Last week, the World Health Organisation reported that an estimated 8.2 million deaths a year are linked to air pollution. And that number is on the rise. The most harmful pollutant to human health is called PM 2.5, short for particle matter that's less than 2.5 microns in diameter. It's found in soot, smoke, and dust, and lodges in the lungs causing long-term health problems like asthma and chronic lung disease.
PM 2.5 starts to become a health problem when there is more than 35.5 micrograms of PM 2.5 per cubic metre (written like 35.5 µg/m3) of air, according to the Environmental Protection Agency. But WHO recommends that PM 2.5 shouldn't even exceed 10 µg/m3. The most polluted cities on Earth have anywhere from nine to 15 times that amount - based on information from the WHO - and you might be surprised which make the top 10 list. Check them out:
10. Lucknow, India - 96 µg/m3 of PM 2.5
Fayaz Kabli/Reuters
Lucknow, a city in northern India, starts off the top 10 cities with the worst air pollution levels list. It still significantly has a high average air pollution level that falls into the "unhealthy" category. Vehicle emissions are a major factor in Lucknow's air pollution problem.
9. Ahmedabad, India - 100 µg/m3 of PM 2.5
Amit Dave/Reuters
India's western city Ahmedabad gets its air pollution in part from the major construction happening in the city.
8. Khorramabad, Iran - 102 µg/m3 of PM 2.5
Morteza Nikoubazl/Reuters
Khorramabad, a city in western Iran, had the country's highest air pollution levels. One of the most populous cities in Iran, Khorramabad is an agriculture hub, which likely contributes to its air pollution problems.
7. Rawalpindi, Pakistan - 107 µg/m3 of PM 2.5
Getty Images
Rawalpindi, the twin city of Pakistan's capital Islamabad, has a high average air pollution because of its heavy use of private vehicles. Rawalpindi just launched a mass transportation system in 2015, so maybe that will knock it off the top 10 list in the not-too-distant future.
6. Peshawar, Pakistan - 111 µg/m3 of PM 2.5
Fayaz Aziz/Reuters
With a population of 3.5 million people, Peshawar joins the list because of the usual suspects (vehicle and industrial emissions), as well as brick kiln emissions from the brick-making industry in the city.
5. Karachi, Pakistan - 117 µg/m3 of PM 2.5
Zahid Hussein/Reuters
Vehicle and industrial emissions combined with rapid urbanisation put Karachi as the city in Pakistan with the most air pollution.
4. Raipur, India - 134 µg/m3 of PM 2.5
Amit Dave/Reuters
Raipur, a city in central India, is the fourth most polluted Indian city in terms of average PM 2.5 levels. The reason for the high pollution is coal-powered plants and aluminum and steel production.
3. Gwalior, India - 144 µg/m3 of PM 2.5
Flickr/Prashant Ram
Of the top 20 most polluted cities, 13 were in India - including Gwalior. The Times of India attributes Gwalior's bad air pollution to coal-powered plants, cars, and inefficient energy use in buildings.
2. Patna, India - 149 µg/m3 of PM 2.5
Krishna Murari Kishan/Reuters
Patna, the second largest city in eastern India, is a major agricultural trade centre, and suffers from high pollution in part because of transportation, power generation and other industries. Its PM 2.5 levels are considered "unhealthy".
1. Delhi, India - 153 µg/m3 of PM 2.5
Rupak De Chowdhuri/Reuters
Delhi is the only one on the WHO's list that qualifies as a "very unhealthy" average PM 2.5 level. Its high pollution level is due to motor vehicles and nearby factories. To put these level into perspective, Beijing's average PM 2.5 is 56, though other calculations put it much higher.
REUTERS/Kim Kyung-Hoon
Source: Washington Post
And New York's average PM 2.5 level is a relatively healthy 14.
REUTERS/Adrees Latif
This article was originally published by Business Insider.
More from Business Insider: