Checking City Air

26 April 2009

Interview with

Jo Dicks, Cambridge City Council, air quality monitoring

Helen Scales -   This week we are looking at the things that you might find in the atmosphere and later on we will be joined by Steven Ashworth who is using lasers to look at the chemicals above the ocean and find out how these contribute to environmental chemistry.  But first Ben Valsler met up with Jo Dicks.  He is a Scientific Officer for Cambridge City Council, to find out how they currently monitor the air we breathe in urban environments.  

Ben Valsler - Monitoring levels of environmental pollutants is vital, not just for scientists to understand what's going on in our atmosphere but also for everybody that walks past the bus station, anybody that wants to build a new building, everybody who thinks that we need a new car park - and so I had met up with Jo Dicks, he is the Principal Scientific Officer for Cambridge City Council, outside one of their monitoring stations.  So Jo, what do we have here?  

Jo Dicks -   Well here we have two units measuring PM-10, which is small particles, and oxides of nitrogen both of which are in this location predominantly vehicle pollutants and we are quite close to the bus station and this is actually the site at which we measure the worst pollution in Cambridge currently.   

Ben Valsler -   Well we can certainly hear lots of buses going past us and we're next to a huge green box, how does this actually work?  

Jo Dicks -   Well this particular monitor draws air in through a filter which separates out the smaller particles.  It then collects the dust on a filter which is on the end of a glass tube which vibrates at one frequency, as dust is deposited on that tube the frequency changes and that's what the device actually measures.  

Ben Valsler -   So the change in the frequency of this vibration will tell you what mass of particles you have that you are collecting from the air?  

Jo Dicks -   Absolutely, that's what it measures - mass and gives it in real time.  

Ben Valsler -   So this can measure the particulates that might be coming out of back of buses or various other sources, what else do we measure here?  

Jo Dicks -   Well we measure oxides of nitrogen and NO2, nitrogen dioxide in particular is the one that we have a health based standard for.  In Cambridge we actually have air collision management area because of high levels of NO2 which is only formed by combustion and principally it is formed by vehicle combustion in the city, that's the main source here.  

Ben Valsler -   So right here we have the one measuring center, are there more of these across the city?  

Jo Dicks -   Yes, we have got five locations like this, one is at our office which is part of a national network and four others fairly central.  

Ben Valsler -   So how do you actually collect the data for this?  Does somebody have to come around and plug themselves in, or does it transmit back to you at the council?  

Jo Dicks -   No, we've got a modem link to all of these sites and it's actually collected by a contractor who then quality assures that data and sends it back to us.  We do get a daily digest of the information but we also then get six monthly and annual ratified data sets.  

Ben Valsler -   How much does one of these cost to run?  

Jo Dicks -   Well, they cost about £50,000.00 in capital outlay to buy the whole set and then about three or four thousand pounds a year to service.  

Ben Valsler -   And this will give you a good measure around each and every one of these signs but obviously we'd like to know in a bit more detail about what might happen say to somebody walking through Cambridge town centre?  

Jo Dicks -   Absolutely, and we are very interested in people's actual personal exposure to air pollutants and a fixed site like this - whereas it gives you a good picture of what's going on at that particular location, it's very poor at showing what day-to-day exposure people actually get.   You are then looking at someone's actual exposure, you are also seeing where the high points of exposure are and that could then dictate which route they take to avoid these peak areas.  

Diffusion TubeBen Valsler -   So once we have this sort of information, the information you are collecting from these base stations as well as potential information from somebody walking around with a handheld monitor, what can we use this for?  

Jo Dicks -   Well we can use it to inform planning decisions and also perhaps cycling, walking routes but also where we then monitor in the future - we wouldn't want to be putting a great deal of new housing into an area that's already got very poor air quality without mitigating that in some way and likewise you wouldn't want to be sending extra buses along a road that's already heavily polluted.  

Ben Valsler -   So if I was proposing building a new shopping centre somewhere around Cambridge City Centre, what would I have to do to make sure that you say it's okay to build it?  

Jo Dicks -   Well you would certainly be required to meet air quality assessment and that would involve monitoring the background levels prior to developments and then modeling the impact of the developments upon the air quality situation locally.  At the moment we would ask for a small diffusion tubes survey to be carried out and to inform us of the background levels and that particular locality.  

Ben Valsler -   How do the diffusion tubes work?  

Jo Dicks -   Well, a diffusion tube is just a very simple device, it has a small grid with a bit of reagent on it which we then hang on a lamp post, it absorbs pollutants, in this case nitrogen dioxide, over the period of exposure and then it get sent off to a lab to be analysed.  So it gives us maybe one day to point a month or one day to point a fortnight depending on how often you change the tube.  

Ben Valsler -   So I have found the site that I want to build my shopping centre, I have put a series of these diffusion tubes around and I have given you three months worth of data showing how much nitrous oxide there is in the air, what next?  

Jo Dicks -   We would then ask the area to be modeled, I mean use this dispersion model and which is mathematical modeling but it requires validation with monitoring information so we run a model with the new traffic flows in place and use the diffusion tube data to validate that model.  But diffusion tube data, it's very low resolution, it's not very accurate, you get sort of plus and minus 20% accuracy with this.  So it's extremely ball-park and it's not very good for validating models.  The devices that we have been working on recently would enable much greater data resolution, much greater accuracy temporal resolution and it would allow us to pinpoint the areas where the pollution would be worst.  

Ben Valsler -   And so with this higher resolution data you can far more accurately predict the impact that my new shopping centre would have?  

Jo Dicks -   Absolutely, and we are talking about very, very small changes which can make a great deal of difference.  

Ben Valsler -   So what do you see as the future of environmental monitoring?  

Jo Dicks -   Well obviously these fixed sites with very accurate reference methods are always going to be important.  We have got 11 years' worth of continuous data from these sites in Cambridge which is a great wealth of information but a combination of much more mobile monitoring and a greater special array across the city undoubtedly form our decisions better in the future.  

Helen Scales -   That was Jo Dicks, Principal Scientific Officer for Cambridge Council explaining that although static environmental sensors give us constant high quality data of how clean our air is, they are rather expensive and they can only tell us about the air immediately around where they are placed.  

Cambridge City Council put the latest information on air quality online - to check it out, go here:


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