Every year, in September-November, farmers in India's northern Punjab and Haryana states burn off the crop straw and stubble in preparation for the sowing season. After harvesting rice, farmers get a short window to plant winter crops such as wheat and rapeseed and late sowing means lower yields.
The cost of disposing of the crop residue is high which makes them opt for stubble burning instead.
The fields were filled with huge amount of smoke as farmers burnt stubble despite efforts by authorities to convince them to not burn crop residue.
The smoke from fields combines with urban pollution from industrial emissions and vehicle exhaust and brings a sharp spike in pollution. Every winter, a thick blanket of smog settles over northern India, including the capital New Delhi, shutting schools and banning construction.