Don't forget rubber tires grinding against asphalt at high speed. Or brake pad dust. We're already at the point we know it's bad to spend much time near highways (say, living within a few hundred feet of them) but haven't, as a culture, really decided to do anything about it yet. Probably because we're too all-in on 55+ MPH roads, so far as infrastructure, so the cost to fix our mistake would be too high.
Staying at a rental that is next to a residential street, the city is very clean and air is great. The street has somewhat alot of traffic and I noticed that the table outside we eat on gets dirty very quickly. Like in one day a wipe on it is black and filthy from the street which is behind a hedge 20ft away.
The balcony of the flat where I live at is unusable because of the major street next to it. There's this same greasy dust everywhere. My guess is that it is soot, covered with unburnt hydrocarbons, from car or oil heating exhaust. It's really disgusting. I have resigned long ago to not let plants intended for consumption grow there...
