4.2x more people though, not much point in comparing only 1 figure like that without more context.

Ah but you should also check China's population vs that of the US, that will put things in perspective. Also check if China's pollution is due to being a manufacturing hub for other countries that might outsource their own manufacturing. You might be surprised. You can't pay China to pollute for you and then blame China for polluting for you. Also, the US used to sell many ICE cars to China. The US can't blame China for polluting if the US pushes pollution sources to China. China has been electrifying to push back against those ICE cars from the US. Polluting to produce solar panels is also much cleaner overall than polluting to produce even more pollution sources.