Delhi's air quality was recorded in the "poor" category on Sunday despite an "unusual improvement" due to increased wind speed, favourable for dispersion of pollutants, authorities said.
The overall air quality index (AQI) was recorded at 232 - which falls in the 'poor' category, according to the Centre-run System of Air Quality and Weather Forecasting (SAFAR).
Three areas in the national capital recorded 'very poor' air quality, while 21 areas recorded 'poor' air quality, according to data from the Central Pollution Control Board (CPCB).
The level of PM2.5 (particles in the air with a diameter of less than 2.5 micrometres) was recorded at 111 and the PM10 level was recorded at 241, it said.
An AQI between 0 and 50 is considered 'good', 51 and 100 'satisfactory', 101 and 200 'moderate', 201 and 300 'poor', 301 and 400 'very poor', and 401 and 500 'severe'.
According to SAFAR, the improvement in air quality is unusual for this time of the year.
"The major role is being played by late-night faster wind speed. However, the air quality is expected to keep oscillating between poor and very poor for the next three days," SAFAR said.
