Why has Glasgow's Hope Street worst air quality in Scotland?

Hope Street is not alone in being a toxic spot for fumes. Across Glasgow city centre, there are other sites where NO2 levels are high enough to be of real concern, and Glasgow is also not alone among Scottish cities in having its polluted sites.

But, as Scotland's worst, Glasgow's city centre makes, according to Dr Ruaraidh Dobson, air pollution researcher and air quality lead at Trilateral Research, a good case study through which to look at the problems of city centre pollution.

He said: “Any large city centre, or any large town which has historically been very reliant on cars, on private vehicles, and on road transport in general, is going to have similar issues.”

To mark Clean Air Day, we looked at the key questions relating to why it is so bad. 

If Hope Street is below legal limits, why are we even bothering with the LEZ?

Earlier this year, there was a great deal of fanfare around the fact that Scotland as a whole now has air quality within legal limits. Even Hope Street, the long notorious "worst street in Scotland" was coming in at just under the statutory limit. 

However, while the site may be within limits, it is only just so, and there are definite spikes across the year which could still have a serious impact on health. It’s also the case that since World Health Organisation guidance is actually for much lower limits in the long run, it is likely that at some point Scotland will lower its legal limits.

Dr Dobson said: “Low emission zones have to be based on statutory legal limits. In practice those limits in the UK are quite high - much higher than the WHO limits. So I think the Scottish government and the UK government should look to reduce those limits. We should look at adopting lower limits over time. That said, you need time for people to change, you need time to get people on side.”

So is it the design of the city that makes Hope Street so bad?

Yes. The combination of tall buildings and grid structure in Glasgow's city centre makes a trap for fumes. This long swoop of tarmac, from Cowcaddens to Argyle Street, dominated in sections by Victorian tenements, and by the towering early concrete Skyscraper, Lion Chambers, holds on to its pollution.

Dr Dobson said, “The problem is the way the built environment has been designed. Anyone who has spent any time at all in Glasgow city centre knows it has a grid structure. It has a lot of ups and downs and very tall buildings so air pollution can get trapped, and can build up during busy times of the day. And it doesn’t just build up on Hope Street. I used to work on nearby Bath Street and I know that the whole area around there is choked with traffic and it’s very noticeable how poor the air quality is. ”

Hope Street. Image: Nick Ponty 

Which other Glasgow city centre streets suffer from bad air quality?

Hope Street is host to the only automatic air quality monitor in the city centre, known as Glasgow Kerbside, a hugely expensive piece of equipment that reports data hourly and is useful for tracking changes throughout the day. But air quality is also measured at sites on other streets through what are called diffusion tubes, which offer a mean value over a period of time, and many of them, too, throw up poor results.

Dr Dobson said: “Renfield Street, Gordon Street, Union Street all have diffusion tube readings over that legal limit. That’s why we have an extensive air quality management area that takes in the centre of Glasgow - because the problem isn’t one street. You can’t just pick one street out. You have to get to the problem at the source and be sure not to just move it around. That’s what hopefully the LEZ will do.”

What can we tell about the impact of the LEZ from the automatic air monitor data at Hope Street?

At only a week since the start of the zone, it’s difficult to say anything for certain. The mean for the first week of the LEZ was 40.9 µg/m3, which is still very slightly over the legal limit for annual mean, though, since emissions vary so much throughout the year it is hard to conclude a great deal from that.

That said, the data is certainly positive. Compared with the first week in June, whose mean was 50.3 µg/m3, this is almost a full 10 µg/m3 lower. However, air quality experts make it clear that it’s hard to tell whether that drop is caused by the LEZ or, for instance, due to the general decline in emissions that would have occurred simply because people were already shifting to newer cars that create less emissions.

It’s also worth noting that since the LEZ was introduced there have been spikes in levels of NO2, peaking at 95.8 µg/m3 on the evening of June 2 and that these were the highest levels in recent weeks.

Are Hope Street and its neighbouring streets really so much worse than other streets outside the city centre in Glasgow?

