Air quality plunged to "severe" levels in Ghaziabad, Noida, Greater Noida and Faridabad, while it was "very poor" in Gurgaon, according to a 24-hour data issued by a government agency on Thursday.
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 Thursday was 429 in Ghaziabad, 410 in Greater Noida, 412 in Noida, 447 in Faridabad and 364 in Gurgaon, according to CPCB's Sameer app.
On Wednesday, it was 388 in Ghaziabad, 398 in Greater Noida, 348 in Noida, 367 in Faridabad and 276 in Gurgaon.
On Tuesday, it was 324 in Ghaziabad, 312 in Greater Noida, 278 in Noida, 260 in Faridabad and 213 in Gurgaon.
The CPCB states that an AQI in the "severe" category affects healthy people and seriously impacts those with existing diseases, while "very poor" 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 such stations, while Noida, Greater Noida and Faridabad have two stations each, according to the app.
