Transport bosses have been urged to reduce pollution on the London Underground network after it was found to be 30 times higher than on busy roads in the capital.
The Committee on the Medical Effects of Air Pollutants (COMEAP) warned Transport for London it was “likely that there is some health risk associated with exposure to underground PM” – tiny particles known as particulate matter.
In its first study looking into the issue since 1998, COMEAP found underground particles were larger in size and concentration than those in outdoor air above ground.
Researchers found that a person travelling on a bus for two and a half hours was exposed to a third of what they would be travelling on the Tube for just an hour.
Unpublished data from King’s College London also showed that Hampstead station on the Northern Line had the highest levels of pollution.
Tests recorded an average of 492 micrograms per cubic metre (μg/m3) of air on the station’s platforms, compared with an annual average of 16 μg/m3 from a roadside monitoring site in the capital.
An average of 4.8 million journeys are made on the London Underground every day.
The report found that the London Underground was affected more than any other subway system because it was the oldest and due to “deep, poorly ventilated tunnels”.
The committee concluded that there was likely to be some health risk associated with using the Underground system – but that a lack of studies into this made it impossible to determine the extent.
It added that further investigation was required into the toxicity of the dust breathed in by tube passengers, which is heavier and more metal-based than the smaller, carbon-based particles in the air above ground.
“We would encourage Transport for London to continue to find practicable ways of reducing PM levels on the Underground network,” the committee said.
Professor Frank Kelly, chair of COMEAP, said people should continue to use the tube given the relatively short time spent underground and lack of evidence of harmful effects.
He told The Guardian: “We’ve got all this information about the health impacts of the particles above the surface.
“Below ground, we know we have a higher mass but of a different type – we don’t yet have the research into the level of the toxicity, and hence the health risk.”
