Is the London Underground a Worse Air Pollution Than the Exhaust?

Overground in London is ranked as one of the worlds worst or was cities for air pollution. These are nanoparticles generated inside the London underground when you have the metal of the train tracks rubbing past each other. They're effectively rust particles if they're bits of iron oxide, aren't they? Yeah, essentially. There's increasing work being done on this. It puts a whole new emphasis on the advice to wear a face mask on London Transport.