Skip to main content
Part of complete coverage on

Top 20 most polluted cities in the world

May 8, 2014 -- Updated 1003 GMT (1803 HKT)
STORY HIGHLIGHTS
  • Delhi is most polluted city in the world in PM2.5 concentrations
  • Half of the top 20 most polluted cities were in India, according to data
  • PM2.5 is considered most harmful to health

(CNN) -- Air quality in most cities that monitor their pollution levels exceed what the World Health Organization deems as safe.

Delhi has the highest level of the airborne particulate matter, PM2.5 considered most harmful to health, with 153 micrograms. Not far behind is another Indian city, Patna with 149 micrograms. These figures are six times what the WHO considers a "safe" limit -- which is 25 micrograms.

Half of the top 20 cities in the world with the highest levels of PM2.5 were in India, according to the pollution data released by the WHO, which included 1,600 cities. Other cities with high levels were located in Pakistan and Bangladesh.

How pollution affects weather patterns
Global air pollution on the rise
China tackles 'airpocalypse'
Chinese school builds clean air dome

PM2.5 refers to the diameter measured in microns of particulates such as ammonia, carbon, nitrates and sulfate -- which are small enough to pass into the bloodstream and cause diseases such as emphysema and cancer.

The WHO data echoes an earlier study this year which found that air pollution in New Delhi is now worse than Beijing.

No Chinese cities ranked in the top 20 most polluted cities, despite thick, gray smog filling its cities and millions of residents commuting behind surgical masks. Beijing reported 56 micrograms of PM2.5. This year, Chinese leaders have declared "war on pollution."

Beijing's emergency measures amid fog of pollution

Delhi has been described as having weak enforcement of pollution controls by India's Center for Science and Environment, a public interest group.

"Originally designed as compact entities to reduce the length of travel ... (Indian cities) are becoming victims of killer pollution, congestion ... and a crippling car-dependent infrastructure," according to the group.

And the world's most polluted city is...

Air pollution has spread by increasing reliance on fossil fuels, coal-fired power plants, cars and the use of biomass for cooking and heating.

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

ADVERTISEMENT
Part of complete coverage on
August 27, 2014 -- Updated 0023 GMT (0823 HKT)
Wilson Raj Perumal tells CNN how he rigged World Cup games: "I was giving orders to the coach."
August 27, 2014 -- Updated 2236 GMT (0636 HKT)
A 9-year-old girl learning to fire a submachine gun accidentally killed her instructor at a shooting range, according to Arizona authorities.
August 26, 2014 -- Updated 1255 GMT (2055 HKT)
ISIS has made surprise gains in Iraq and Syria in recent months, but may begin to suffer setbacks on the battlefield.
August 26, 2014 -- Updated 1844 GMT (0244 HKT)
The fear of Russian invasion is receding but peace may still be tricky to find.
August 27, 2014 -- Updated 1228 GMT (2028 HKT)
Was a police officer justified in shooting and killing Michael Brown?
August 27, 2014 -- Updated 0815 GMT (1615 HKT)
Don't like the country you live in? Meet the people who created their own "micronations."
August 27, 2014 -- Updated 2157 GMT (0557 HKT)
The signs exist that indicate U.S. airstrikes into Syria are on the way.
August 27, 2014 -- Updated 1649 GMT (0049 HKT)
The mother of a hostage freed after two years captivity says it's not time to party.
August 26, 2014 -- Updated 0946 GMT (1746 HKT)
We asked you what you would like to know about Ebola. Experts answer some of your most common questions and concerns.
CNN joins the fight to end modern-day slavery by shining a spotlight on its horrors and highlighting success stories.
Browse through images from CNN teams around the world that you don't always see on news reports.
August 26, 2014 -- Updated 0600 GMT (1400 HKT)
"I just love it when I get milk-to-dark converts," says Kerrin Rousset, before she leads a small cocoa-hungry crowd through Zurich's Old Town.
ADVERTISEMENT