Delhi's air remained severely polluted after Diwali, with IITM data pointing to fireworks as the biggest contributor to the early-morning pollution spike. Delhi woke up to a thick blanket of smog on November 9, the day after Diwali, as its air quality remained dangerously poor.Now, an assessment by the Indian Institute of Tropical Meteorology (IITM) has pointed to the biggest contributor to the post-festival pollution spike: firecrackers.