Science Centre: Carbon Dioxide Pollution

Dave Ansell and Ginny Smith use cabbage juice to show what effect carbon dioxide has on the atmosphere...
25 October 2013

Interview with 

Dave Ansell and Ginny Smith, The Naked Scientists


Crushing the red cabbage with a little water


Dave Ansell and Ginny Smith use cabbage juice to show what effect carbon dioxide has on the atmosphere, with Tehnuka Ilanko and Crushing red cabbageArwen Deuss.

Ginny -  Who knows what this is?  Anyone eaten one of these before?  No?  No one's ever had... oh yeah, there's a couple over there.  So, we've got a red cabbage here.  Now, you might wonder what that's got to do with extreme Earth.  Well, red cabbage actually has something in it which can act as a pH indicator.  So, it can tell you whether things are acid or whether they're alkaline.  Now, that relates back to earlier when Tehnuka was talking about what comes out of volcanoes.  As well as the lava, you get all these different gases and some of those gases can go up into the atmosphere and they can actually cause acid rain.

Dave -  Although what we're going to end up using here isn't really a major part of acid rain at the moment.  So, what we're going to do is we're going to take some water and see what happens to it if you add one of the big acids, which Tehnuka was talking about, is carbon dioxide.  And it's also gas we're pumping into the atmosphere all the time as we drive around in our cars and run our power stations.  So, what I've done is I've taken this cabbage, and I spent about an hour with Tom at the back there, mashing it, and then I kind of squeezed water into it and I've made a nice bottle full of cabbage juice.

Ginny -  Just what you want for your dinner, nice bottle of cabbage juice.  It's a beautiful purple colour actually.  I think you could probably market that.

Chris -  Does it taste nice?  You drunk it.

Dave -  It tastes of cabbage.  If you like raw cabbage then this is obviously the drink for you!  So, there's this slightly bluish tinge to it because Cambridge water has got lots of dissolved chalk in it.  So, it's slightly alkaline and what I've got here is a device for dissolving lots of carbon dioxide in water.

Ginny -  So, when you buy a fizzy drink, that's made fizzy because they've dissolved a load of carbon dioxide inside it.  It's kept at quite high pressure in the bottle and then when you open the bottle, the pressure is released, the bubbles can come out and you get your lovely fizzy drink.  But this is a machine designed to make drinks fizzy.

Dave -  So basically, what it's going to do is inject high pressure carbon dioxide into the water.  Do you want to volunteer? Does anyone want to do the injection?  Do you want to come up?

Ginny -  A round of applause for our volunteer please.  What's your name?

Millie -  I'm Millie.

Ginny -  Brilliant!  So, what are we going to get her to do?

Dave -  So, well if you just press the button there and if everyone else watches what happens to the colour of the liquid, go for it.

Ginny -  That was a slightly rude sounding noise.

Dave -  So, has anyone noticed a change in colour?

Crowd -  Yeah.

Ginny -  So, what's happened, Millie?  Can you see what colour it's gone?

Millie -  It looks the same to me.

Ginny -  She was behind when it was happening.

Chris -  Let's try that again.

Ginny -  Can we put there more through?  Have a watch while Dave puts some more in.  So, you should be able to see that it's starting going slightly more pink in colour.  It was quite a bluey purple and it's now quite a sort of pinky purple.  Brilliant!  Thanks a lot, Millie.  You can take your seat.

Dave -  So, this means that after you dissolved carbon dioxide in water, it becomes acidic because a pink cabbage juice means it's turned into an acid.  This is quite important because it's what creates caves, so you dissolve carbon dioxide in water, that makes it slightly acidic and it will dissolve the limestone and dissolve out sort of tunnels in the rock where water is flowing and make caves.  It can also be a big problem with the carbon dioxide we're pumping into the atmosphere, because actually it will make the sea more acidic, which makes it much harder for creatures with shells in them to grow a shell, because there's all this acid in there trying to dissolve it's shell off all the time.  So, it could cause all sorts of problems for the oceans.

Ginny -  And when we have volcanoes releasing things like sulphur dioxide, which will do a similar thing - they'll dissolve in water but form a much stronger acid - then we can get the acid rain that you may have heard of that dissolves buildings and statues, and that sort of thing.

Chris -  Ginny, thank you very much.

Ginny -  And if anyone wants any fizzy cabbage juice, we've got some here.

Chris -  That's the next experiment, to drink it and see what happens.  Any questions?

Ed -  I'm Ed from a town called Swavesey.  I was just wondering if there's ever been such like bad acid rain to kill anybody or badly injure anybody.

Ginny -  Not that I've heard of.  I think the concentrations that you get in acid rain are low enough that it doesn't tend to.

Dave -  I guess the one time when you might produce something nasty, is if it comes out of a volcano - which is why I'm looking over at the volcanologists over there! You get lots of nasty gases coming out of there.

