Delhi recorded its lowest pollution level of this year on Sunday after a spell of rain, but the air quality remained in the 'very poor' category, authorities said.
According to the Central Pollution Control Board (CPCB) data, the overall Air Quality Index (AQI) in the city was 338.
An AQI between 100 and 200 comes under 'moderate' category, 201 and 300 is considered 'poor', 301 and 400 'very poor', while that between 401 and 500 is 'severe'.
Delhi's air quality has been oscillating between upper range of 'very poor' and 'severe' category for the past two weeks.
Thirty-one areas in Delhi recorded 'very poor' air quality on Sunday, while in two areas it was 'poor', the (CPCB) data revealed.
In the National Capital Region, Ghaziabad, Faridabad, Gurgaon and Noida recorded 'very poor' air quality, it said.
According to authorities, Delhi's air quality improved significantly on Sunday after rainfall washed away pollutants.
The overall PM2.5 level (fine particulate matter in the air with a diameter of less than 2.5 micrometers) in Delhi was recorded at 184 while the PM10 (fine particulate matter in the air with a diameter of less than 10 micrometers) level was at 274, the CPCB said.
The Centre-run System of Air Quality and Weather Forecasting (SAFAR) said the overall air quality in Delhi was 'very poor'.
"The rainfall along with sufficient wind speed was enough to wash away air pollutants to an extent and improved the AQI. Air quality is likely to improve much faster during the day as moderate surface wind speed is positively working to disperse pollutants which is the key factor now in keeping pollution in check under cool and foggy weather conditions," the SAFAR said.
It, however, noted that the respite is not expected to last longer than two days as relative humidity is very high and temperature is likely to drop further which will force boundary layer to come down and will hold pollutants near the surface.
The AQI will start to increase gradually from Tuesday but will continue to remain in 'very poor' range, SAFAR said.