GRAP -- a set of anti-air pollution measures followed in the Delhi-NCR region in the winter season -- classifies actions under four different categories - Stage I - 'Poor' (AQI 201-300), Stage II - 'Very Poor' (AQI 301-400), Stage III - 'Severe' (AQI 401-450), and Stage IV - 'Severe Plus' (AQI >450).