They believe that the particles – a type of iron oxide called maghemite – have been largely ignored in the past due to their diminutive size. But a new type of pollution analysis using magnetism has discovered the particles in Underground ticket halls, platforms and operator cabins.
Since it takes time for iron to oxidise into maghemite, the results suggest that pollution particles are suspended for long periods, due to poor ventilation throughout the Underground, particularly on station platforms.
Some of the particles are as small as five nanometres in diameter: small enough to be inhaled and end up in the bloodstream, but too small to be captured by typical methods of pollution monitoring. However, it is not clear whether these particles pose a health risk.
The researchers believe that periodic removal of dust from Underground tunnels, as well as magnetic monitoring of pollution levels, could improve air quality throughout the network.
Multiple studies...