Seattle's air pollution quality is so low because there's a vast ocean separating the Seattleites from the manufacturing that supplies it with new phones, appliances, furniture, clothing, building materials and just about everything from the source of the pollution.

Rain is nice, but that has very little to do with it.

The growth in moat of these countries is up so much they cant burn enough coal to keep from brown outs.

Outsourced pollution.

If you need data, just peak at a global air pollution map. Dive into the historical metrics.