Uber is completely off the radar right now, I think they only service some parts of chaoyang even, I do most of my travel from haidian to chaoyang. Didi zhuanche offers better cars, but not Audi (maybe you are thinking of Shanghai?)...at best a VW or Buick.

Taxi is quite ok when the air is really bad. You can only filter so much air in a car, and it's not like they are putting in giant HEPA filters. The main problem I have is sleeping with the window closed when the air is bad...even with the air filter going, it is very hard to sleep soundly.