Stubble burning in Punjab and Haryana is a major cause of air pollution not only in the two states but also in the national capital.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/farmers-punjab-haryana-defy-ban-stubble-burning
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/ndtv
[3] http://admin.indiaenvironmentportal.org.in/category/thesaurus/punjab
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/air-pollution
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/agriculture
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/crops
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/farmers