Thirteen of the dirtiest 20 cities were Indian, with New Delhi, Patna, Gwalior and Raipur in the top four spots.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/indian-cities-have-dirtiest-air-delhi-top-says-who
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/indian-express-new-delhi
[3] http://admin.indiaenvironmentportal.org.in/category/thesaurus/delhi
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/patna
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/gwalior-t
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/raipur-t
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/air-pollution
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/who
[9] http://admin.indiaenvironmentportal.org.in/category/thesaurus/china
[10] http://admin.indiaenvironmentportal.org.in/category/thesaurus/pm-25