In 2019, a Financial Times investigation declared the London underground “the dirtiest place in the city”, with parts of the Central Line between Bond Street and Notting Hill Gate having more than eight times the WHO limit for PM2.5s. Tube dust is particularly high in iron oxide from the metal brakes and rails, but it’s not only mechanical. “A lot of the dust in this environment is coming from the passengers themselves,” Alno Lesch, operational manager for track cleaning, told the Financial Times, pulling out a black tangle from under the train platform. Human hair. Empire of dust: what the tiniest specks reveal about the world - The Guardian
All I can say is yikes.
