The average air quality was recorded in the "very poor" category in Ghaziabad, Noida and Greater Noida on Thursday, while it was "poor" in Gurgaon and Faridabad for the second consecutive day, data issued by a government agency showed.
Pollutants PM 2.5 and PM 10 also remained 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 345 in Ghaziabad, 313 in Noida, 358 in Greater Noida, 290 in Faridabad and 294 in Gurgaon, according to the CPCB''s Sameer app.
On Wednesday, it was 356 in Ghaziabad, 311 in Noida, 348 in Greater Noida, 294 in Faridabad and 247 in Gurgaon.
The CPCB states that an AQI in the "very poor" category may cause respiratory illness to people on prolonged exposure, while that in "poor" category may lead to breathing discomfort to most people on prolonged exposure.
The AQI for each city is based on the average value of all monitoring stations there. Ghaziabad, Gurgaon and Noida have four such stations while Greater Noida and Faridabad have two stations each, according to the app.
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