What IS all that black stuff?...

This is why they have to treat road runoff as sewage. I would be curious exactly what is in that stuff. Some oil, to be sure, and some stuff worn off the road itself. Some rubber from tires. Some normal dirt and dust from the environment.

Yep, our lungs, and in many cases, it goes into the cracks on pavement and buildings too. When I was starting a community cleanup project in LIC we kept sweeping this grey/black sand-like material out of the streets. It took a few days, but eventually I realized it was carbon particles (plus some fun air toxics from diesel) precipitated out of auto exhaust.

Try this experiment in Manhattan- take a piece of white tape and stick it to the outside of a building. See how black it gets after a week.