In a ranking released by the World Health Organization (WHO) this week, Estonia topped the list as the country with the best overall air quality. Mauritius was second and Canada and Australia tied for third place. The survey ranked 1,100 cities in 91 countries. Iran and Mongolia scored worst, though those ranking should be taken with caution because some countries have a several cities with monitoring stations (Canada) while Ulaanbaatar is the only city measured in Mongolia. In general, cities in Iran, India, and Pakistan were among the worst on the planet for air pollution, whereas cities in Canada and the United States fared better because they benefit from lower population density, favorable climates and stricter air pollution regulation.
The WHO measured the levels of airborne particles smaller than 10 micrometers, called PM10s. In North America, Whitehorse, Canada had a yearly average of just 3 micrograms of PM10s per cubic meter, while Santa Fe, USA measured 6 micrograms. For comparison, Washington, D.C. came in at 8 micrograms, Tokyo measured 23 micrograms, and Paris had 38 micrograms of PM10s per cubic meter.
The WHO said investments to lower pollution levels quickly pay off due to lower disease rates and health-care costs.