India, Oct. 21 -- Delhi's air quality deteriorated on Tuesday morning after a large number of people in the national capital region or NCR celebrated Diwali with firecrackers on Monday night. Thirty-four out of 37 monitoring stations recorded pollution levels in the 'red zone', indicating 'very poor' to 'severe' air quality across the national capital.

At 6:05 am on Tuesday, the city's overall Air Quality Index (AQI) stood at 347, falling in the 'very poor' category. Notably, Delhi's 24-hour average AQI, which is reported and published by the Central Pollution Control Board (CPCB) at 4pm every day, stood at 345, which also falls in the 'very poor' category.

The CPCB categorises AQI between 0 and 50 as 'good', 51 and 100 'satisfactory', ...