The air quality deteriorated slightly but stayed in "very poor" category in Noida, Greater Noida, Ghaziabad, Faridabad and Gurugram in the National Capital Region (NCR) on Friday, according to a government agency.
However, the concentration of major air pollutants PM 2.5 and PM 10 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 382 in Ghaziabad, 337 in Noida, 336 in Greater Noida, 324 in Gurugram and 319 in Faridabad, according to the CPCB's Sameer app.
On Thursday it was 328 in Ghaziabad, 327 in Greater Noida, 305 in Noida, 304 in Faridabad and 293 in Gurugram.
PM 2.5 and PM 10 were the prominent pollutants in Noida, Greater Noida, Ghaziabad, Faridabad and Gurugram, according to CPCB.
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 most people on prolonged exposure.
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 has two, according to the app.
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