As Air Quality Worsens, Delhi Pollution Control Board Stops Airing 24-hour Average

While six DPCC monitoring stations have been giving updates every 10 minutes, the average of every 24-hour cycle is no longer in public domain.

Shukla says she has been asking DPCC scientists for the averages but to no avail.

Sources also attributed this secrecy to the fact that pollution levels were very high this time in Delhi, “leading to an upswing in the number of people suffering respiratory illnesses”. They said that this was a tactic the CPCB too has been known to deploy.

"Last night, levels hit the severe category, which is the worst. You could see and sense how the visibility had come down and there was a choking haze all around," said Anumita Roychowdhury at the CSE.

Levels of PM 2.5, tiny particulate matter that reaches deep into the lungs, more than doubled within a few hours to 750 micrograms per cubic meter in the city's worst affected parts, the CPCC said.

That is 30 times a mean guideline of 25 micrograms per cubic meter on average over a 24-hour period set by the World Health Organization (WHO), which says outdoor air pollution killed 3.7 million people worldwide in 2012.