On the Road with Mobile Sensors

We sent Meera out and about in Cambridge to find out how to monitor the atmosphere on the move...
26 April 2009

Interview with 

Prof. Rod Jones & Dr Mark Calleja, Cambridge University


Traffic at a standstill in a traffic jam on a motorway


Helen -  You are listening to The Naked Scientists with Chris Smith and me, Helen Scales and we have heard a lot about the portable sensors that Rod Jones and his team are using to monitor pollutant levels whilst walking around a city.  So lets now join Meera to see how these sensors actually work in action.  

Meera Senthilingam -   Yes, so I am now here at the Chemistry Department at the University of Cambridge with Rod Jones and we've got one of these handheld devices in front of us and there's a lot packed in here so what have we got here, at the top we've got the three sensors, what are these sensors detecting?  

Peak hour traffic on the Monash Freeway, Melbourne.Rod Jones -   Well the three that you can see here are detecting nitrogen dioxide, nitric oxide and carbon monoxide.  Inside each sensor there's a small amount of fluid which is called the electrolyte and when the gases enter the sensors that actually forces very small current to flow in that electrolyte and you measure the current so you can relate the current from this which is very small, to the amount of gas that you are trying to detect, and of course this box does rather more than that then because what it has to do is to take that current and digitize it so that we can then transfer it to a computer.  

These boxes actually also determine where we are using GPS that everybody knows, and in fact there's a blue tooth connection here which then links it to a mobile phone which is sitting just next with me now and it's that mobile phone which transmits the data from the sensor in real time to a central computer so that we can look at it.  

Meera Senthilingam -   Now you have managed to pack all of this into not only a light box but it's size is actually quite small, it's only about 15 cms by about 5 cms - and you are going to take me on a particular route around Cambridge so we can see these devices in action.  Where are we going to go?  

Rod Jones -   Well we're going to go from the Chemistry Department which then enters immediately a busy road.  We are gong to walk towards a major traffic junction and then into an area which is green park area really.  These are typical of the kinds of places that we have been making these kinds of measurements.  

Meera Senthilingam -   We are outside the Chemistry Department now with the handheld monitor.  Rod, how are you going to turn it on?  What should we do before we start our walk?  

Rod Jones -   Well I have just turned the phone on and it now shows the screen which I can then use to detect the sensor box.  On the sensor box I am just switching on that by pushing one single button and in a minute, there we are, it's telling us that the device is working and has actually detected the GPS satellites.  So we are now ready to go.  

Meera Senthilingam -   Okay, so lets go.  We are heading down towards a particularly busy junction.  Now I can imagine that the sensor will be particularly active right now.  

Rod Jones -   Well yes, the chemistry of the atmosphere is really quite complex.  A lot of these vehicles are going to be releasing a fair amount of nitric oxide and so we'd like to expect to see really quite high values of nitric oxide and of course individual cars have very different emission a month.  So and the age of it already matters as well that if a vehicle is old and not particularly well maintained, it is quite likely that the emissions from that are going to be much higher.  

Meera Senthilingam -   It is very busy here.  There are numerous cars, motorbikes, lorries, trucks just going by but now we are going to head over into the quite Parkers Piece.  

Rod Jones -   It's very interesting because if we are trying to understand how the chemistry of the troposphere works, we actually have to look at a lot of different sources and immediately you can see that we have trees and greenery here, all of which can emit a range of different molecules which can affect the chemistry of the troposphere.  So we need to get the complete picture and this little box is part of that process.  

Parker's Piece CambridgeMeera Senthilingam -   We are now in the middle of Parkers Piece, which is a very large green area here in Cambridge.  Now it is much quieter, the cars are much further away but you know, they are still not that far so surely the pollutants are still going to be reasonably high here.  

Rod Jones -   That's right, and in fact we can feel a slight breeze, that's obviously going to bring the pollution from the road which we can see just over there into Parkers Piece.  We are not likely to see quite as big fluctuations in the emissions from vehicles because they have now tended to mix out a little bit.  

