Rarefied Air

I've always like this phrase - "rarefied air". I like it used in terms of something fancy, esoteric, or better than usual. So imagine my surprise to find out it also means 1. (of air, esp. that at high altitudes) Containing less oxygen than usual. 
So basically all the air in Los Angeles is rarefied! One of my husband's suggestions was that I stick to running before work in the morning (6:30am!) because there is less junk in the air before everyone in LA starts driving around. I pointed out that early in the morning was also when I slipped on ice, had burning lungs, and frozen (and now fractured) fingers and nose. To which he said "I have a ski mask you can use". Yes, because what a beginning runner needs is to be mistaken for a burglar fleeing the scene of a crime.
So my third run took place in the afternoon, using a new route I plotted using Google Maps. I tried to anticipate a path that would have nice, even sidewalks and no hills to slow me down / pool water.  What I found out is that all the sidewalks in Los Angeles are crappy, even in the "rarefied" neighborhood adjacent to ours.  Basically it's like the planners planted trees without considering where the roots would eventually grow. Then they laid concrete over it for sidewalks, with a sort of "we conquered this" aplomb. And 80 years later, the trees are like "F*ck you."
I kept thinking of Craig T. Nelson in Poltergeist "You moved the headstones, but you never moved the bodies!"