To be fair, "cities are the exception with bad air" neglects the reality that cities are the default for where people live. So the "air near people" is generally city air.

That said, I live in SF and my AQI is usually <50. Not as great as 5, but we sometimes get down to single-digits. Cities don't have to have bad air.

That depends, really. If you have an inversion layer going, you can get pretty poor air quality in lots of locations because people use crappy wood-fired stoves that produce a lot of particulates.

That does happen occasionally where I live, last night for example. But it's only a single digit number of days out of a year. The rest of the time air quality is very good.