After a long search, I decided to become member in California Fitness, the gym located in “The Place” on Dong Da Qiao Lu. The place is huge with 400 machines and all the needed facilities. The air seems to be OK, better anyway than in all other gyms visited. The treadmills are good but one of the brands (STARTRAC SoftTrac) does not work well with the Polar transmitter. The other brand (MATRIX MX-T5) works well but has a limited overview of the workout results (no average heart rate, no average incline etc.).
The gym is using the famous Yao Ming player for its brand.
I am running into many former clients from PowerHouse Gym, so it seems I am not the only one to have made that choice.
Only weak point is getting a taxi during the week after the workout. The whole area (CBD west side) is shunned by taxi drivers. So, sometimes I just have to walk back home (25 min).