While PM 2.5 and PM 10 stayed above the national standards, values of SO2 (Sulphur dioxide) recorded in Delhi were within the National Ambient Air Quality Standard.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/delhi%E2%80%99s-air-quality-plunged-sharply-2016
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/indian-express-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/air-quality-standards
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/pm-25
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/rspm-pm-10
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/central-pollution-control-board-cpcb
[9] http://admin.indiaenvironmentportal.org.in/category/thesaurus/thermal-power-plants
[10] http://admin.indiaenvironmentportal.org.in/category/thesaurus/environment-pollution-control-authority-epca
[11] http://admin.indiaenvironmentportal.org.in/category/thesaurus/centre-science-and-environment-cse