Ulaanbaatar has the second-worst air pollution of any city in the world, according to a survey released on Monday by the World Health Organization.

The study measured the levels of airborne particles smaller than 10 micrometers, known as PM10s, in 111 cities around the world. Ulaanbaatar had an annual average PM10s density of 279 micrograms per cubic meter. The only city with a higher measured level was Ahvaz, in southwestern Iran.

WHO released the list to highlight the need to reduce outdoor air pollution, which is estimated to cause 1.34 million premature deaths a year. The organization said investments to lower pollution levels quickly pay off due to lower disease rates and, therefore, lower health care costs.

At the other end of the list are cities in Canada and the United States, which benefit from lower population density, favorable climates, and stricter air pollution regulation. Whitehorse, Canada had a yearly average of just three micrograms of PM10s per cubic meter, while Santa Fe, the capital of the U.S. state of New Mexico, measured six micrograms.

WHO also released a shorter table comparing levels of even finer dust particles, known as PM2.5s. The level of PM2.5s considered harmful is 10 micrograms per cubic meter. In this list, Ulaanbaatar ranked worst with 63.0 micrograms.