An AQI between zero and 50 is considered 'good', 51 and 100 'satisfactory', 101 and 200 'moderate', 201 and 300 'poor', 301 and 400 'very poor', and 401 and 500 'severe'. The city's air quality deteriorated to the 'very poor' category on Saturday due to slow wind speed at night and a dip in the temperatures. The air quality is expected to remain 'very poor' for a few more days, according to the Centre's Air Quality Early Warning System for Delhi.
