Delhi's air quality typically worsens in winter, due to pollution from the burning of rice stubble, diesel engines, coal-fired power plants and industrial emissions. However, reports have claimed that Delhi is not the most polluted city in the country.
Pollution in the Indian capital, New Delhi, rose to a "severe" level on Thursday after revellers let off fireworks long into the night to mark the Hindu festival of Diwali.
The Delhi Traffic Police said heavy and medium goods vehicles, except those carrying essential goods, will not be allowed to enter Delhi from 11 pm on November 8.
Partly as a result of smoke from the firecrackers, the overall AQI in Delhi jumped to 642 which falls in the "severe-plus emergency" category, according to the data by SAFAR. Any reading between 301 and 400 is "very poor" and can cause "respiratory illness on prolonged exposure".
On Friday, levels of particulates 2.5 micrometers or less in diameter, the most harmful to human health, peaked at 845, according to the U.S. embassy website that monitors air quality independently.
The deterioration in air quality is being witnessed despite the Supreme Court directing that only green firecrackers be lit and that too for two hours between 8 pm and 10 pm on Diwali.
While other cities across north India recorded AQI scores of between 300 and 350, the air was significantly better in central and southern cities - with with the air in Thiruvananthapuram, Kerala, deemed "satisfactory" with a AQI score of only 64. This air will seriously affect those with ailments, according to the advisory issued by SAFAR. In case of a violation, the station house officer of the police station concerned would be held personally liable and it would amount to committing contempt of the court, the court had said.