The first stage, GRAP-1, kicks in when the AQI is between 201 and 300; the second stage, GRAP-2, is invoked when the AQI is between 301 and 400; GRAP-3 kicks in between 401 and 500; and GRAP-4 is invoked when the AQI is more than 450.
http://dlvr.it/TVjFgG