The air quality was in the "very poor" category in Ghaziabad, while it remained in the "poor" zone in Noida, Greater Noida, Gurgaon and Faridabad in the national capital region, according to data issued by a government agency on Friday.
Presence of pollutant PM 2.5 and PM 10 also remained high in 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 Friday was 304 in Ghaziabad, 297 in Greater Noida, 288 in Noida, 214 in Faridabad and 224 in Gurgaon, according to CPCB's Sameer app.
The CPCB states that an AQI in the "very poor" category may cause respiratory illness on prolonged exposure while air quality in the "poor" zone may lead to breathing discomfort to people.
The average AQI on Thursday was 277 in Ghaziabad, 283 in Greater Noida, 267 in Noida, 213 in Faridabad and 241 in Gurgaon. On Wednesday it was 319 in Ghaziabad, 331 in Greater Noida, 280 in Noida, 222 in Faridabad and 221 in Gurgaon.
The AQI for each city is based on the average value of all stations there. Noida, Faridabad, Ghaziabad have four stations each, while Gurgaon has three and Greater Noida two, according to the app.
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