New Delhi, Dec 19 (IANS): Delhi's air quality index (AQI) has deteriorated to the "very poor" quality with a reading of 340 on Thursday due to decrease in wind speed.

According to Safar India forecast, the overall Delhi AQI was in the "very poor" category on Thursday. A decrease in wind speed is forecast for Thursday and Friday.

The SAFAR model suggests that the AQI is likely to deteriorate sharply towards the higher end of very poor category by Friday. Some of the top hot spot regions like Adarsh Nagar, Rohini, Okhla and Vasundhara may slip into severe category but not for a prolonged period.

On December 21, wind speeds are forecast to pick up and AQI is likely to stay at middle to higher end of the very poor category. By December 22, AQI is forecast to improve to lower end of very poor category.

With the winter setting in, a decrease in minimum temperature is forecast, and conditions are favourable for fog formation in the calm early morning period, according to Safar India.