Here are the countries with the cleanest cities

The next two countries also tied for the most cities with clean air, at 5 apiece. Portugal's second biggest city is also its cleanest, in part because it isn't as industrial as other parts of the country and serves as a trade port. Like Sweden, Finland is also a partner of the Climate and Clean Air Coalition and cutting down on carbon emissions.

Portugal's cleanest city - Porto, 7 µg/m3

Finland's cleanest cities - Oulu and Jyväskylä, 6 µg/m3

Spain's cleanest cities, Arrecife and Las Palmas both are located off the coast of Morocco in the Canary Islands. The islands have clean air because of little industrialization, as tourism is one of their main economic drivers.

Spain's cleanest cities -Arrecife and Las Palmas, 6 µg/m3

New Zealand has given a lot of attention to PM10, another harmful pollutant like PM2.5 (though a bit bigger in diameter), which has helped it rack up 14 cities with relatively clean air. Its two biggest cites, Auckland and Wellington, both have low annual PM2.5 means.

New Zealand's cleanest cities - Lower Hutt, Upper Hutt and Wainuiomata, which are near one another in the southwest corner of New Zealand's northern island - 5 µg/m3

The two biggest cities in Australia also have the lowest air pollution. In fact, the five most populated cities in the country all have annual PM 2.5 means that are considered healthy by WHO, in part, because the country mandates that there can't be more than an annual PM 2.5 mean of 8 µg/m3.

Australia's cleanest cities - Melbourne, Illawarra, Geelong, Sydney, Lower Hunter, Traralgon - 5 µg/m3

Even though the world's most populated metropolitan didn't make the list, Japan's most clean cities, the 18 that did make the cut are still an impressive bunch. Japan has been a long-time leader in clean air intiatives dating back to the Kyoto Protocol of 1992, which gave the commitment of countries to cut down on greenhouse gas emissions.

Japan's cleanest cities - Chikusa-ku, Nagoya, Shimuzu-ku, Shizuoka, and Aoba-ku, Sendai - 6 µg/m3

Of the countries with the least amount of air pollution, Canada, which comes in second in number, has the cleanest of the clean. Half of the provinces and territories capitals had an annual PM 2.5 mean that's considered healthy, including Toronto, Ottawa, and Vancouver. Canada has been attentive to keeping its air clean, even having a Clean Air Day to draw attention to harmful pollutant.

And even though Canada comes second on this list, it does have the city with the least amount of air pollution: Powell River, British Columbia. Of the more than 1,600 cities monitored by the WHO, Powell River was the only one with a seriously low annual PM2.5 mean of 2 µg/m3.

The United States tops the WHO's list as the country with the most cities with clean air with a whopping 274, though to be fair, 69 of those were cities with 10 µg/m3 — right at the cutoff point. With the help of the EPA attention to PM 2.5 and clean air initiatives, this gives some hope that there are places in the states where you can get a big gulp of clean air.

US' cleanest cities - Lake Havasu City-Kingman, Arizona; Clearlake, California; Bellingham, Washington; Bremerton-Silverdale, Washington; Durango, Colorado; Dickinson, North Dakota; and Prescott, Arizona - 4 µg/m3.