CSE says that a sudden increase in air pollution after April 22 was because of the burning of farm refuse, which started in the rural parts of Punjab and Haryana from April 19
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/farm-fires-punjab-haryana-hurt-odd-even-scheme-says-cse
[2] http://admin.indiaenvironmentportal.org.in/category/author/subhayan-chakraborty
[3] http://admin.indiaenvironmentportal.org.in/category/newspaper/business-standard-new-delhi
[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/odd-even-numbered-cars
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/haryana
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/punjab
[9] http://admin.indiaenvironmentportal.org.in/category/thesaurus/centre-science-and-environment-cse
[10] http://admin.indiaenvironmentportal.org.in/category/thesaurus/vehicular-pollution