from my question.
California has a lot of air quality restrictions and has issues with smog too. Lots of people and cars will impact air quality.
China has several of the largest cities in the world. And the most cars in the world.
Also, China is doing more to address this issue than America.
https://www.scmp.com/news/china/policies-politics/article/2137666/china-has-new-three-year-plan-clean-environmentEdited by MrBlueSky at 14:56:11 on 05/14/19