Though still in the "poor" category, air quality in Delhi significantly improved on Monday due to "unusual increase" in the wind speed, authorities said. Till Sunday, the air quality was in the "severe" category.
An Air Quality Index between 100 and 200 comes under the ''moderate'' category, 201 and 300 is considered ''poor'', 301 and 400 ''very poor'', while that between 401 and 500 ''severe''.
As many as 26 areas recorded ''poor'' air quality and four ''moderate'', the CPCB said.
In the National Capital Region (NCR), Ghaziabad, Faridabad, Noida and Greater Noida recorded ''poor'' air quality.
The overall PM2.5 level -- fine particulate matter in the air with a diameter of less than 2.5 micrometers -- in Delhi was at 109, while the PM10 level 192, it said.
"The wind speed is unusually faster for this time of the year and improving the air quality rapidly. The AQI is predicted to remain in ''poor'' category tomorrow and then to start increasing slowly from January 16 for next two days but to remain in the lower range of very poor," the SAFAR said.
Experts say humidity and cold weather conditions can work against improving air quality.