The capital's pollution hit emergency levels on Thursday, according to the U.S. embassy.
The overall AQI Thursday was recorded in the "severe plus emergency" category at 642.
When questioned about the air quality readings, West Bengal Pollution Control Board chairman Kalyan Rudra refused to draw any conclusion about the improvement or deterioration in the air pollution during Kali Puja and Diwali on Tuesday and Wednesday respectively.
The air was hazardous at some areas with the AQI almost touching 500.
On Diwali, crackers were bursted on large scale in these cities and despite Supreme Court order on time limit, sound of crackers could be heard after 10 PM.
Also, the apex court had banned the sale of traditional crackers and allowed only "green crackers" in Delhi-NCR, but there was no clarity as to how many people could procure these, or the ones not containing the polluting barium salts.
"We have asked all police stations to follow the Supreme Court's guidelines on bursting firecrackers and to ensure action against those violating it", Mumbai Police spokesperson Manjunath Singe said.
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The US Consulate's air quality index on Thursday showed PM 2.5 count as "very unhealthy" at 211 AQL - meaning everyone may experience serious health effects.
Areas affected the most included Anand Vihar (AQI: 999), Lodhi Road (AQI: 500), Chanakyapuri (AQI 459) and the localities around Major Dhyan Chand National Stadium (AQI: 999), all under "hazardous" category.
Municipal agencies persons were seen spraying water at some areas in the city in the morning hours as a measure to clear the air and make the dust settle. There was a similar spike in air pollution levels in other major cities. It continued increasing slowly and crossed 250 (severe category) by 3 a.m.
In the absence of a national policy to tackle air pollution, Aggarwal suggests a Supreme Court-monitored committee empowered to direct across ministries and States, for a coherent approach on issues from automobiles to realty, crackers to stubble burning, besides protection of the country's green spaces - all of which affect the air we breathe.
These indices measure the concentration of tiny poisonous particulate matter.
As many as 209 calls were received by the Delhi Fire Services on Diwali, including one related to a huge fire in a factory at Bawana, officials said.
Last month the World Health Organization said exposure to toxic air indoors and out kills some 600,000 children under the age of 15 each year.