Photographs: Suzanne Plunkett/Reuters
While pollution is a major problem in almost all cities, some are more polluted than others. According to United States's Environmental Protection Agency's air-quality index, one Indian city tops when it comes to pollution.
Let's take a look at some of the most polluted cities in the world's biggest economies.
Source: The Economist
NOTE: Environmental Protection Agency's air-quality index measures PM 2.5 (particulate matter of 2.5 microns across or less per cubic metre). Such particles are small enough to be inhaled and can damage lungs. The AQI range ends at 500. A reading above 100 is deemed "unhealthy for sensitive groups" and anything above 400 is rated "hazardous" for all, according to The Economist.
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Indian city most polluted in the world
Photographs: Source: Soman/Wikipedia Commons
Ludhiana
Country: India
Particulate matter with diameter of 10 microns or less per cubic metre: 251
Global rank: 1
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Indian city most polluted in the world
Photographs: Source: Chen Zhao/Wikipedia Commons
Lanzhou
Country: China
Particulate matter with diameter of 10 microns or less per cubic metre: 150
Global rank: 2
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Indian city most polluted in the world
Photographs: Source: Thelmadatter/Wikipedia Commons
Mexicali
Country: Mexico
Particulate matter with diameter of 10 microns or less per cubic metre: 139
Global rank: 3
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Indian city most polluted in the world
Photographs: Source: Kenrick95/Wikipedia Commons
Medan
Country: Indonesia
Particulate matter with diameter of 10 microns or less per cubic metre: 112
Global rank: 4
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Indian city most polluted in the world
Photographs: Source: Hyungyong Kim/Wikipedia Commons
Anyang
Country: South Korea
Particulate matter with diameter of 10 microns or less per cubic metre: 68
Global rank: 5
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Indian city most polluted in the world
Photographs: Source: byseaninjapan/Wikipedia Commons
Busan
Country: South Korea
Particulate matter with diameter of 10 microns or less per cubic metre: 68
Global rank: 6
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Indian city most polluted in the world
Photographs: Euroluftbild.de Euroluftbild.de/Reuters
Johannesburg
Country: South Africa
Particulate matter with diameter of 10 microns or less per cubic metre: 64
Global rank: 7
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Indian city most polluted in the world
Photographs: Bruno Domingos/Reuters
Rio de Janeiro
Country: Brazil
Particulate matter with diameter of 10 microns or less per cubic metre: 62
Global rank: 8
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Indian city most polluted in the world
Photographs: Alessandro Garofalo/Reuters
Turin
Country: Italy
Particulate matter with diameter of 10 microns or less per cubic metre: 46
Global rank: 9
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Indian city most polluted in the world
Photographs: Marcelo del Pozo/Reuters
Seville
Country: Spain
Particulate matter with diameter of 10 microns or less per cubic metre: 44
Global rank: 10
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Indian city most polluted in the world
Photographs: Source: Wikipedia Commons
Zaragoza
Country: Spain
Particulate matter with diameter of 10 microns or less per cubic metre: 44
Global rank: 11
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Indian city most polluted in the world
Photographs: Charles Platiau/Reuters
Paris
Country: France
Particulate matter with diameter of 10 microns or less per cubic metre: 38
Global rank: 12
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Indian city most polluted in the world
Photographs: Source: Bobak Ha'Eri/Wikipedia Commons
Bakersfield, California
Country: The United States
Particulate matter with diameter of 10 microns or less per cubic metre: 38
Global rank: 13
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Indian city most polluted in the world
Photographs: Jumana El-Heloueh/Reuters
Montreal
Country: Canada
Particulate matter with diameter of 10 microns or less per cubic metre: 36
Global rank: 14
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Indian city most polluted in the world
Photographs: Denis Sinyakov/Reuters
Moscow
Country: Russia
Particulate matter with diameter of 10 microns or less per cubic metre: 35
Global rank: 15
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Indian city most polluted in the world
Photographs: Tobias Schwarz/Reuters
Dresden
Country: Germany
Particulate matter with diameter of 10 microns or less per cubic metre: 34
Global rank: 16
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Indian city most polluted in the world
Photographs: Paul Hackett/Reuters
London
Country: The United Kingdom
Particulate matter with diameter of 10 microns or less per cubic metre: 33
Global rank: 17
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Indian city most polluted in the world
Photographs: Issei Kato/Reuters
Osaka
Country: Japan
Particulate matter with diameter of 10 microns or less per cubic metre: 25
Global rank: 18
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Indian city most polluted in the world
Photographs: Mick Tsikas/Reuters
Brisbane
Country: Australia
Particulate matter with diameter of 10 microns or less per cubic metre: 18
Global rank: 19
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