Delhi’s air quality deteriorated to very poor category on Wednesday due to decreased wind speed that slowed dispersion of pollutants, authorities said. According to the Central Pollution Control Board (CPCB) data, the overall air quality index (AQI) in the city was 379, which falls in the ‘very poor’ category.

An AQI 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’. The city’s air quality was severe till Sunday but with improved wind speed of 20 km/hr, the air quality significantly improved and was recorded in ‘poor’ category, authorities said.

But on Wednesday, the air quality again deteriorated as the wind speed dropped. As many as 14 areas recorded ‘severe’ air quality and 17 very poor air quality, the CPCB said.

In the NCR, Ghaziabad recorded severe air quality while Faridabad, Noida, 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 at 250, while the PM10 level 400, it said.

The Centre-run System of Air Quality and Weather Forecasting (SAFAR) said the overall air quality index over Delhi was “very poor” after a short spell of “poor” days.

“Other weather conditions remain more or less same except that wind speed decreased from 5.3 kmph to 2.5 kmph. Since the speed drop is substantial, it has slowed down the dispersion significantly. The AQI will continue to remain in very poor category in next three days,” the SAFAR said.