The fact that Delhi's air is laden with ultrafine particulates is undisputed. But does that automatically make it "toxic"?
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/how-toxic-delhis-air-study-sheds-light
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/times-india-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/pm-25
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/rspm-pm-10
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/air-quality-standards
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/health-effects