The air quality was recorded "severe" in Ghaziabad and Greater Noida, while it remained "very poor" across Noida, Faridabad and Gurgaon, according to a government agency data on Wednesday. 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 Wednesday was 421 in Ghaziabad, 406 in Greater Noida, 394 in Noida, 326 in Faridabad and 324 in Gurgaon, according to CPCB's Sameer app. On Tuesday, it was 424 in Ghaziabad, 388 in Greater Noida, 387 in Noida, 335 in Faridabad and 311 in Gurgaon.
The CPCB states that an AQI in the "very poor" category may cause respiratory illness on prolonged exposure, while "severe" affects even healthy people and seriously impacts those with existing diseases. 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.