4. Stockholm, Sweden
PM 2.5 annual mean, ug/m3: 5.51
This most populous city in Nordic countries is leading the way when it comes to air quality and very low pollution in general. One of the reasons is that Stockholm is surrounded by nature. Green surface and lakes are everywhere, and in addition to wonderful nature, its inhabitants make sure to be as eco-friendly as possible. The fact that Sweden imports garbage for recycling tells you more than enough about this country’s eco-friendliness.
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