The CPCB states that an AQI in the "poor" category may cause breathing discomfort.
The air quality deteriorated to reach "very poor" level in Ghaziabad and Greater Noida, while "poor" in Noida, Gurgaon and Faridabad, 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 319 in Ghaziabad, 331 in Greater Noida, 280 in Noida, 222 in Faridabad and 221 in Gurgaon, according to CPCB's Sameer app.
On Tuesday, it was 282 in Ghaziabad, 290 in Greater Noida, 243 in Noida, 196 in Faridabad and 184 in Gurgaon.
It was 243 in Ghaziabad, 256 in Greater Noida, 176 in Noida, 120 in Faridabad and 101 in Gurgaon.
On Sunday, it was 318 in Ghaziabad, 332 in Greater Noida, 322 in Noida, 303 in Faridabad and 239 in Gurgaon, according to the app.
The CPCB states that an AQI in the "poor" category may cause breathing discomfort to people, while "moderate" may cause breathing discomfort to the people with lungs, asthma and heart 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.
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