Faridabad, Noida, Ghaziabad, Lucknow, Gurugram, and Patna recorded "severe" air pollution with AQIs hovering well above 400 on Thursday night.
According to a report published by a research group Urban Emissions, as much as 5 million kilograms of firecrackers were burnt in the region leading to an emission of 150,000 kilograms of Particulate Matter (PM) 2.5 despite the Supreme Court's order stating that bursting of firecrackers will only be allowed from 8 pm to 10 pm on Diwali.
After the Diwali festival, levels of airborne PM 10 and PM 2.5 touched 470 and 322 respectively, up from 438 and 180 in 2018, the Central Pollution Control Board said in a bulletin.
The air quality in Delhi continues to be adverse.
Although Punjab's air quality went from "moderate" on Diwali day to "poor" by night, it has shown an improvement compared to Diwali night past year when it was reported under "very poor" category.
Giving a break up of different areas, the CPCB said in Pritampura, the PM10 and PM2.5 levels was 831 and 990 respectively this year, while last year the PM10 and PM2.5 was recorded at 677 and 690 respectively. New Delhi topped the chart with air quality index (AQI) recorded at 420.
In 2017, official data showed the PM10 level reached 595 µgm-3 and PM2.5 was 407 µgm-3.
The "hazardous" figure is roughly 33 times the World Health Organization safe limit of 25 and health experts advise people to stay indoors or use masks for protection.
On Thursday, the Supreme Court-appointed Environment Protection Authority said it was closely monitoring the situation and if the pollution shows an increasing trend then emergency measures will be imposed in the national capital.
The Supreme Court has allowed people to burst firecrackers from 8pm to 10pm only on Diwali and other festivals.
The SAFAR had warned that even if partial toxic firecrackers as compared to previous year were burnt, then the air quality would fall in the "severe" category.
The court had asked police to ensure that banned fireworks were not sold and said in case of any violation the commanding officer of the police station concerned would be held personally liable and it would amount to committing contempt of the court.
However, violations were reported from across Delhi, including areas like Anand Vihar, ITO, Jahangirpuri Mayur Vihar Extension, Lajpat Nagar, Lutyens Delhi, IP Extension and Dwarka.