There are no outsiders when it comes to pollution. We get one planet. That's it.

So, China is free to choose to pollute, as is Europe and the US free to choose production from a source that doesn't pollute as much.

Their electrical infrastructure that is built on coal (60% of current generation) even if they've made huge improvements. Rare earth mining and building of all those electrical batteries and solar panels is a pretty dirty business. Reality is China produces a colossal amount of stuff, and much of it is pretty dirty (it would probably be dirty anywhere as that's the nature of making things at an industrial scale)

Right now China seems headed in the right direction for pollution, moreso than the US. And probably the only way they end up reducing pollution completely is to grow wealthy enough to replace old methods.