The London Underground might seem dusty and polluted but the air beneath the capital is safer to breathe than that on the surface. A new report suggests taking the tube might be better for the lungs than cycling or walking.The report published in medical journal Occupational and Environmental Medicine says that while those travelling and working on the Tube will be exposed to greater concentrations of iron oxide, or rust, the level of harmful ultra-fine particles from exhaust emissions is far lower underground.