Less than 20 miles from the AQN offices is a building made from shipping containers in which some of the most important air quality work takes place. We’re at one of the country’s three urban background air quality monitoring ‘supersites’ in South Manchester,
The three sites – the others being in Birmingham and London – were created with funding from the Natural Environment Research Council (NERC) to take our understanding of air quality to a new level. The sites were to feature extremely sophisticated instruments able to measure gases, aerosols and a range of meteorological phenomena.
The Manchester site is run by the University of Manchester and is also affiliated to the National Centre for Atmospheric Science (NCAS). Showing us around the facility was Dr James Allan who, conveniently, works for both.
James originally came to Manchester as an undergraduate in the mid-90s, ultimately doing a PhD, in the Atmospheric Science Group in the UMIST department of physics. And he’s yet to leave.
As someone involved at the very beginning of the supersite concept, he explains how everything came together and why the relatively leafy Fallowfield was chosen as the location. ‘The majority of the time, people are not walking down the street or on public transport or coming into contact with the big pollution sources. The majority of our time is spent at home or in the office, so we’re not exposed to the highest levels of pollution. That’s not to say those aren’t important, but the measurements that we’re trying to get here are representative of a baseline level pollution that you get exposed to by living and working in a city.’
Who’s air is it anyway?
This immediately begs the question of where the air being monitored originates. Much of what is identified has been blown in: PM2.5 and ozone fall into this category. Other pollutants, such as nitrogen dioxide – seen by many as the main pollution problem in Manchester – is local. ‘In theory, particulate pollution from a given source can last weeks and go halfway around the world,’ James explains. ‘In reality, what tends to happen is, after it’s emitted, it’s going to disperse, and the influence of a given source is going to lessen the further you get away from it.
‘But if you’re downwind of say, a big city, you can be hundreds of miles away from a source area and still feel the influence of it. Within the UK, the most polluted periods we get – in terms of things like PM2.5 and ozone – tend to be when the air comes from the south and the east because we’re getting all this dirty air from Europe. But of course, we’re in Manchester so we don’t just get European pollution, we get it from further south in the UK as well.
‘But it really does vary. Under other weather conditions, particularly at night, you might be looking at the pollution spiking up and down and you can be quite confident that it’s a more local influence. Part of the fun of analysing the data is being able to determine where the pollution is coming from.’
Into gear
Needless to say, the equipment being used is very expensive, as James confirms: ‘It’s not cheap, no. And a lot of them are not cheap to run either. You’ve got to keep them fed with various consumables. The other thing that costs money is calibrations, because we need to have all these things measuring accurately. This isn’t the type of measurement that you can afford to do everywhere. And that is one of the things that underpins the Supersite concept, you don’t have lots of sites like these, but you would have some. Yes, it’s expensive, but it’s useful, that’s the idea.’
For consistency, Manchester tries to keep in step with Birmingham and London in terms of the equipment they have access to but there’s the odd bit of equipment one might have that another doesn’t, and one Supersite might opt for a different manufacturer to another. Manchester was also built slightly larger than it needed to be to host what you might call ‘guest instruments’.
As the research has progressed, more kit has been added. A later addition was the Total Carbon Analyser which was making sufficient noise to threaten the recording of our chat.
I speculated that it might analyse carbon. ‘It does!’ James confirmed, to my satisfaction. ‘It tells you how much total particulate carbon you have in the air. So, in combination with other instruments, that’s quite useful when you’re interested in looking at what the particulates are made out of.’
The most recent piece of equipment to have arrived in Fallowfield is an upgraded gas chromatography-mass spectrometer for measuring VOCs, that’s owned and operated remotely by the University of York.
York can do that because everything is set-up so the equipment mostly looks after itself. Human intervention is typically needed once a week, to check everything’s running as it should and to replace bits that need replacing. Otherwise, everything is supposed to be as automated as possible. Indeed, anyone can visit the website to see the data coming off the instruments in real time.
All about the data
But is that data useable by the public, or is it a level or two above their understanding? James is cautious: ‘I’m going to pick my words here, because, yes, it’s the academic world who are the main users, but the data is freely available in the public domain.
‘I suppose the tricky thing about it is that the data that we produce it isn’t necessarily the sort of data that the general public are used to digesting. We do have PM 2.5 but we’ve got loads of data that goes beyond that, and if you present that then people are like, “What am I supposed to do with this?”
‘One that’s often easiest for people to digest is a quantity here called UVPM – ultra violet particulate matter – if that number is significantly bigger than the black carbon, then that is an indication that you potentially have a lot of wood burning smoke present.’
Hold on, this is counter-intuitive. Wood burning is a major source of black carbon, so how does that work? Fortunately, I’m asking the right man. ‘What happens is that when wood burns, the smoke that it emits has a brownish hue compared to black carbon that you would get, say, from diesel soot. So by comparing how much light it absorbs at different wavelengths, you can come up with an informed estimate of the amount of wood burning there is compared to, say, fossil burning.
‘So that is something that people – not necessarily the general public – but what you might call the activists, can look at and say: “it’s a cold winter’s day, there’s a lot of PM 2.5 out there… oh look, it’s wood burning.’’’
This article originally appeared in the July issue of Air Quality News magazine.
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