Furnace oil and pet-coke are the dirtiest by-products from the refinery process and use of these fuels was banned in Delhi in 1996.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/supreme-court-bans-dirty-fuel-fight-pollution-delhi
[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/oil-pollution
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/industrial-pollution
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/haryana
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/uttar-pradesh
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/diwali
[9] http://admin.indiaenvironmentportal.org.in/category/thesaurus/festival
[10] http://admin.indiaenvironmentportal.org.in/category/thesaurus/centre-science-and-environment-cse