The air quality index in Delhi reached a high of 450 on November 3, and has been topping the 300 mark almost consistently between October 27 and November 8. On Wednesday, for the first time in 15 days, the air quality index was below 300, at 260.
While Delhi’s air quality, on which mainstream media focuses, improved slightly, smaller towns –Ambala, Khanna, Kurukshetra and Ludhiana – had severely polluted air (over 400) on November 9, according to the air quality index bulletin published by the Central Pollution Control Board.
But what does having an air quality index over 400 really mean?
For one, it means that people are breathing air that has an average concentration of 250 micrograms of PM 2.5 per cubic metre (µg/m3) in a day, according to the air quality index-to-concentration converter. PM 2.5 refers to inhalable particulate matter that can enter the bloodstream and has several health impacts. A level of 250 µg/m3 is four times the permissible amount – 60 µg/m3 over a 24-hour period – according to the standards defined by the Central Pollution Control Board.
It also means that the concentration of pollutants in the air “affects healthy people and seriously impacts those with existing diseases”.