The air quality in Delhi kept under 'very poor' category on Friday morning because of high humidity, officials said.
The city received 8 mm rainfall till 8.30 am in past 24 hours and relative humidity was 94 per cent, a MeT department official said.
The air quality index (AQI) of Delhi was 350 at 9 AM, according to Central Pollution Control Board (CPCB).
An AQI between 201 and 300 is 'poor', 301-400 'very poor' and 401-500 'severe' while the AQI above 500 falls in the severe plus category.
After a brief relief, the national capital's air quality plunged to the "very poor" category on Thursday because of high humidity following light rain, officials said.
Delhi had been breathing relatively less polluted air for three days after a bright sun and improved wind speed pulled the city out of the grip of a dense haze that had been lingering over it since October 29.
But the increased humidity on Thursday proved harmful, they said.
Delhi's overall air quality index read 309 at 4 pm and 320 at 7 pm on Thursday.