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What causes London’s air pollution, and other smoggy questions

I fear my chronic sore throat may be caused by air pollution – but I’m too nervous to ask the GP. I’m not one of the “very sensitive individuals” that this Defra blog says should be concerned. I am not old, pregnant, nor suffering from a pre-existing lung or heart condition. And even if the pollution is giving me gip, I can hardly expect our over-stretched NHS to prescribe a cure for breathing.

But is it time to ditch my press-on-regardless mentality with regard to air quality? On Monday last week, pollution levels in London were so high that Mayor of London Sadiq Khan issued his first “very high” alert. When levels are this bad, the government’s Daily Air Quality Index recommends that even healthy members of the public “reduce physical exertion, particularly outdoors”.

On a day to day basis, Defra advises that UK air pollution “is not expected to rise to levels at which people need to make major changes to their habits to avoid exposure”.

But London’s most recent pollution-peak is not a one off. Brixton Road in Lambeth breached the EU’s legal limit of annual exposure to Nitrogen Dioxide (NO₂) within the first five days of 2017. And the consequences of long-term exposure, even to low level ambient pollution, are not to be sniffed at. The Royal College of Physicians estimates that outdoor air pollution is a contributing factor in around 40,000 deaths per year. The estimate on the Defra website is 25,000.

So when do the short term effects, such as sore eyes and throat, become symptoms of a chronic health concern? When does an air pollution “episode” become long term exposure?

The short and shocking answer is that if you lived in London for the whole of 2016, then you likely exceeded the limits for long-term exposure to at least one kind of air pollution. According to Timothy Baker, principal analyst at The London Air Quality Network, “the vast majority of London exceeds its long term annual average of Nitrogen Dioxide levels”.

Lawyers from ClientEarth have even taken the government to court over the country’s illegal levels of NO₂ – not just in London, but in 37 out of 43 zones across the UK.

So if you think it’s time to de-smog your knowledge of the subject, here’s what you need to know:


How bad is London, really?

We are used to seeing contemporary images of Beijing’s brown haze or older photos of Britain’s “peasouper” smogs – and, in comparison, London’s recent fog appears a relatively picturesque affair.

But don’t be fooled. According to The Telegraph, at 3pm on Monday 23 January the government’s Air Quality Index hit a peak of 197 micrograms per cubic metre for particulate matter. That’s 190 micrograms higher than the World Health Organisation’s upper safety limit and 7 micrograms higher than notoriously unhealthy Beijing.

What are these pollutants doing to me?

report published last year by the Royal College of Physicians, argued that the serious effects of long-term exposure to air pollution, even at lower levels, “cannot be ignored”. Cancer, asthma, stroke and heart disease, diabetes, obesity, and dementia are just some of the conditions to which air pollution has been linked. There is even evidence to suggest that it may be damaging your mental health.

Young children are particularly at risk. This passage from the RCP report is particularly chilling: “Children living in highly polluted areas are four times more likely to have reduced lung function in adulthood. Improving air quality for children has been shown to halt and reverse this effect. For older people, living near a busy road speeds up the rate of lung function decline that is associated with ageing.”

You can’t see it. You often can’t smell it. So how do we even know air pollution exists?

The government’s Daily Air Quality Index measures for particle pollutants of size PM2.5 and size PM10: this means that the air contains tiny particles of soot (black carbon), metals and other compounds that are either two and one half microns or less, or ten microns or less, in width. It also measures the levels of the gases Nitrogen Dioxide (NO₂), Sulphur Dioxide (SO₂) and Ozone.

DEFRA collects this data from over 300 monitoring sites across the UK, which you can find listed on this interactive map. The most intensive measuring network in the country, however, is run by the London Air Quality Network at Kings College London. The team here uploads hourly pollution indexes for the capital to their website and apps.

What causes it and how can it be stopped?

Timothy Baker from The London Air Quality Network, says that last Monday’s peak was due to a build up of localised fumes, pollution drifting in from the continent, and a period of windless weather that failed to disperse the dirty air.

Some of the localised pollution contained high levels of particles from wood burning fires – possibly from families putting their feet up on a chilly Sunday afternoon. But don’t let the temptation to moan about fire-place owners distract you from the most pressing cause of London’s pollution problem: the nitrogen dioxide emissions resulting from an increased use of diesel cars.

“Diesel is a lot worse than petrol,” says Baker. “Petrol cars over the last twenty years have had their act cleaned up […] but modern diesel cars are only just meeting the same sort of standards that they should have been meeting ten years ago.”

What can I do to protect myself?

Checking the daily air pollution forecasts in your area is a sensible place to start. Then you can decide whether or not to exercise outside, avoid busy roads, or don (as I’m considering) your very own Darth-Vader-style protection mask.

What can be done by others?

There is hope. Last week, Sadiq Khan announced funding for audits that will identity ways London schools can lower their exposure to pollution, while in Paris, authorities responded to pollution peaks by imposing temporary driving restrictions and making public transport free.

But more action is also needed from the government. “The government has consistently failed to deal with air pollution across the UK,” says ClientEarth lawyer Anna Heslop. ““We get these smogs every winter, so besides the air quality plans which the government has been ordered to improve by the UK High Court, we need action in the very short term, especially in our bigger cities.”

In the meantime (cough), I should perhaps take a deep breath and book that GP appointment.

India Bourke is editorial assistant at the New Statesman, where this piece was originally published

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