those seven countries are: Australia, New Zealand, Estonia, Iceland and "some small island states". The dirty air criteria is "a yearly average of no more than

those seven countries are: Australia, New Zealand, Estonia, Iceland and "some small island states". The dirty air criteria is "a yearly average of no more than 5µg of PM2.5 per cubic metre", and while many US cities have clean air, US-a-whole apparently did not make the cut.