The air quality improved significantly but was in the "very poor" category in Ghaziabad, Noida, Greater Noida and Faridabad, while it was "poor" in Gurgaon, according to data issued by a government agency on Wednesday. Pollutants PM 2.5 and PM 10 remained prominent in the air of the five immediate neighbours of Delhi, according to the air quality index (AQI) maintained by the Central Pollution Control Board (CPCB).
According to the index, 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 average 24-hour AQI at 4 pm on Wednesday was 336 in Ghaziabad, 321 in Greater Noida, 310 in Noida, 201 in Faridabad and 207 in Gurgaon, according to CPCB's Sameer app. On Tuesday it was 436 in Ghaziabad, 434 in Greater Noida, 432 in Noida, 416 in Faridabad and 366 in Gurgaon. On Monday it was 381 in Ghaziabad, 360 in Greater Noida, 363 in Noida, 332 in Faridabad and 292 in Gurgaon.
The CPCB states that an AQI in the "very poor" category may cause respiratory illness on prolonged exposure. The AQI for each city is based on the average value of all stations there. Ghaziabad and Gurgaon have three stations while Noida, Greater Noida and Faridabad have two stations each, according to the app.