The air quality in China is lot better now than a decade ago. The smog was so bad in 2012 and I remembered the AQI hitting 999 (the max it would go) on more than one occasions during Beijing winter.

Went back again in early 2024 and it was so much better, pollution still noticeable on more days than not but at least half the time I spent had AQI below 100.

I was in Shenzhen in 2017 and again recently. The difference is huge. The air quality walking around the street is very good and you never smell gasoline.