Will expanded London emissions zone cut air pollution?

The scheme has come under scrutiny from some car users in the capital
01 September 2023

Interview with 

Frank Kelly, Imperial College London


Car exhaust pipes


The detrimental effects of poor air quality on our wellbeing are widely acknowledged by public health bodies. There are 2 main types of air pollution which impact our health: nitrogen dioxide gas, or NO2, and tiny soot particles. Owing to its size, London is a particularly poor performer internationally, nearly always exceeding the safe levels of these pollutants as defined by the World Health Organisation. Motor vehicles are one of the primary producers of air pollution, so reducing traffic emissions is seen as a key way to tackle the problem. The latest ULEZ expansion, now covering the whole of Greater London, is the latest initiative in a 20 year history of congestion charges in the capital. Critics argue that the expansion punishes people with older cars too severely, while others question if it will have much of a meaningful impact on air quality at all. Chris Smith spoke to Imperial College London’s Frank Kelly to hear why he thinks the most recent ULEZ expansion is justified. He leads the London Air Quality Network project, a system of monitors across the city which measure air quality on any given day…

Frank - So when the inner London ULEZ was introduced after it had been in operation for one year, we looked at the data and we found that across all the major roads, the gas nitrogen dioxide had fallen by about 46, 47% compared to the year before the ULEZ was up in operation. So it had a big effect on that particular pollutant. The other one, which we worry about, the tiny particles of dust, the PM2.5's, had fallen as well. Not as much as NO2, probably around 20, 25%. So yes, there is evidence that if you bring in controls to eliminate the more polluting vehicles, then in due course you will get an improvement in air quality.

Chris - But that's been the bone of contention, hasn't it? Because it seems there's almost an arbitrary line in the sand where cars of a certain age can come in, cars of a greater age can't come in, electric vehicles are completely exempt and some people are arguing, well, electric vehicles, we regard them as highly green, but in fact they pollute in a different way. They're heavier, they produce more tire wear particles, they also produce more brake wear particles. So we may just be robbing Peter to pay Paul in pollution terms.

Frank - Well, there is a lot of very solid evidence, which has shown that the exhaust emissions, particularly from diesel vehicles, are particularly harmful to our health. So there is a very good reason to try and control the number of older diesel vehicles on the roads. So that is, I think, a very robust policy. The issue that we have is that we still, yes, we'll replace those older vehicles with newer ones and as you rightly say, any vehicle will produce powerware particles, brake wear particles, and it'll words on the road surface as well. So the actual solution to our air pollution problem in cities is actually not just making cleaner vehicles use the road, but actually to have fewer vehicles using the roads. And that really points to better public transport systems.

Chris - Others have pointed out that there's only so far you can go with stopping people or trying to stop people using the roads because the pollution will still blow in from elsewhere. So unless you've got clean air everywhere, you're still going to get some pollution.

Frank - So it is true that pollution doesn't respect any boundaries. And this is why you really need solutions, not just at the city level but also at the national level. And at the international level, we have to ensure that specific negotiations go on with our neighbours. In particular, we know that in the spring and early summer there are a lot of pesticides and fertilisers used in the agricultural system, not only in the UK but also in Europe. And these can end up being entrained up into the air. They get carried in the winds over to ourselves. So we do need two things to happen. We need improvements in our agricultural systems and emissions and we also need to recognise that we need to do this not just by ourselves, but in combination with our international partners.

Chris - Notwithstanding that, the other thing that people are objecting to is the fact that polluting cars can still carry on polluting. They just pay a bit more. And some people are saying, if we were really serious about the pollution problem, we would just ban them. Whereas at the moment it happens to be a quite convenient revenue stream for the mayor of London.

Frank - I honestly think that that's an unfortunate view to take. The ULEZ would be most successful actually if it wasn't making any money at all, because then none of those vehicles would be on the roads of London anymore. We already have 90% of the vehicles that are compliant and can legally use the roads. We just want to try and remove that final 10% and we're doing that by saying, you can use it if you will pay this extra money. So it's a deterrent. It's not a 'you must stop doing this'.

Chris - And do you think that London is a special case or we're probably going to see this sort of thing being implemented using London almost as a guinea pig in other major cities in the UK in the near term.

Frank - Yes. I think it's 15 cities across the UK which have what are called clean air zones. And they operate in various ways. Some of them, like the ULEZ, will charge a vehicle owner a daily fee if they use their vehicle on the roads. Others will only be in operation during certain times of the day and others will just be a deterrent to certain types of vehicles. I think London is at the vanguard, it is the guinea pig. It is important that London shows that these sorts of schemes can benefit not just simply from an air quality improvement point of view, but actually from a health point of view as well, because ultimately that's why we're going through this angst at the moment. There's 500,000 people with asthma in greater London and many of those require medications on a regular basis and require more medication when pollution levels increase. So ultimately that has to be the benefit. And if London can demonstrate that, then I think others will follow.


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