To be fair, China's moving at a MUCH faster rate to clean their air than it took the US when they were at this stage of industrialization. And they've set their air quality targets much higher than the US, which hasn't updated its air quality standards in decades.
There is a lot more technology today than back then, so it isn’t really a fair comparison. Still, it’s good that China took the problem seriously, there was some time in 2010 when they were clearly in denial (the Us embassy in Beijing crazy bad air incident that got Twitter blocked).
I was in China around that time and I don't remember the incident leading to Twitter being blocked. In fact, I think Twitter was blocked earlier than pollution incident. I do remember everyone getting pissed off that the US Embassy reading was so different than the local one: https://www.earthdata.nasa.gov/learn/sensing-our-planet/craz...
It was not completely blocked in November 2010, but was completely blocked shortly there after as far as I remember (I was in Beijing from 2007 to 2016).
China wasn’t measuring 2.5 ppm at all back then, and was rather touting improvements in 10 ppm because a tree planting effort in the gobi temporarily solved northern china’s dust storm problem. They were basically pretending that 2.5 ppm pollution didn't exist.
The US didn't have solar and wind as real alternate energy options in the 1970s or '80s. They had nuclear, but all the environmentalists hated it then.