Here are the countries with the cleanest cities

Air pollution is a big problem — it’s responsible for an estimated 3.3 million deaths every year.

A tiny pollutant called PM2.5, or particulate matter smaller than 2.5 microns across, is considered the most harmful pollutant. It’s found in soot, smoke, and dust. When it lodges in the lungs, it can cause long-term health problems like asthma and chronic lung disease.

While we typically tend to focus on the places that are the least healthy, here’s a list of the most healthy.

Countries are ranked according to their number of clean cities, using data from the WHO.

4. Australia: 15 cities

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Sydney, Australia

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

2. Canada: 115 cities

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Toronto, Canada, which has an annual mean of 8 µg/m3 PM 2.5.

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.

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