EPCA observed that stubble burning in Punjab, Haryana is a contributory factor but not the only problem during winter.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/ban-diesel-vehicles-close-thermal-power-plants-epac-delhi-govt-air-pollution
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/asian-age-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/vehicular-pollution
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/heavy-duty-vehicle
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/environment-pollution-control-authority-epca
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/crops
[9] http://admin.indiaenvironmentportal.org.in/category/thesaurus/air-quality-index-aqi
[10] http://admin.indiaenvironmentportal.org.in/category/thesaurus/central-pollution-control-board-cpcb
[11] http://admin.indiaenvironmentportal.org.in/category/thesaurus/air-pollution-control