The most polluted cities in the world are now known. Asia dominates the list – Executive Summary

A group of Swiss scientists revealed a list of the most polluted cities in the world, where their residents are most at risk of inhaling toxic particles. The Vietnamese capital, Hanoi, tops the list of 100 cities, and is the only city in which the level of air pollution is described as “extremely unhealthy.”

In this densely populated city, levels of key pollutants linked to heart disease, asthma and even cancer are 40 times higher than recommended guidelines. Other cities in the top 20 include Istanbul in Turkey, Delhi in India, Beijing and Wuhan, both in China, and Dubai in the United Arab Emirates. Only two British cities are on the list – Birmingham, which is 57th, and London, which is 89th. The rankings are provided by IQAir, a Swiss air quality technology company specializing in protection against air pollutants. It is based on data from thousands of air quality monitoring stations and air quality sensors operated by government agencies, research institutions and others. “Immediately, the classification is able to highlight the impact of events such as wildfires, biomass burning, industrial activity, sandstorms and reflective meteorological events on a city’s air quality,” IQAir said in a statement.

According to the company, Hanoi suffers from a pollutant known as PM2.5 – small particles or droplets with a diameter of less than 2.5 micrometers that are invisible to the naked eye and are inhaled without realizing it.

Scientific research suggests that the Daily Mail has shown that these tiny cancer-causing particles are small enough to enter the bloodstream through the lungs. IQAir said the PM2.5 concentration in Hanoi is 41.8 times higher than the annual air quality guideline set by the World Health Organization. But other serious air pollution in the city includes nitrogen dioxide (NO2), a reactive gas formed by automobile emissions that irritates the respiratory system. Outdoors, nitrogen dioxide contributes to the formation of ozone (O3), the main component in smog, which is also linked to health problems such as chest pain, bronchitis and asthma. In recent years, Hanoi has repeatedly featured among the world's most polluted cities, partly due to large-scale construction and emissions caused by the huge number of motorcycles and cars that cross the capital every day. Carbon emissions from northern coal plants and agricultural burning exacerbate the problem. “I had to wear a mask whenever I went out in the past few days because the air quality was so bad,” says Nguyen Minh Huong, an office employee.

“It's hard to breathe. I'm sneezing all the time, so I've had to limit my time outside.”

In total, 19 of the 20 most polluted cities are in Asia (Mexico City is the exception), which experts describe as “not surprising.” “Unfortunately, this is quite predictable and is supported by a wealth of evidence such as surface measurements, satellite data and models,” said Philip Steer, professor of atmospheric physics at the University of Oxford.

See the list of the most polluted cities in the world:

1. Hanoi Vietnam
2. Tehran, Iran
3. Bishkek, Kyrgyzstan
4. Calcutta, India
5. Dhaka, Bangladesh
6. Yangon, Myanmar
7. Karachi Pakistan
8. Tashkent, Uzbekistan
9. Beijing, China
10. Wuhan, China