The air quality slipped to the "severe" category in Ghaziabad, while it remained "very poor" in Gurgaon, Faridabad and Gautam Buddh Nagar in the National Capital Region on Saturday, according to a government agency.
Concentration of major air pollutants PM2.5 and PM10 during the morning hours largely remained in the "severe" category in the four neighbouring districts 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'.
In Ghaziabad, an AQI of 412 was recorded at Loni station, followed by 363 at Vasundhara, 360 at Sanjay Nagar, 358 at Indirapuram, according to the CPCB data at 8 pm.
In Gautam Buddh Nagar's Noida, the AQI was 360 at Sector 62, 356 at Sector 1 and 315 at Sector 116.
The station at Sector 125 showed "insufficient" data for the last 24 hours.
In Greater Noida, an AQI of 391 was recorded at Knowledge Park V and 342 at Knowledge Park III, according to the CPCB figures.
In Gurgaon, an AQI of 379 was recorded at the station in Sector 51 followed by 342 at Teri Gram, 329 at Vikas Sadan and 266 at NISE Gwal Pahari, the CPCB data showed.
In Faridabad, the AQI was recorded 380 at New Industrial Town at 8 pm followed by 368 at Sector 11, 364 at Sector 30 and 324 at Sector 16A.
The concentration of PM2.5 and PM10 in Gurgaon, Faridabad, Gautam Buddh Nagar and Ghaziabad around 10 am was near or upwards of 400, in the "severe" category, according to the CPCB data.
Prolonged exposure to "very poor" air quality can lead to respiratory illnesses. "Severe" air quality also affects healthy people and seriously impacts those with existing ailments.
The air quality has been worsening even as the Graded Response Action Plan (GRAP) has been implemented in the Delhi-National Capital Region (NCR) from October 15 to check air pollution, which spikes around this time of the year.