A Pollution Tester for Your Pocket

Professor Rod Jones is a Professor of Atmospheric Physics in the Chemistry Department at Cambridge University. He explained explained how he's developed a pollution detector which fits in your pocket to Chris Smith and an audience at the Cambridge Science Centre...

Rod - Well, I do lots of different things, all the way from looking at the ozone layer, through to looking at climate change. But tonight, what I've brought along is one of the very small sensors that we make so that we can actually look at air pollution and try to understand how air pollution itself works and then we try and build slightly more sophisticated gizmos which allow us to monitor what a person walking the streets might be exposed to.

So, inside this box which the people can see here, those on radio, it's about 20cmx8cmx2cm it's got one nice green button which is the GO button and inside it, there is a mobile phone. I'm going to hand it out in a minute and what this does, it's also got a navigation system inside so that we can know where it is. We have three different gases being measured, somebody can put this in their pocket. We know where they are, we know what they're exposed to.

Chris - How do you know where they are?

Rod - Well, because we've got what's called a GPS aerial inside it, which is what you need in your car satnav to help you navigate. And so, inside here, there's a mobile phone. We have a satnav effectively, and we have some chemical sensors. So, we can actually monitor every second or so, what a person is being exposed to, and then we can relate that back to what we know is causing pollution in the town. We can also relate it back to somebody getting more asthmatic or wheezy as they go through a more polluted area. So, we're trying to conduct experiments which are linking those two.

Chris - Why is this better than what we have already?

Rod - It's better because you'd have a real problem in putting conventional instruments into your pocket. They weigh about 60kg and they're about the size of this table.

Chris - So, how have you managed to make it so small?

Rod - Well, we've taken sensors which are traditionally used in alarm systems and we've just made them better, and about a thousand times more sensitive. We can now make them about a thousand times smaller, which is what you can see here, what the audience can see here. Because we can make them really small, we can now make them much more portable and we can just give them to people to carry around.

Chris - What can you detect with it?

Rod - Well, these little chappies can just detect gases like carbon monoxide and nitrogen oxides. We've got other ones which can do other gases as well, but nitrogen oxide is particularly well-known or thought to be associated with health impacts. So, that's one gas that we can go for.

Chris - Let's take some questions. Get your hands up in the air if you'd like to ask anything. Let's start down here at the front. Who are you sir?

Mujal - I'm Mujal. I live in Cambridge. I just wanted to ask, what is air pollution and how do you measure it?

Rod - Well, air pollution that we're worried about is probably nitrogen oxides which come from cars. It's probably particles that come from cars and buses particularly. A lot of it is linked to transport, but those are the principal gases that you'd expect us to link to air pollution and those are the ones which are monitored by the national networks.

Chris - Who's next? What's your name sir?

Elliott - Elliott. How long does it take to make one?

Rod - Gosh! Well, to design and build one from first principles, it takes a few years. But once you know how to do it, it probably takes a few minutes.

Chris - So, there's hope for you yet, Elliott. You can do it with Lego perhaps. Yes, madam.

Ailish - Hi, my name is Ailish. I live here in Cambridge. I was just wondering you mentioned putting the device in your pocket. How accurate a test would that be compared to breathing in harmful chemicals?

Rod - That's a very good question. Of course, if you put it in your inside pocket, not very accurate. So, what we're actually doing and I've not brought them along this evening is make much smaller versions of these which effectively, you can put on your lapel much closer to where you breathe in. So, we're trying to get closer and as we build these things smaller and smaller, we can put them in much more sensible places.

Chris -  Can I just ask a quick question, Rod? What happens if you put it in your trouser pocket and you've had beans?

Rod - Well, we don't measure methane.

Chris - But isn't that quite an important greenhouse gas?

Rod - It is an important greenhouse gas and in fact, I don't know whether you're trying to lead me into another area, but we've got other sensors just like this which are designed to measure greenhouse gases so that we can for example work out how much CO2 Cambridge is emitting. Not methane yet, but we could go that far, but I'll keep that for another story I think.

Chris - What's your name?

Laura - Laura.

Chris - Hello, Laura.

Laura - Once we've created pollution, can we get rid of it?

Rod - Gosh! That's another very good question. Well, it gradually decays in the atmosphere. Even when it rains, we get rid of a lot of pollution, but some pollution takes quite a few months to get rid of. So, there's a natural process of getting rid of it, but if you're emitting it locally then you can easily get very high concentrations even though you're losing it gradually. It's like filling a bath.

Chris - What's the amount of time that carbon dioxide, once it comes out of the exhaust pipe of a car or whatever for instance stays in the atmosphere once we've released it? How long is it around for causing a greenhouse effect?

Rod - Well, of course, carbon dioxide isn't a pollutant - an air quality pollutant - in the way that we were talking about a couple of minutes ago. But once it comes out of your tail pipe, it's probably in the atmosphere for 100 or 200 years.

Chris - So, anything we emit now, we've potentially got to deal with for 100 or 200 years. We got to live with their consequences for that long.

Rod - Yes, I think that's absolutely right.

Carlo - Good evening. My name is Carlo and I would like to know when we walk in the street, are children more exposed to pollution than adults are because maybe adults are taller or does it make no difference?

Rod - We're looking at that and the effect doesn't seem that great. Of course, if you park your buggy at the exhaust of a bus, you're in trouble. But actually, what's really important quite often is which side of the street you walk on. And so, one of the things we're leading towards doing is developing a phone app to tell you which side of the street you want to walk on if you want to take a low pollution route. So, that's good question.

Chris - That could mean that everyone takes that route and then they walk really slowly because they're all stuck behind the slowest person in the world who is inevitably going to be on that same pavement. Then you get more exposure because you got to breath the air for longer.

Rod - Well, that's probably true so maybe we should...

Chris -  You have to factor that into the app. One more question here.

Errol -  Hi, Errol. How many data points do you actually need to get a good map of a town? So, how many people carrying it for how long to give you a really good sort of map of pollution across say, a city centre?

Rod - We've been trying for years to get that number and we haven't got there yet. Every time we can make a measurement with more sensors, we see more detail. So, we're trying to unpick that problem at the moment.