>>1019257China has issues with particulates and NOx AFAIK.
Traveled there a while ago for work and definitely wouldn't want to be there any longer than needed. I'm not sure what the west/mountainous regions are like, but the smog in Beijing was so bad that walking around the airport felt like you were in a habitation pod on some uninhabitable planet from scifi. You could stare directly at the sun without problems most days due to the smog and it was like in every city I saw and the trains between.
China is an environmental disaster and it seems like they are only now beginning to take some steps to improve air quality.