The average air quality deteriorated to reach "very poor" category in Ghaziabad and Greater Noida, and "poor" in Noida, Gurgaon and Faridabad, according to data issued by a government agency on Tuesday.
Pollutants PM 2.5 and PM 10 also remained high 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 Tuesday was 334 in Ghaziabad, 339 in Greater Noida, 293 in Noida, 277 in Faridabad and 272 in Gurgaon, according to CPCB's Sameer app.
On Monday, it was 230 in Ghaziabad, 196 in Greater Noida, 192 in Noida, 174 in Faridabad and 204 in Gurgaon.
The CPCB states that an AQI in "poor" category may lead to breathing discomfort to most people on prolonged exposure, while "very poor" may cause respiratory illness 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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