Meera Senthilingam -   As pleasant and sunny as it is here we now are going to go back to the lab in order to look at the information of this particular ride.  

We are now back on Rod Jones's lab in the Chemistry Department but joining me now is Mark Calleja who is a software developer on the project.  So Mark, you've got your laptop with you here and it's got Google Earth on it so on your Google Earth now we've got a satellite view of the area that I just walked with Rod.  What are you going to show me on this particular view of Cambridge?  

Mark Calleja -   Right, here we are going to have a time-dependent plot of someone walking around with a sensor and we are going to just show the nitrogen dioxide track and just to show the difference between walk inside the quiet street or next with a traffic laden street.  We have colour-coded data points so those from dark blue low pollution to pale blue to white for medium levels of pollution, going up to pink and dark red means high levels of pollution.  

Meera Senthilingam -   So this particular video we are going to watch is just showing one person wandering around Cambridge, the person is shown on the map as a circle and the circle is moving around as the person is moving around Cambridge.  Now to start with, this circle is dark blue which means that the pollution levels are actually quite low.  

Mark Calleja -    It so happened at that time yes it was.  It's mainly dark blue for the routes this person has chosen except when he gets to quite a busy street which is just off Parkers Piece and then he starts going to pinks and reds.  That's not unusual, wherever you get high levels of traffic that's when you expect your pollution levels to go high.  As you can see as he go down to the bystreets the pollution levels drop.  

Meera Senthilingam -   But as you say, this is for a very specific moment of time.  So how can you collate this information into something a bit more usable?  

Mark Calleja -   What we'll do is we can plot all data points from a time window on one graph and impose our graph on the relevant map from Google Earth and that will allow us to have a more fuller picture what happens over say a day or a week.  

Meera Senthilingam -   And Rod, actually you've got one of these graphs full of the particular route that we walked today.  It is basically a series of lines around the city and it looks like a wall or something has been built around it and variations and the height of this wall are basically the variations in certain pollutants.  

CamMobSens - Carbon Monoxide in CambridgeRod Jones -   Well that's right, as Mark was saying what we have done here is just a plot on top of the Google Map a vertical line which represents the amount of pollution at a particular point and so as an individual walks around the streets you can see a line which follows the mocking and the height of the line above the surface represents the amount of pollutant, in this case, carbon monoxide.  

And here in Gonville Place that was the place that we stood with all the traffic flowing around, in fact we see the highest amount of carbon monoxide around two parts per million which is way, way above the natural background.  But you can now see where these sensors really come into their own.  So if we now look at our map of nitric oxide what we see in fact is really very high concentrations of NO, close to where the bus station is, but now when you follow our walk into the center of Parkers Piece, surprisingly the nitric oxide values drop really quite low.  

What it means is that we are further away from the vehicles which are the primary nitric oxide sources but now if we look at NO2 which is one of I guess of considerable concern in terms of health, we certainly see that the NO2 values in the middle of Parkers Piece are in fact every bit as high as in the surrounding areas, and in the sense we expect that because what we are saying is the reaction of nitric oxide with ozone to give us NO2 and so the NO2 values kind of hold up as you move away from the direct pollution sources.  CamMobSens - Nitrous Oxide in Cambridge

But everything actually depends critically on the subtleties, the wind speeds, the meteorology, the specific vehicle that passes you by.  

Meera Senthilingam -   What you are going to do with this information in the future?  Could it be the case where someone could just log on and plan their route according to the levels of pollutants they see?  

Rod Jones -   Well that's one of the ambitions I think of this project so that anybody, anywhere can actually determine by looking at the web what their likely pollution exposure is going to be.  

Helen Scales -   So if this technology develops further you could have a clear picture of where pollutants are highest and therefore where to avoid not in your own city but many cities around the world.  That was professor Rod Jones and Dr. Mark Calleja showing Meera Senthilingam just how these portable sensors work and how we can use the data with Google Earth to get a detailed map of local pollution.


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