Delhi recorded 'very poor' air quality on Saturday even as authorities predicted improvement as good wind speed will continue to disperse pollutants faster.
The air quality had slipped to "severe" category on Thursday.
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'.
On Saturday, as many as 10 areas recorded "severe" air quality and 22 "very poor", the CPCB said.
In the National Capital Region, Noida recorded "severe" air quality, while Faridabad, Ghaziabad, Gurgaon and Greater Noida recorded "very poor" air quality, it said.
The overall PM2.5 level -- fine particulate matters in the air with a diameter of less than 2.5 micrometers -- in Delhi was 267, while the PM10 level was 410, it said.
The Centre-run System of Air Quality and Weather Forecasting (SAFAR) said the overall air quality over Delhi is very poor.
"The air quality will further improve a few notch by tomorrow as good wind speed will continue to disperse pollutants faster than that of accumulation due to colder condition and fog," the SAFAR said.
It said moderate foggy conditions due to radiation fog will prevail for the next two days over Delhi and its surrounding regions and may not allow significant improvement.
An active western disturbance is very likely to cause fairly widespread moisture intrusion over the northern region including Delhi, the SAFAR said.