At the other end of the list are cities in Canada and the United States, which benefit from lower population density, favorable climates and stricter air pollution regulation.

污染最轻的是美国和加拿大的城市，原因是它们的人口密度低，气候怡人，并且空气污染管理规定非常严格。

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At the other end of the list are cities in Canada and the United States, which benefit from lower population density, favorable climates and stricter air pollution regulation.

在污染排行中最靠后的是加拿大和美国的城市，受益于较低的人口密度、优越的气候和较严格的空气污染法规。

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