coming into the catalytic converter on the left-hand side of the diagram on the screen and leaving on the right-hand side.

And the honeycomb structure is covered in a layer of catalysts such as platinum and rhodium, and platinum and rhodium are able to accelerate the speed at which the conversion of carbon monoxide and nitrogen monoxide are converted into carbon dioxide and nitrogen.

So the hot gases come in from the engine into the catalytic converter and then are processed by the catalysts and released as the less polluting gases out via the exhaust of the car.

And the catalysts, the platinum and the rhodium which cover the surfaces of the honeycomb structure of the catalytic converter, what they do is speed up the rate of the reaction.

They're not used up in the reaction, but they are speeding it up.

That's why they are called catalysts.

That's what catalysts do and that is why this whole system is called a catalytic converter, because it's converting carbon monoxide and nitrogen monoxide into carbon dioxide and nitrogen using a catalyst.

So, catalytic converters reduce the amount of which gases released from car exhausts, carbon monoxide, carbon dioxide, nitrogen monoxide, or nitrogen? What do you think? I'll give you five seconds to consider.

Okay, so you should have said that carbon monoxide and nitrogen monoxide are the gases which are reduced in quantity by a catalytic converter.

Well done.

So I'd just like you to summarise that piece of learning by completing two tasks.

Firstly, platinum and rhodium are catalysts used in catalytic converters, but what is a catalyst? And secondly, I'd like you to complete the word equation to show a reaction that happens inside a catalytic converter.

So pause the video and come back to me when you're ready.

Okay, let's check our work.

So firstly, I asked you to describe what a catalyst is, and you should have said that a catalyst is a substance that makes it easier for a chemical reaction to take place, it speeds up a chemical reaction, and it is not used up in the process.

Then I asked you to complete a word equation to show what happens inside a catalytic converter, and you should have said that carbon monoxide and nitrogen monoxide are converted into carbon dioxide and nitrogen.

Well done.

Okay, let's have a look at the last piece of our lesson, which is about hydrogen fuel.

So hydrogen is an alternative fuel that could be used instead of petrol or diesel, and therefore used to reduce air pollution whilst providing energy to make vehicles move, for instance.

Now, the advantage of hydrogen fuel instead of petrol is that it firstly releases much more energy per kilogramme of fuel, so you get more energy from hydrogen than you do from petrol for the same amount of mass, and it only produces water when it is combusted.

Well, water is not a pollutant, as we well know, and so it's very, very clean.

So hydrogen and oxygen would combine together to form water.

Now, that sounds like an ideal solution.

Why on earth aren't we using that already? Well, the problems of using hydrogen fuel instead of petrol include the manufacturing process of hydrogen.

Hydrogen uses an enormous amount of energy that could release carbon dioxide into the atmosphere.

So in order to be able to create sufficient quantities of hydrogen to be used as fuel, we have to burn something else in order to make it, so the problem is simply displaced elsewhere.

Also, hydrogen is incredibly flammable and it therefore needs to be stored very safely and securely in highly pressurised containers.

It is certainly not a safe fuel, not that fuels are necessarily safe anyway because they combust, because they burn, but hydrogen is particularly explosive.

So using hydrogen as a fuel replacement for petrol sounds like a great idea, but actually comes with many technological challenges instead.

So which of the following is an advantage of using hydrogen fuel in cars? A, the manufacture of hydrogen requires lots of energy; B, it only produces water when combusted; or C, it needs to be stored in highly pressurised containers.

I'll give you five seconds to consider.

Okay, so you should have said that the advantage of using hydrogen fuel in cars is that it only produces water when combusted.

Well done.

So what I'd like you to do is just to summarise this final part of the lesson by describing one advantage and one disadvantage of using hydrogen as an alternative fuel in cars.

So pause the video and come back to me when you're ready.

Okay, let's see what you've concluded.

Well, an advantage would be that it releases more energy per kilogramme of fuel, or that the only product is water.

And our disadvantage would be its flammability or the need for highly pressurised storage containers.

And also of course, the large energy requirements that hydrogen has for manufacturing it, which could result in carbon dioxide production instead, because that energy has to come from somewhere.

So did you get one of each of those? Well done if you did.

Okay, we've come to the end of our lesson now, so thank you very much for joining me.

In our lesson today, we've seen how air pollutants may be particulates or invisible gases that can cause damage to the environment and often result in health problems as well.

Now, these pollutants can be made naturally by volcanoes and forest fires or by a number of human processes.

Incomplete combustion of fuel can also produce particulates and toxic gases such as carbon monoxide.

And the problem with particulates is that these not only cause health problems, but they also contribute to global dimming by reducing the amount of sunlight reaching the Earth's surface.

Now, complete combustion of a fuel produces carbon dioxide, which is a greenhouse gas, and this contributes to global warming, so whichever way we burn a fuel there will be problems with it.

But we can circumvent some of these problems by using something like a catalytic converter to reduce some of the pollutants from vehicles, but they don't reduce the amount of carbon dioxide emitted, so we still have this problem to contend with.

So I hope you found that an interesting lesson, certainly plenty to think about.

Thank you very much for joining me today and I hope to see you again soon.

Bye!.