Yes. If we compare the data from all the other air quality monitoring sites across Glasgow last year, we find that Kerbside is the only one that sits close to or above the legal limit. The others are all closer to 20 µg/m3 and, if we were to set a new air quality limit, might stand a good chance of coming in beneath it.

What overall patterns can we see in the data from Hope Street?

Nitrogen dioxide has been falling since 2010, due to the shift to newer cars that produce less NO2, and the Phase 1 LEZ helped that along by targeting the buses and pushing the Glasgow fleet to become low emissions. A massive drop, for instance, has already been achieved, from an average of 73.2 µg/m3 on the street between 2011 and 2015.  But the reduction has slowed and levelled out around the legal limit of 40 µg/m3. 

What about PM2.5 - is that a problem at Hope Street too?

Two types of air pollution are frequently talked about. One is NO2, which chiefly comes from vehicle exhaust, the other is PM2.5 which is fine particles in the air of fewer than 2.5 microns in size, which come from multiple sources, including wildfires, powerplants and industrial processes. Hope Street's annual mean for PM2.5, which was 7 μg/m3 in fact, doesn't come close to the current legal limit of 20 μg/m3. 

Is the LEZ likely to lower PM2.5 too?

The zone’s purpose is to lower NO2 but is unlikely to have much impact on PM2.5. Dr Dobson did a paper looking at pollution levels during lockdown, and compared them with levels a couple of years beforehand. What he found was that, whilst NO2 came down by about a third, there was little change in PM2.5. "That is,” he said, “because whilst nitrogen dioxide is produced by cars, they’re generally a bit cleaner for PM2.5.”

Do spikes matter?

Dr Dobson says they do. While yearly averages are important, sudden spikes in pollution can have an impact on health too. “If you have,” he said, “a sudden spike in fine particles that causes exacerbation of heart diseases and lung diseases, so even those changes within the day, can be significant for health."

When is the worst time of day for pollution on Hope Street?

Peaks generally happen around 7 pm on a weekday. Sundays are generally lower, because there is less traffic, and weekday daytime NO2 levels are at around their lowest at about 3 pm. 

If there are now very few LEZ non-compliant cars in the zone, where is the NO2 coming from?

Those buses and other vehicles which are compliant, but not electric. All cars running on petrol and diesel release NO2 and, even if the Euro 4 and Euro 6 standards are much better than the older, now-banned cars, they are still contributing to some pollution. For as long as the bus fleet is not entirely electric, it will be producing some NO2. Dr Dobson said: “You can make engines cleaner and you can reduce the amount of nitrogen dioxide but there’s just a limit to what you can do.”

So, are buses still causing the problem?

Retired air quality expert John Lamb has plotted the hotspots for pollution and mapped them to the bus routes - suggesting that it may be buses that are still contributing significantly to the problem.

While it's certainly true that these do match, it should be acknowledged that one of the features of bus routes is that they tend to be the kind of routes that drivers take anyway, because there is a kind of logic about these pathways for getting across the city. Hence, it could still, perhaps, be the other traffic that is the problem.

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What does research tell us about the impact of the pollutants on Hope Street on human health?

Dr Dobson is currently working on a project to model the number of cases caused by air pollution in particular areas.

He said: “There’s a really clear link between PM2.5 and diabetes. Childhood asthma is linked to high NO2 levels. There was, for instance, the tragic case of Ella Kissi-Debrah, in Catford in London who died of asthma exacerbated by air pollution. People often don’t know there is a real cause-and-effect link and we need to make that clear. Some people have died very very early because of the air pollution in Glasgow city centre and we must deal with that. Rather than current policies being an overreaction to that, you could argue that they are an under-reaction to that."

Should all of Hope Street be limited to buses and taxis?

Hope Street has a small section already restricted to these vehicles. Some have suggested that the full length should exclude cars.  However, Dr Dobson observed, this would not necessarily be helpful.  “Not having cars on one street is not going to solve the whole problem. If people are just driving on one street on the end or at the other end, the pollution can just float over. But with the LEZ, I think the zone is big enough and traffic is heavy enough that I think this will have a real and meaningful effect.”