I went in China some month ago, and in many big cities pollution, due to CO2 (and other chemical substances), is really unbearable.
I doubt you were able to notice a difference between the co2 level in China and the the level in your own home. The difference is incredibly small only about 200 parts per million.
The fine particle pollution on the other hand is very noticable. It is important to not confuse one with the other.
A co-worker was born there and moved here as a child in the 90s. She went back to her parent's village a year ago and was aghast at the pollution.
It sounded like all the vile stuff we got rid of years ago, soot, particulate, etc.
And not just the air, industrial waste, sewage, etc was all dumped in the rivers.