Delhi is among the 13 cities in India that follows the Bharat Stage (BS) IV emission norms, while smaller cities implement BS III norms.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/early-morning-when-pollution-spikes-capital
[2] http://admin.indiaenvironmentportal.org.in/category/author/aniruddha-ghosal
[3] http://admin.indiaenvironmentportal.org.in/category/newspaper/indian-express-new-delhi
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/delhi
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/air-pollution
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/vehicular-pollution
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/cse
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/petrol
[9] http://admin.indiaenvironmentportal.org.in/category/thesaurus/diesel
[10] http://admin.indiaenvironmentportal.org.in/category/thesaurus/who
[11] http://admin.indiaenvironmentportal.org.in/category/thesaurus/health-effects
[12] http://admin.indiaenvironmentportal.org.in/category/thesaurus/vehicle-technology-and-fuel