Early morning fog, AQI dips

Delhi witnessed light fog on Wednesday morning, with visibility falling to as low as 350 metres in parts of the city. The fog resulted in the Capital’s AQI dropping to a reading 144 (moderate).

Delhi residents woke up to their first foggy morning of the season on Wednesday – a relatively rare phenomenon so early in the year – as visibility dropped nearly throughout the city following four days of near-consistent rainfall.

Kartavya Path shrouded in fog on Wednesday morning. (PTI)

Visibility in many parts of the city fell to around 300 metres in the early hours of the day as the hanging moisture in the air, coupled with low wind speeds and rising pollution levels aided fog formation – conditions that are likely to prevail over the next few days, India Meteorological Department (IMD) officials said.

Pollution levels, which were low for the past few days thanks to the rain, have also started climbing and are only expected to worsen in coming days, officials warned.

“This is the season’s first fog spell and it is generally rare to see it in the first half of October. Over the last three decades, we have only seen fog this early two or three times,” said RK Jenamani, SCIENTIST?/SENIOR SCIENTIST?, stating while visibility at Palam was between 300m and 350m, it was around 600m at Safdarjung.

“With adequate moisture in the air and dry northwesterly winds yet to start blowing towards Delhi-NCR, similar fog may be seen on Thursday and Friday too. However, the duration of the fog is only likely to be for a short period, dissipating as soon as the sun comes out,” he said.

The IMD classifies fog as ‘shallow’ when visibility is between 500m and 1,000m, as ‘moderate’ when it is between 200m and 500m, and as ‘dense’ when it is 200m or lower.

Delhi’s overall air quality index (AQI) reading at 4pm on Wednesday stood at 143, falling in the moderate category. This number was 66 (in the ‘satisfactory’ range) on Tuesday, according to data compiled by the Central Pollution Control Board.

With wind speeds expected to remain low and chances of fog occurring over the next two days as well, official forecasts show that Delhi’s AQI may drop to ‘poor’ by Friday.

“The overall air quality over Delhi is likely to remain in the ‘moderate’ category on Wednesday and Thursday. It is then likely to deteriorate and will be between ‘moderate’ to ‘poor’ category on Friday. On Saturday, it is likely to be in the ‘poor’ category,” said the forecast issued by the Early Warning System (EWS) for Delhi, which is used by the Commission for Air Quality Management (CAQM) to take pre-emptive action.

In terms of temperature, Delhi’s maximum and minimum continued to remain below normal. While the maximum was recorded at 30.3 degrees Celsius, three notches below normal, the minimum was 20.2°C, a degree below normal. Forecast for Thursday shows the maximum is likely to rise to around 32°C, but the minimum may drop further to 19°C. There are chances of fog in the early hours as well.

Last year, Delhi saw fog only towards the end of December, with October and November having relatively better visibility in the morning hours. In fact, in December, Delhi only saw a total of 90 fog hours, well below the average of 278 fog hours Delhi had been recording in the decade prior to 2021.