Air purifiers are gradually coming to be seen as a weapon of choice in fighting the negative health effects of air pollution in the United States. In schools from California to Rhode Island, IQAir is working with parents, educators and government air-quality agencies to install high performance air purifiers and air filtration systems in classrooms where elevated air pollution triggers allergies, asthma, absenteeism and lowered test scores. More than half of all Americans still live in areas where pollution levels often make it dangerous to breathe, according the the American Lung Association, with whom IQAir is the exclusive educational partner for the air purifier industry. But while the air is only slowly improving in the United States, it’s getting worse elsewhere in the world.

The reality of worldwide air pollution and its effect on public health received international attention last week as the World Health Organization (WHO) released data on outdoor air pollution from almost 1,100 cities in 91 countries. The data included annual mean levels of pollution at two different particle sizes, including PM2.5 fine particle concentrations. There was not an American city in the top 25. There were, however, two American cities in the top 50 – Fresno and Bakersfield, both in the San Joaquin Valley in Southern California.

The ten worst cities in the world for breathing (based on PM2.5 annual mean levels):

1. Ulaanbaatar, Mongolia
2. Antanananrivo, Madagascar
3. Kuwait City, Kuwait
4. Mexicali, Mexico
5. Accra, Ghana
6. Zabrze, Poland
7. Dakar, Senegal
8. Krakow, Poland
9. Torino, Italy
10. Lima, Peru

Particulate air pollution in Ulaanbaatar was almost three times higher than in Bakersfield. This is a city where a high-performance air purifier should be standard in every home and classroom. “When Ulaanbaatar’s one million citizens breathe, their lungs act like air filters, catching and storing harmful dust,” a spokesperson for the World Bank says on the World Bank’s website. The air pollution in Ulaanbaatar is worst in winter, and is caused mainly by dust from unpaved roads as well as pollution from power plants, coal stoves and other sources.

As Forbes Magazine points out, the WHO report only includes data for cities that report their pollution levels. Notably absent from the WHO data on PM2.5 pollution: China. In a Time Magazine listing in 2007 of the world’s most polluted places (including air, water, radioactivity, etc.), two cities in China – Linfen and Tianying – topped the list.

Check out (Excel file) the WHO dirtiest cities database at http://www.who.int/entity/phe/health_topics/outdoorair/databases/OAP_database_8_2011.xls. To see what Ulaanbaatar looks like on a bad day, check out the photographs athttp://totobobo.com/blog/scary-pollution-in-mongolia/.