An AQI between 100 to 200 comes under 'moderate' category, 201 and 300 is considered 'poor', 301 and 400 'very poor' while between 401 and 500 'severe'.
According to the Centre-run System of Air Quality and Weather Forecasting (SAFAR), the overall air quality of Delhi may improve due to increased wind speed.
"It may improve as wind speed is sufficiently high. Wind speed continued to remain a key factor to improve the air quality after rain washed away pollutants on Thursday. However, other factors are still unfavourable as relative humidity is high," it said.
The overall PM2.5 (fine particulate matter in the air with a diameter of less than 2.5 micrometre) level was recorded at 143 and the PM10 (fine particulate matter in the air with a diameter of less than 10 micrometre) level at 253, SAFAR said.
The national capital recorded its best air quality in moderate category in over two months on Thursday after rains washed away pollutants before slipping into the 'poor' category on Friday.
On Sunday, 18 places recorded 'very poor' air quality and 12 places recorded poor air quality, the CPCB said.
Neighbouring Ghaziabad and Greater Noida recorded 'very poor' air quality while in Noida and Faridabad it was in the 'poor catgory' and in Grurgaon it was 'moderate', the CPCB said.