Delhi's air quality was recorded in the "poor" category on Monday and is expected to deteriorate slightly over the next three days, according to the authorities.
As per the Central Pollution Control Board (CPCB) data, the overall air quality index (AQI) in the city was 267, which falls in the "poor" category.
An AQI between 100 and 200 comes under "moderate" category, 201 and 300 is considered "poor", 301 and 400 "very poor", while that between 401 and 500 is "severe".
In the National Capital Region, Ghaziabad, Noida and Greater Noida also recorded "poor" air quality, it said.
The overall PM2.5 level -- fine particulate matters in the air with a diameter of less than 2.5 micrometers -- in Delhi was 123, while the PM10 level was 206, it said.
The centre-run System of Air Quality and Weather Forecasting (SAFAR) said current air quality of Delhi is in ''poor'' category.
"The moderate wind speed is preventing it to cross to next level (very poor). Cold wave conditions and moderate fog is likely to prevail for next two days. Hence, air quality is predicted to deteriorate slightly but will fluctuate between very poor to poor for next three days," SAFAR said.