According a World Health Organization (WHO) report from last year, there are 13 Indian cities in the top 20 most polluted cities in the world.
The report by the WHO ranked 1600 cities across 91 countries according to the quality of air measured for concentrations of PM10 and PM2.5. The particles are pollutants which are used to measure air quality.
The harmful particles stick to the lungs and cause various diseases.
The city of Delhi the average is 153 ug/m3 (micrograms per cubic metre of air), which is 6 times the recommended maximum of the WHO.
Two Punjab cities ranked in the TOP 20: Amritsar and Ludhiana
This is the full list: