Should you live near one of those big noisy "freeway" things you may note the little black particles over everything in the surroundings but nobody likes to tear down the interstate.
Lots of urban areas in the US have been resisting, tearing down, and/or relocating major roads since the freeway revolts of the 1970s:
https://en.wikipedia.org/wiki/Highway_revolts_in_the_United_...
First, I live 150 yards from a major freeway - I-90 in WA, it's three lanes in each direction here. There are no tiny black particles over everything in surroundings, and my outdoors AQI (from my own sensor) is normally in single digits and basically only ever gets above 50 if it's wildfire smoke or the neighbors are burning something.
But second, if we developed a reliable and cheap way to, say, teleport people over long distances, why not tear it down?
As to why some beings need to be whisked hither and yon with such haste, and thus spend quite a bit of time (and energy) trying to be somewhere, anywhere else, well, are they hungry ghosts? Or maybe they min/maxed for wizard and ended up with only three points in wisdom?
smaller stuff is more dangerous and goes deeper into your body:
- PM10: inhalable dust entering the nose and mouth.
- PM4: respirable fraction that can reach the gas-exchange region.
- PM2.5: fine particles that penetrate deep into the lungs.
- PM1: ultrafine particles with potential to translocate beyond the lungs.