Europe has a population density of about 400 people per square kilometre. If you have a fireplace it needs to burn smokeless fuel.
The US is at 40 people per square km. It can get away with more air pollution.
Australia is at 4 people per square km. It's also one of the most urbanised countries in the world, but bush-fire smoke - most of it from hazard reduction burns carried out outside the bush-fire season - is the major source of air-pollution.