Delhi's air quality remained in the 'very poor' category this morning. The air quality index, AQI was 331 at 10.37 A.M. The Government air quality monitoring service, SAFAR said, the city's air quality was expected to turn 'severe' by tomorrow.<br />''<br />''The average AQI stood at 321 on Sunday. Yesterday, most of the 37 Air Quality Monitoring Stations in Delhi recorded air quality in the 'very poor' category.<br />''<br />''An AQI between 0 to 50 is considered 'good', 201 to 300 'poor', 301 to 400 'very poor' and 401 to 500 'severe'.<br />''<br />''Above 500 falls in the 'severe plus' category.<br />''<br />''With the winter setting in, a dip in the minimum temperature is making the air cold and heavy leading to accumulation of pollutants close to the ground.<br />