Harpers Ferry is covered in smoke during the steam era. What you don't or might not know is that there is a 1100 foot cliff rock face directly above this portal. A great deal of water comes down when the rains move west to east.
The engines running westbound would be pulling hard before a series of grades.
There was a time the other Portal was flooded almost completely through back in the 70's? Anges if memory serves. They played a Canoe either in a picture or TV on the water near the top of the portal... something like 25 feet up.
In my days of trucking the only time I saw black smoke was two situations, running a natural air breathing engine without a computer in sight working hard or a failed intercooler clamp on a computer controlled engine. The result would be smoke that has to stick to everything with oily substances.
There were entire strips of hard coal/coke country where green was replaced by grey/black of the fires.
The word Telltales show me a post with a series of ropes to warn brakemen riding atop of cars that there is a tunnel coming and not far away.
I hope that this contributes in some way.
