Peter Walker writes a blog in The Guardian about the problem that urban air pollution poses for cyclists in London, although the problems exist in many if not most major cities. This week we are seeing unbelievable levels of pollution in cities such as Beijing and the thought of cycling is daunting.
Air pollution: how big a problem is it for cyclists?
It prematurely kills around 30,000 Britons a year, but at least on a bike there are measures you can take to reduce the risks
It’s a scenario familiar to any urban cyclist: you’re stuck behind a fume-belching bus or taxi, a choking diesel aroma wafting through your lungs. You think: is this really the healthy option?
The good, if simple, answer from pollution experts is: yes. Cycling does remain many, many times better for your health than not cycling, even factoring in exposure to pollution and the risk of accident. What’s more surprising is that on two wheels you might even be exposed to less of the smelly stuff than those using other forms of transport.
The more full answer is, inevitably, slightly mixed. Air pollution is a very real danger, with even conservative estimates gauging it prematurely kills almost 30,000 Britons a year, making it the most deadly public health hazard apart from smoking.
And yet, experts say, there are a range of measures cyclists can take to limit their exposure, from taking quieter back routes, to cycling at particular times of the day. There’s even an argument that pollution masks, once common in cities like London but little seen these days, might help. But more of that later.
Gary Fuller, an expert on air quality at King’s College London, notes that the villain behind most of the peril in urban areas is the diesel engine. While petrol vehicles have somewhat cleaned up their emissions in recent years, diesels still emit lots of particulate nasties like black carbon, and are increasingly common in new cars. He says:
People should be worrying about diesel traffic and particle exposure, and also about nitrogen dioxide. The thing about these is they haven’t really improved in urban areas for the last decade or so. We’ve managed to clean up air pollution emissions in terms of nitrogen dioxide from petrol cars.
Buy a petrol car today and it will emit about four-tenths as much in oxides as a car you bought 10 or 12 years ago. But for diesels, despite the fact we have ever-tighter emissions standards the conditions in which the emissions test is performed doesn’t really reflect the real world.
It is, Fuller adds, a national issue:
It’s not just a London problem. You can go out into apparently rural areas with an A-road travelling through a small village and you can find EU limits being exceeded.
That said, the way people are exposed to airborne pollution is not as straightforward as you might think. Fuller’s KCL colleague, Ben Barratt, carried out a test in which a group of Londoners – an ambulance driver, a cycle courier, a toddler, a pensioner, an office worker and a school pupil – spent the same 24-hour period fitted with GPS trackers and an instrument to measure their exposure to black carbon.
Barrett stresses this was no more than an illustrative demonstration study, but the graph of cumulative exposure is nonetheless interesting, with the cycle courier encountering the second-least amount of less black carbon overall, and being exposed to less than the ambulance driver during work hours as a proportion of the total day.
A graph produced by Ben Barratt of King’s College London shows the cumulative exposure to black carbon. Photograph: King’s College London
There are other factors at play, Barratt says, not least the ambulance driver’s longer working hours, and the different levels of exposure depending on where people lived. However, he says, it does seem that cycling helps dissipate smog through movement in the open:
A lot of it is about ventilation, and the cycle courier is in a big, open air room, whereas the ambulance driver is in an enclosed box.
Obviously, if you’re replacing dirty air with dirty air it doesn’t make much difference, but with this particular pollutant you’re very susceptible to individual, filthy diesel vehicles, and that’s what the ambulance driver is picking up, I think.
There is, of course, another big factor at play: Barrett’s study measures exposure, not dosage, and a cyclist is likely to breathe more heavily, which could increase the amount of black carbon ingested. Conversely, in a busy city like London a trip by bike can be much quicker than, say, its equivalent on a bus, which can reduce exposure all over again.
As an aside, Barrett notes the relatively small amount of daytime pollution exposure for the office worker, despite the fact they are based in central London. This is, seemingly, because their office is mechanically ventilated:
It’s not necessarily just where you are. It’s a combination of where you are, what you’re doing, and what time of day you’re doing it.
So, as a cyclist, what can you do to limit your exposure? One simple idea is to take quieter back streets, where the concentration of some pollutants can be considerably lower than on main roads. As an illustration, the London Air Website provides a live map of smog levels in the capital, showing how so much of it is clustered around big roads.
Fuller also advises riders to consider when they cycle, especially in the summer, when ozone tends to peak in the afternoon, and can have a significant impact on lung function:
Ozone follows a distinct diurnal pattern. It’s always greatest in the mid to late afternoon. It’s not so much for urban cyclists but if you’re looking to have a day out on the bike maybe think about travelling in the morning and then the evening, avoiding the mid afternoon on the hottest, most polluted days. That can reduce your exposure quite a lot.
Ozone build-up is the reason endurance events at the London 2012 Olympics, like the marathon, were mainly scheduled in the morning.
Yet another KCL academic, Ian Mudway, an expert on respiratory toxicology, points to studies by Edinburgh university in co-operation with academics in Beijing, which appeared to show that masks can filter out some smog.
The lessons are not entirely clear, he stresses, not least as the masks used were closer to industrial ones than cycling masks, while Beijing’s pollution is more severe even than London. He says:
Having read those papers I wouldn’t say they have no benefit. I might say that people who wear them probably overestimate the benefits that they’re delivering, but I think there’s enough in that paper to say they make some difference.
Fuller reiterates that the risk from pollution is often underestimated. He cites a questionnaire sent by smog campaigners to MPs, asking them to list a series of public health hazards. Air pollution was, he says, consistently and wrongly placed at the bottom.
It’s an illustration of how the perception of risk isn’t fully understood. I have a feeling cyclists perceive the risk form pollution more than the general public, because they have a much more intimate association with it, much more visceral.
As ever, all this needs to be placed in context. And the context is clear: cycling is, on balance, very good for you even in big cities.
A study last week in the British Medical Journal said London’s hire bike scheme had brought a clear net benefit to health, as activity outweighed the risks from pollution or crashes. An earlier study on Barcelona’s equivalent bike hire scheme, published in the British Medical Journal, estimated the system saved the city an average of more than 12 lives a year overall.
But pollution is still a worry. I have a habit of leaving home sufficiently late that I usually end up cycling to the office along the most choked main roads. There is a perfectly good route which guides me mainly along the back streets, but takes about ten minutes longer. Maybe it’s time to start thinking about that.