Whatever the causes of the smog, by one ranking Delhi was not just the most polluted city in the world, but “nearly five times as bad as the second most polluted city, Dhaka,” in Bangladesh next door, as Shashi Tharoor, a leader of the opposition in Parliament and best-selling author, posted on X.

The AQI in Delhi-NCR is in the ‘severe plus’ category. AQI between 0-50 is considered “good”, 51-100 is “satisfactory”, 101-200 is “moderate”, 201-300 is “poor”, 301-400 is “very poor”, 401-500 is “severe” and above 500 is a “severe plus”.

Residents in India's northern states woke up to another day of poor air quality on Tuesday, as a layer of dense fog shrouded most of the region, and pollution in the capital Delhi remained severe.