Air quality plunges to 'severe' level in Noida, Ghaziabad, Faridabad

The average air quality plunged to "severe" level in Ghaziabad, Noida, Greater Noida and Faridabad, while it was "very poor" in Gurgaon, according to a 24-hour data issued by a government agency on Tuesday.

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 Tuesday was 458 in Ghaziabad, 450 in Greater Noida, 437 in Noida, 407 in Faridabad and 377 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 "severe" affects even healthy people and seriously impacts those with existing diseases.

The average AQI on Monday was 391 in Ghaziabad, 366 in Greater Noida, 363 in Noida, 289 in Faridabad and 271 in Gurgaon, while on Sunday it was 346 in both Ghaziabad and Greater Noida, 333 in Noida, 294 in Faridabad and 262 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.