Delhi’s air quality was on the brink of the “severe” category again on Tuesday a day after it briefly improved to the “poor” range as winds continued to remain calm leading to a gradual deterioration in pollution. An Air Quality Index (AQI) of 394 (very poor) was recorded at 8am.  By 4 pm, it stood at 343 ( very poor) and 383  by 7 pm. The wind speed remained below 4 km per hour, which failed to disperse the pollutants. Predicted maximum mixing depth was traced to be 1650 m. The ventilation index lower than 6000 m2/s with average wind speed less than 10 kmph is unfavourable for dispersion of pollutants.

The 24-hour average AQI was 285 (poor) at 9am on Monday. By 4 pm, it deteriorated to 349 (very poor) and 377 by 7pm, and 391 by 10pm.An AQI of 318 (very poor) was recorded at 4pm on Sunday and 412 (severe) on Saturday. The last time Delhi’s AQI was below 300 was on October 29.

Seventeen out of 39 stations recorded “severe” AQI at 8am and the rest “very poor” on Tuesday. The highest AQI of 443 was recorded in Mundka, followed by 432 at East Delhi’s Anand Vihar and  432 at Rohini. According to IQ Air, PM2.5 concentration is currently 34.7 times the World Health Organization annual PM2.5 guideline value at 11.30 am. A thick layer of smog covered the National Capital as the Air Quality Index in several areas continues to remain in the ‘Very Poor’ category.

The Centre's Decision Support System (DSS) for Air Quality Management estimated that vehicular emissions contributed 22.004 per cent to Delhi's pollution on Tuesday.  Notably, there is a ban on entry of non essential trucks from other states to Delhi and around four lakh vehicles are off the road due to stage IV of the Graded Response Action Plan imposed in the Delhi-NCR. The contribution of the residential sector to air pollution is estimated 5. 393 percent, industries contributed 4.173  percent, construction 3.251 percent, energy sector 1. 564 percent, waste burning 1.651 percent, and road dust 1.686 percent.

According to DSS,  shallow fog reported at Safdarjung airport during early morning today. Safdarjung airport recorded lowest visibility 700 m at 0230 hours IST which improved thereafter becoming 800m at 0530 hours IST. Mainly clear sky condition with wind speed less than 10 kmph west direction prevailed over the region in the forenoon.

Meanwhile, the city's minimum temperature settled 0.6 notches above normal at 11.9 degrees Celsius, the India Meteorological Department said.