The air quality index continued to fluctuate between the “severe” and “very poor” categories in Delhi.

The city’s 24-hour average air quality index, recorded until 4 pm on Sunday, was 318 (very poor), improving rom the severe category recorded the previous day when it was 412, according to data from the Central Pollution Control Board (CPCB).

None of the 38 monitoring stations in Delhi recorded AQI in the severe category on Sunday, compared to 20 stations that recorded severe air quality the previous day, according to the SAMEER app, which provides hourly updates on the National Air Quality Index.

An AQI between 0 and 50 is considered “good,” 51-100 “satisfactory,” 101-200 “moderate,” 201-300 “poor,” 301-400 “very poor,” 401-450 “severe,” and above 450 “severe plus.” CPCB data identified PM2.5 as the primary pollutant, with its levels recorded at 138 at 3 pm.

PM2.5 particles, measuring 2.5 micrometers or smaller (approximately the width of a human hair), pose significant health risks as they can penetrate deep into the lungs and enter the bloodstream, according to the CPCB.

The Centre’s Decision Support System (DSS) for Air Quality Management estimated that vehicular emissions contributed 18.1 per cent to Delhi’s pollution on Sunday. Stubble burning, another major factor, accounted for 19 per cent of Delhi’s pollution on Saturday.