Last year, Delhi acquired the top slot in the list of most polluted cities in the world, followed by Beijing.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/most-polluted-ganga-valley-gets-help-scientists-15-nations
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/ndtv
[3] http://admin.indiaenvironmentportal.org.in/category/thesaurus/air-pollution
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/himalaya
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/india
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/china
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/industrial-pollution
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/indian-institute-technology-iit