According to a study that was published in Scientific Reports, air pollution on the London Underground is frequently composed of ultrafine magnetic iron oxide particles that are smaller than 500 nm.
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The London Underground is an 11-line, 270-station train system that runs throughout Greater London, and approximately 45% of the network is underground. Hassan Sheikh and colleagues examined 39 dust samples from the London Underground were examined to determine their structure, size, shape, chemical composition, and magnetic characteristics.
Platforms, ticket booths, and train operator cabins along the Piccadilly, Northern, Central, Bakerloo, Victoria, Northern, District, and Jubilee lines were some of the locations where samples were taken in 2019 and 2021. Major stations like King’s Cross St. Pancras, Paddington, and Oxford Circus were included in the sampling.
According to earlier studies, magnetic iron-bearing air pollution makes up 50% of the particles in the London Underground. The iron-containing particles in the authors’ samples, according to their report, were mostly made up of the iron oxide known as maghemite, which had an average diameter of 10 nm and a diameter range of 5 to 500 nm.
With diameters ranging from 100 to 2,000 nm, some particles were arranged into larger clusters.
The authors propose that traditional air pollution monitors, which may overlook the number of ultrafine airborne particles in the London Underground due to their low weight, could be supplemented by magnetic monitoring approaches similar to those used in this study to characterize air pollution particles.
Previous studies have suggested that iron-containing particles are created when train wheels and brakes come into contact with train tracks and that heavier loads and faster speeds can create finer particles.
The abundance of ultrafine maghemite found in dust samples from the London Underground, according to the authors, could be due to iron-containing compounds from wheels, brakes, and tracks being exposed to the air for longer periods due to inadequate ventilation and then being resuspended in the air when trains pull up to platforms.
They suggest washing the tracks and tunnel walls, utilizing magnetic filters in ventilation systems, or installing screen doors between platforms and trains to reduce the amount of resuspended dust.
Sheikh, H. A., et al. (2022) Magnetic and microscopic investigation of airborne iron oxide nanoparticles in the London Underground. Scientific Reports. doi:10.1038/s41598-022-24679-4.