 While I’m all in favour of cleaner air, and wish I hadn’t got a diesel for a second vehicle, I’m not sure that the Labour party’s claim that ‘nearly 40 million people in the UK are living in areas where illegal levels of air pollution from diesel vehicles risk damaging their health’ (Guardian) is particularly meaningful. This is both on the grounds of how the data they have is constructed, and also on how pollution affects real, mobile human beings.
The first part is partially down to this concept of ‘area’. As a counterpoint, I’ve seen it written that ‘99% of the UK meets European air quality standards’, and we know that this is because it is for geographical area as opposed to population. The 1% that does not meet the standard is where lots of people live. However, it seems that the Labour figures are merely a repetition of a parliamentary question from October. This produced a list of ‘Local Authorities with exceedances of NO2 annual mean limit value’ based on a 2015 exercise*. This exercise appears to have itself (at least where I live) on data from 2014, which comes from numerous sensors across the area. However, in the original (LA level) report for my local authority we find that the NO2 average is exceeded at five locations in two smaller geographic areas inside the borough, with six sites in three locations coming close. This is out of 38 monitoring locations across the whole borough. Thus, for each area, the Labour analysis only tells us that at least one location went above the limit, but it could be just one or it could be all of them. I, therefore, count as one of the people living in an ‘area where illegal levels of air pollution from diesel vehicles risk damaging their health’, but I live in a relatively rural location quite a way from the nearest sensor that detected a breach. Indeed, given that sensors are placed next to main roads, and not by a random sample, the numbers of people living within a specified distance of a breach is also a function of the geography of the area. Indeed, what counts for health is not the indicator of the monitoring station, but how much pollution is present in each person’s air. Presumably there is some sort of diffusion gradient for the pollutants, and the breach figure somehow relates to the potential for danger to someone near to it, but also to the danger for everyone else living further away. Indeed, the breach figure for the sensor is 40µg/m3, but research shows that risk comes from breathing in lower concentrations: I guess the assumption is that no one is living on top of the sensor, and that people are living a distance from those highest polluted spots. Better research would assess the level of pollution in people’s homes. There is, of course, some kind of diffusion gradient for the humans too. We don’t sit in our houses breathing the same body of air all the time, but we move about. I spend some time in places much nearer to the monitors with breaches, as that’s where the shops are, but not much. I also go to other cities and travel through more polluted areas. However, the relationship between the population’s exposure to pollution and the exceedance of the annual NO2 average is not clear: if the breach is in the town centre it is shoppers that will experience it, and if the breach is on a dual carriageway then it is drivers. Once again, the connection is down to the spatial configuration of the place. What is likely, however, is a relationship between income/ wealth and pollution, which goes back a very long way. The configurations of some cities came about because of the way the wind blows: the least desirable places to live were those where the factory smoke blew. At that time a big house next to a main road was desirable, however. Now the pollution mainly comes from vehicles, a house next to the main road is far less desirable, and those who can afford it maintain a healthy distance from those sites with bad air. Suffice it to say, I’m not expecting the plan that the government has been forced to publish to clear any of this up. As ever, one set of politicians want the problem to ‘just go away’, ideally for no cost, and the others want to use the data as the stick to beat the former. *We could also ask why NO2 and not particulate pollution has become the focus of the debate. In the borough I discuss PM10 (particulates <=10microns) is measured at only one site, and annual average limits are not exceeded, which I presume gives a different story for politicians and activists. If it’s not measured, it doesn’t exist!
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