A senior CPCB official said: “The rise in air pollution can be attributed to adverse meteorological conditions -- decrease in average temperature, low wind speed, and increase in humidity -- in and around Delhi and the fact that people probably burst more smoke-producing crackers.”

This year, the CPCB conducted real-time continuous ambient noise monitoring at 35 locations in seven cities including Delhi, Mumbai, Chennai, Kolkata, Bangalore and Hyderabad.

According to the Indian Meteorological Department (IMD), visibility level the morning after Diwali was normal at 1,000 metres. “Though there was a slight smog cover which enveloped the city in the morning the air cleared up by late morning,” said a Meteorological Department official.

Delhi had faced suffocating weather conditions with the city enveloped in smog from October 27 to November 8.

Centre for Science and Environment (CSE) environmental scientist Anumita Roychoudhary said: “With pollutants dispersing two days before Diwali, the smog situation in Delhi has seen an improvement. But that doesn’t mean air pollution levels are low in the city. Several places in Delhi saw a rise in air pollution and the bursting of crackers only adds to the pollution.”

Also though Supreme Court had in 2005 put a ban on the use of firecrackers after 10 p.m. on Diwali night, “Delhi saw several people bursting crackers much after the stipulated time adding to the pressure on air quality,” added Ms. Roychoudhary.

The Delhi Government has meanwhile maintained that because of the extensive campaign, use of fire crackers has gone down. A Delhi Government environment department official said: “This year we had stricter norms to check crackers sale and only 804 retail cracker outlets were allowed in the city.”