In December 2015, week-long analysis of data from #breathe devices showed Delhi's air pollution was one-and-a-half times worse than in Beijing
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/delhi-tops-most-polluted-megacity-list-says-who
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/business-standard-new-delhi
[3] http://admin.indiaenvironmentportal.org.in/category/thesaurus/delhi
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/air-pollution
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/who
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/pm-25
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/central-pollution-control-board-cpcb
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/health-effects