I remember in the early 90s in China. Buildings got deliveries of coal to burn for their boilers. Out during a rainstorm in Beijing I came inside literally dirt

I remember in the early 90s in China. Buildings got deliveries of coal to burn for their boilers. Out during a rainstorm in Beijing I came inside literally dirty with black soot (either the rain had nucleated around the soot particles, or it washed them out of the air).