It is said the pollution from burning paddy straw is a factor in Delhi's poor air quality.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/punjab-needs-law-awareness-contain-air-pollution-caused-paddy-straw-burning
[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/punjab
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/agriculture
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/haryana
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/air-quality-standards
[9] http://admin.indiaenvironmentportal.org.in/category/thesaurus/air-act-1981
[10] http://admin.indiaenvironmentportal.org.in/category/thesaurus/state-pollution-control-board-spcb-0