Particulate Matter Levels in London Underground Are 18 Times as High as the Air Outside

CC BY 2.0. Inside the London Underground/ Lloyd Alter

And the air outside in urban London is pretty awful.

We never used to talk much about little particles of pollution; they were lost in the smog and the cigarette smoke. It was actually thought that they get coughed out of our lungs. Nobody worried about them and, in the USA, they are not even regulated; according to NPR, members of the EPA's Clean Air Scientific Advisory Committee actually "said they do not agree that breathing air polluted with soot can lead to an early death."

Others are not so sanguine about the tiny bits of particulate matter less than 2.5 microns in diameter (PM2.5). We have written before about studies that found that the particles could pass through the lungs into the bloodstream and even into the brain; they can cause strokes and dementia, reduce fertility and increase miscarriages, reduce birthweight, cause heart and lung disease, cancer, and even diabetes. We have noted that particulate pollution is worse than we knew, and is damaging ‘every organ in the body.’

Inside a London Underground Carriage

Inside a London Underground Carriage/ Lloyd Alter/CC BY 2.0

A previous study noted that PM2.5 levels are really high in the London Underground, but now reporters at the Financial Times have taken the particulate matter in their own hands, along with sensitive detectors.

A Financial Times investigation has mapped the air quality in the carriages of the London Underground. Using hundreds of measurements covering 75 tunnel segments inside Zone 1 in central London, the investigation found that levels of pollution on the Underground are dangerously high — as much as 10 times above the guidelines set by the World Health Organization in some parts of the network.

At some points, the levels are 18 times as high as the air upstairs at roadside, and London air is pretty awful.

“It’s very concerning,” says Brynmor Saunders, the lead author of the King’s College paper. “I take the Central line every day, but I would personally avoid it if I were asthmatic.” If the particles in the Underground are as harmful as those outside, then a person who commutes on the Tube for one hour a day would face an increased chance of death as a result of air pollution-linked causes, he adds.
That looks hard to clean.

That looks hard to clean/ Lloyd Alter/CC BY 2.0

The paywalled article is actually fascinating, describing how Transport for London sends out crews to clean the tunnels every night. Most of the stuff they clean up comes from people but "iron is the other big ingredient in the underground haze, caused by the friction of brakes on wheels and wheels on rails."

Also, the history of how the deep tunnels are basically self-ventilating:

Rather than build ventilation shafts along tunnels and at platforms, the engineers who designed the deep tubes planned to use the movement of the trains to circulate the air. Because the trains are nearly as big as the tunnels, they create a piston-like effect as they travel, which engineers believed would be sufficient to keep fresh air in the system. But over time, as dust accumulated, the piston effect instead carried the tiniest, most dangerous particles through the air.

The deeper the tunnel, the higher the level of particulate matter. "The deep tunnels on the Northern line have been particularly problematic, with air that contains 250 ug/m3 of PM2.5 across the entire line, according to the government study released in January, which is 20 times higher than London’s roadside air."

The World Health Organization guidelines suggest that levels average no more than 10 μg/m3 annually, and 25 μg/m3 in 24 hours. However, according to the FT, that may change:

Particulate levels in cities worldwide are “at crisis level now”, says WHO director-general Tedros Adhanom Ghebreyesus, who adds that the PM2.5 level is being revised and “the next one will be more restrictive."

The air in the tunnels may be bad, but the worst particulate matter pollution still comes from traffic. As I noted earlier,

soruces of particulates

IUTA via Ambience Data/CC BY 2.0

There are a million different studies describing what the worst emitters of PM2.5 are, but in cities in North America, it appears that the two biggest are heating and driving. And almost half of the Particulates from driving come from tire wear, road wear and brakes, which is pretty much proportional to the weight of the vehicles, which is another good reason to limit SUVs and pickup trucks in cities and promote lighter, smaller cars. And of course, get rid of diesels, go electric, promote alternatives like bikes and e-bikes, and better transit.

And of course, we need an EPA where they don't talk about PM2.5 today like they did in 1960 about cigarettes.