CPCB's air quality index (AQI) jumped from 229 to 368, with PM2.5 peaking above 400 micrograms per cubic metre—about six times the 24-hour standard—at many places like Anand Vihar, RK Puram and Punjabi Bagh. The wind speed was mostly below 1 metre per second.

Strong wind and high temperature that led to good air quality over NCR in the past fortnight are changing, said RavinderVishan, the scientist in charge of the regional meteorological centre. "Wind is likely to be easterly, north-easterly from November 30 to December 3. This will increase moisture in the air and reduce visibility over the Gangetic plains.The dispersion of aerosols will also reduce, leading to shallow-to-moderate fog at many places over UP and isolated dense fog over next three-four days."

Scientists at various monitoring agencies have indicated that pollution levels can once again be severe like the smog episode on November 5 and 6.