NEW DELHI: The air quality index of the national capital plummeted to 221 and stood in the poor category on Saturday, a day after improving a notch, with West Delhi recording the most polluted air, according to Central pollution Control Board (CPCB) data. As per the CPCB, out of 35 pollution monitoring stations, the air quality index in as many as 24 stations is in the poor category, while 10 stations recorded the index in the moderate category, one was non-functional. The area near West Delhi's Mundka recorded the highest AQI at 286. The System of Air Quality Weather Forecasting and Research (SAFAR) categorizes air quality in the 0-50 range as good, 51-100 as satisfactory, 101-200 as moderate, 201-300 as poor, 301-400 as very poor and above 400 as severe. (IANS)