Tehnuka -  The gases themselves can definitely be harmful and the acid rain can also be very damaging to the environment.  I'm not sure if there have been any cases of someone being directly killed by acid rain.

Ginny -  I think it's more likely to cause damage if you inhale the gases and they actually get inside you rather than once it's dissolved in the rain, it's kind of diluted a bit, so it's not going to be as dangerous.

Dave -  And the reason why they're actually really quite dangerous is they create essentially an acid inside your lungs, and that attacks your lungs, these gases.  So, carbon dioxide is fine, but things like sulphur dioxide can do really nasty things to your lungs.

Chris -  Tehnuka, you do get situations where you get lots of gas dissolved in a lake, for example.  We've heard of examples where lakes suddenly burp up a huge load of, say, carbon dioxide and it will then engulf a local populace, and people drown effectively in CO2, don't they?

Tehnuka -  There was a case of this.  I think it was in Lake Nyos in Cameroon where a lake overturned and a whole lot of carbon dioxide that had been inside it came out and killed everyone overnight.

Chris -  Arwen, I've got an email over here from someone called B. R. Shorten.  It refers to a story a few years ago about an earthquake in Italy where a whole bunch of toads disappeared before the earthquake happened, and these toads always congregate when there's a full moon to mate at a certain time of year.  There's evidence showing that they began to congregate, but then a little bit before the earthquake struck, they all vanished inexplicably.  It wasn't until the last aftershocks had past that they began to come back.  Do you think there's any possibility that there could be something going on that these creatures are tuning in to?

Arwen -  Perhaps, it's really difficult to predict earthquakes.  And yes, there have been anecdotal stories about animals responding to it like the toads.  Will it be really useful for us to predict an earthquake?  That's another issue, because if you want to predict an earthquake, you want to be very sure that that earthquake is going to happen.  It's difficult to watch the toads.  They might be moving away for some other reason and then you have evacuated the whole city, the earthquake didn't happen, people will get very upset.  They'll get back to their houses, the earthquake might be 2 days later, but they're back.  They won't listen to you anymore.  I think it's a very difficult business.  So yes, they might have some sensitivity to some vibrations, but how that is really working, very unclear and not a very safe way to predict an earthquake.

Ben -  Hey, I'm Ben from Cambridge and I was just wondering, you were talking about acid rain dissolving statues.  Is this an intermediate threat at the moment or is it in the future?

Ginny -  So, that has actually happened.  There are places in America where they have taken to covering over their statues during the winter to stop that from happening.  It's the same thing - if you've ever looked in your kettle, there's a kind of scum, sort of almost like bits of rock in the bottom, and that's calcium carbonate.  What's happened is that has come out of the water that it had been dissolved in.  What's happening with the statues is kind of the opposite.  When the rain is acidic, it can dissolve that calcium carbonate which is limestone, which a lot of stuff is built out of and that can really wear away statues.

Dave -  It was a big problem, 20 or 30 years ago, but people who've run power stations and cars and things put a lot of effort into especially removing sulphur.  So, that was one the big things which made acid rain.  They scrub it out of the chimneys of the power stations and they actually extracted it out of things like diesel, so it's not actually in fuel which you put in your car.  So, certainly in Europe, it's much less of a problem.  I imagine it's still a problem in China because they're less far on in the clearing up states than we are.

Aron -  Hi.  Aron from Hardwick here.  My question is, would you say that acid rain's main cause is from volcanoes or inefficient car engines?

Ginny -  Well, as we were just saying, it definitely used to be power stations when they were burning coal and just chucking it all out.  You know, you hear about the London pea souper smog - it was really awful, the kind of emissions.  Then I would say it would definitely have been that.  Now, we're cleaning things up a bit more.  I'm not sure.  Do you have an opinion?

Tehnuka -  I'm not sure.  I think that I suspect industrial cause is a bigger factor.  With volcanic eruptions, generally, if you have a big volcanic eruption, you have a lot of other things to worry about.  Acid rain probably isn't the immediate priority.  Even with things like hydrogen fluoride coming out of a volcano, for example, in the case of Iceland that I mentioned earlier, this big Laki eruption that lasted a long time: the fluorine caused poisoning of crops and of the cows.  That's not necessary caused by the rain, it's caused by the fluorine.  So, among all the other things you have to worry about, I think acid rain from volcanoes is lower on the priority list.

Ewan -  Hi.  It's Ewan from St. Neots.  My question is, if acid rain were to fall on a lake, what would be the case that would happen?

Ginny -  Well, if a lake becomes too acidic then it can be really bad for the fish living there.  If it becomes too acidic, they can't survive and for any other creatures living in the lake, it's not good.  But it depends how big your lake is because if you've just got a small amount of acid rain going into a big lake, it's not going to be very acidic overall.

Dave -  It was one of the things which caused everyone to clean up their power stations in Europe.  There were a lot of lakes in Norway and Sweden which were getting poisoned because of it.  But I think they've got a lot better since we stopped pumping out lots of acidic gases from our power stations.


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