We asked an expert if we should be worried

Air pollution in Copenhagen Metro is higher than on the most polluted stretch of road in Danish city.

New measurements from the University of Copenhagen found that concentrations of ultrafine particles underground were 10 to 20 times higher than near Town Hall Square in the city.

“Our measurements show that the metro is probably the place in Copenhagen’s public space where you are exposed to the most concentrated air pollution,” says Professor Matthew Johnson, lead author of the study.

It is just one of many studies that have been carried out in recent years looking at pollution on underground train networks.

The French Agency for Food, Environment and Occupational Health and Safety found that metros in the country had three times the outdoor air pollution. Research on the London Underground has found ultrafine metallic particles small enough to end up in our bloodstream.

So why is such pollution a problem i metro train systems and is it something we should be worried about?

Why does pollution increase in metro systems?

Professor Frank Kelly is head of the Environmental Research Group at Imperial College London – a global center dedicated to air pollution research.

He calls the issue with metro systems a “box problem”.

“Imagine that the pollution that is being generated is entering a relatively small amount of air, which is the underground system itself,” he explains.

AP Photo/Alastair Grant

A man sits on a bench waiting for a tube train at Westminster Underground station in London. – AP Photo/Alastair Grant

“Although the pollution generated above the ground is going into a huge amount of air, so it is diluted very quickly.”

A 2020 study surveyed the entire London Underground system. The bottom line of his findings was that the deeper the train line, the worse the pollution.

This is a lack of ventilation – a problem that many cities are aware of and are working hard to solve.

Where does pollution come from in the metro?

Most of the Air pollution in metro systems usually PM 2.5 (tiny particles with a diameter of less than 2.5 microns).

On the London Underground, this pollution is mainly composed of metal particles – mainly iron and copper.

These are generated from the wheels running on the rails. The connection between the trains and the electrified railway also creates a small amount of particulate pollution.

But Professor Kelly says the pollution it creates is unique to the environment and is different in other metro systems.

Some networks have rubber wheels, for example, which create their own form of pollution as they rub against the rails.

REUTERS/Sarah Meyssonnier

Passengers stand on a platform at Saint-Lazare metro station in Paris. – REUTERS/Sarah Meyssonnier

Should we be worried about pollution in metro train systems?

Professor Kelly calls it “the million dollar question”.

Most of the research conducted on the health effects of air quality made above ground. But the composition of the underground pollution is different.

“The jury is still out on whether it is very harmful to our health, [somewhat] harmful or of no real consequence,” says Professor Kelly.

“Common sense would suggest that it probably has some impact but we can’t really say how much.”

Studies are currently underway on the London Underground to determine the effect of tube journeys on sensitive people lung conditions. They are also looking at the health records of the staff who work there like guards who stand on the platforms all day.

Professor Kelly says we probably won’t have the “big answer” for at least another year.

So should we avoid metro trains because of the pollution?

For many, the only alternative to catching a metro train is to get into the car.

“It’s well established that above-ground pollution is bad for your health, we know that,” says Professor Kelly.

He also said that if you are sitting in your car in traffic, unless you have your air intake during recirculation, you really are. poisoned by the car in front.

And some of the most polluted parts of our cities are where there is double lane, slow traffic. It is even worse on those roads which are frequented by heavy duty commercial diesel vehicles.

Images Vuk Valcic / SOPA/Sipa USA via Reuters Connect

Increased traffic is seen on the roads in King’s Cross, London. – Images Vuk Valcic / SOPA/Sipa USA via Reuters Connect

“Being in heavy traffic is not an alternative that one would want to choose for any other exposure such as the London Underground,” says Professor Kelly.

It is better, he says, to get where you need to go in the least polluted way.

Professor Kelly also emphasizes that networks such as the London Underground are valuable public resources and operators such as Transport for London recognize the need to solve the problem.

“We have to keep it and improve it,” he concludes.

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