The air quality remained "moderate" to "poor" on Tuesday in Faridabad, Gurgaon, Gautam Buddh Nagar and Ghaziabad in the National Capital Region, according to a government agency.
There was concentration of PM 2.5 and PM 10 pollutants in the air of the four immediate 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 Faridabad, the AQI was recorded at 262 at the station in Sector 11 followed by 244 at Sector 30, 217 at New Industrial Town and 199 at Sector 16A, according to the CPCB data at 7 pm.
In Gurgaon, an AQI of 246 was recorded at the station in Sector 151 followed by 234 at Vikas Sadan, 169 at NISE Gwal Pahari and 131 at the Teri Gram, it showed.
In Gautam Buddh Nagar's Noida, the AQI of 235 was measured at Sector 1, 229 at Sector 62 and 195 at Sector 116, while the station at Sector 125 showed "insufficient" data for the last 24 hours.
In Greater Noida, an AQI of 239 was recorded in Knowledge Park V while it was 187 in Knowledge Park III, according to the CPCB figures.
Adjoining district Ghaziabad's Loni had an AQI of 267 at 7 pm followed by 209 at Indirapuram and 202 at Sanjay Nagar while no official data was available for Vasundhara, it showed.
The worsening of the air quality comes 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.