The World Health Organization has ranked Canada's air quality the third-best in the world (tied with Australia). Despite high marks for the country, the ratings given to the 70 Canadian cities included in the assessment vary greatly. Whitehorse's air contained three micrograms of particulate matter ("a complex mixture of solid and liquid particles of organic and inorganic substances") per cubic metre of air — but Sarnia, Ont., clocked in above WHO's recommended maximum of 20 micrograms per cubic metre. Use the drop-down menus to the right of the map to see which cities fall into various air quality ranges, or to select a specific city. Select the "By country" tab to see the annual average micrograms per cubic metre in 90 countries.
Source: World Health Organization
By Michael Pereira and Kerry Wall