Delhi is being labelled by the WHO as the most polluted city in the world.
Links:
[1] http://admin.indiaenvironmentportal.org.in/content/spot-show-delhi-worlds-most-polluted-city
[2] http://admin.indiaenvironmentportal.org.in/category/thesaurus/cars
[3] http://admin.indiaenvironmentportal.org.in/category/thesaurus/congestion
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/air-pollution
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/vehicular-pollution
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/urban-air-quality
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/health-effect
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/delhi