Delhi's air quality worsened on Thursday morning compared to Wednesday though it remained in the 'poor' zone. Air Quality Index was at 254 in ITO and 246 in Patparganj in the morning, both in 'poor' category, as per Delhi Pollution Control Committee data. Rising pollutants led to a cover of haze over the DND flyway & Mayur Vihar area. The air quality is expected to plunge to ‘very poor’ over the weekend, government agencies said. The share of stubble burning in the neighbouring states of Punjab and Haryana in PM 2.5 levels rose to 15% on Wednesday, as compared to 8% the previous day.