When Americans picture the steel mills of Pittsburgh or industrial parts of New Jersey, images of white and grey plumes of smoke come to mind. But no matter how bad the smog can get in a U.S. city, it’s still far better than the most polluted cities in the world.

About 7 million people worldwide die from causes that can be attributed to air pollution, according to the World Health Organization. The most harmful air pollutant is PM2.5 — shorthand for particulate matter that is 2.5 micrometers in diameter or smaller. (For perspective, the diameter of a human hair is 50 to 70 micrometers, so particles that are 2.5 micrometers or smaller are very fine and inhalable.) These tiny particles make it into the bloodstream through the lungs. 

To identify the world’s most polluted cities, 24/7 Tempo reviewed the average annual concentration of PM2.5 particles in more than 2,600 cities around the globe from the World Health Organization’s 2018 update to its Global Ambient Air Quality Database. The 30 cities on this list all have a PM2.5 concentration of at least 84 micrograms per cubic meter or more. 

We also included PM10 pollution, or concentration levels of larger inhalable particles that are 10 micrometer in diameter or smaller. While the finer PM2.5 particles can get deep into the lungs and even the bloodstream, the coarser PM10 particles are less harmful, although they can irritate a person’s eyes, nose, and throat.

Click here to see the 30 most polluted cities in the world.
Click here for our detailed findings and methodology.