The average air quality in Ghaziabad, Noida, Greater Noida, Faridabad and Gurgaon was in the very poor category, which upon prolonged exposure may cause respiratory illness among people, according to data issued by a government agency on Monday.
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).
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 Monday was 369 in Ghaziabad, 368 in Noida, 349 in Greater Noida, 353 in Faridabad and 306 in Gurgaon, according to CPCB's Sameer app.
On Sunday, it was 416 in Ghaziabad, 416 in Noida, 402 in Greater Noida, 366 in Faridabad and 288 in Gurgaon. 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.