I’ve lived in London long enough to remember the “black snot” you’d get after riding on the Tube (especially the Northern Line!) back in the early 2000s. They’v

I’ve lived in London long enough to remember the “black snot” you’d get after riding on the Tube (especially the Northern Line!) back in the early 2000s. They’ve done a lot to improve ventilation, and reduce dust from train brakes, in recent years. The air certainly smells and feels a lot fresher and healthier on the extensively-ventilated Tube compared to on crowded buses with little or no ventilation at all.