‘Dense fog’ blankets Delhi; visibility dips to zero at Palam

A dense fog blanketed Delhi for the first time this season on Wednesday, reducing visibility to zero at the Delhi airport as calm winds stalled the dispersion of pollutants, worsening air quality to the higher end of the “very poor” category. The average Air Quality Index (AQI) was 361 (“very poor”) at 8 a.m., up from 334 on Tuesday afternoon. Of Delhi’s 36 monitoring stations, only Ayanagar recorded a severe AQI of 417 at 8 a.m., while Lodhi Road (268) and Aurobindo Marg (275) logged “poor” air quality. This marked the 15th consecutive day of “very poor” air quality in the city.

According to the Central Pollution Control Board (CPCB), AQI ranges from 0-50 as “good,” 51-100 as “satisfactory,” 101-200 as “moderate,” 201-300 as “poor,” 301-400 as “very poor,” and above 400 as “severe.”

The India Meteorological Department (IMD) reported that visibility at the Delhi airport (Palam) was 100 meters at 6 a.m. before dropping to zero by 8:30 a.m. This first dense fog of the season in Delhi was mirrored across northwest India, with zero visibility at Amritsar and Hindon airports, 150 meters at Deoghar, and about 200 meters at Chandigarh and Gorakhpur. IMD classifies visibility between 500-1,000 meters as “shallow,” 200-500 meters as “moderate,” and 50-200 meters as “dense”; visibility under 50 meters is considered “very dense” fog. The lowest visibility previously recorded in Delhi this season was 700 meters at Safdarjung.

The IMD clarified that the phenomenon observed over the past two weeks was fog, not smog, and noted that fog is identified when relative humidity is above 75%, while smog combines high humidity with visibility under 1,000 meters.

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