NEW DELHI: The air quality in Delhi kept under a 'very poor' category on Friday morning because of high humidity, officials said.

The city received 8 mm rainfall till 8.30 am in the past 24 hours and relative humidity was 94 percent, a MeT department official said. The air quality index (AQI) of Delhi was 350 at 9 AM, according to the 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 a 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.