Delhi pollution: The air quality in Delhi reached the 'severe' zone, leading to the implementation of stage III of the Graded Response Action Plan. Primary schools in Delhi will be closed for the next two days, and older emission standard vehicles are prohibited in certain districts of the National Capital Region. The Air Quality Index (AQI) reached 402, entering the severe category for the first time this season. Stubble burning and unfavorable meteorological conditions are cited as the reasons for the sudden deterioration.