According to the WHO's database containing results of outdoor air pollution monitoring from almost 1,600 cities in 91 countries, this list presents the 10 cities with the highest PM2.5 level in the world.

PM 2.5 refers to fine particles of less than 2.5 micrometres in diameter linked with increased rates of chronic bronchitis, lung cancer and heart disease, which are dangerous for human health.

The air quality in most cities that monitor their pollution levels exceeds what the World Health Organization deems as safe. Over half of the top 10 cities were in India. No Chinese cities ranked in the top 10 most polluted cities, despite their thick, gray smog.

The cities with the lowest level of pollution were located in Canada, the United States, Finland, Iceland and Sweden.

  Lucknow

PM 2.5 level: 96

Country: India