Perspectives: finding hidden pollution on the London Underground

and what to do about it

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Researchers from Cambridge University have found a method for measuring previously hard to detect pollution particles using magnetism. Previous studies had found that concentrations of particulate matter (as small as one twentieth the width of a human hair) on the London Underground are higher than those in London more broadly (above ground). However, those studies may have even been underestimating overall pollution levels given that some of the smallest particles have been historically hard to measure. Those tiniest particles are so small you would need 7,000 of them piled on top of each other to equal the width of a human hair!

There is plenty of evidence pointing to the harmful health impacts of ultrafine particles and in particular magnetite particulate matter.

This study had concluded that because of poor ventilation in the Underground, the maghemite rich dust could be re-suspended in the air when trains pull into platforms making the air quality worse there than in either driver cabins or ticket halls. Possible remedies suggested include placing screen doors between platforms and trains, as there are on the Jubilee Line and Elizabeth Line, regular cleaning of the tracks and tunnel walls and including magnetic filters in ventilation systems.