Visibility improves as Delhi witnesses moderate fog; air quality deteriorates

The 24-hour average air quality index (AQI) was very poor at 382 at 4pm on Friday, and it further worsened to 399 at 9am on Saturday

New Delhi: Moderate fog was witnessed in parts of Delhi on Saturday morning, with the lowest visibility recorded at 200 metres at Safdarjung, the capital’s main weather station, according to the Indian Meteorological Department (IMD).

(Representative Photo)

Visibility at Palam remained above 500 metres having a lesser impact on flight operations as compared to previous days.

The IMD classifies fog as ‘shallow’ when visibility is between 500 and 1000 metres, ‘moderate’ between 200 and 500 metres, ‘dense’ between 50 and 200 metres and ‘very dense’ when it is lower than 50 metres.

The capital’s air quality meanwhile deteriorated to the upper end of the ‘very poor’ category and is likely to touch ‘severe’ later in the day. The 24-hour average air quality index (AQI) was very poor at 382 at 4pm on Friday, and it further worsened to 399 at 9am on Saturday. An AQI over 400 is classified as ‘severe’.

The Indira Gandhi International Airport (IGIA) reported no flight cancellations or diversions on Saturday, but around 10 flights were delayed in the early hours. Northern Railway meanwhile said at least 30 trains to and from Delhi were running at a delay of more than one hour.

The IMD had forecast chances of moderate to dense fog across the capital for Saturday, with a yellow alert in place for similar weather for Sunday as well. Upper-level fog on Friday also meant Delhi’s maximum temperature dipped below 20 degrees Celsius for the first time this season.

Delhi’s maximum was recorded at 19.8 degrees Celsius, a degree below normal for this time of the year. The previous lowest maximum so far this season had been 21.4 degrees Celsius, which was recorded a day earlier. The IMD says Delhi’s maximum is likely to hover around 18-19 degrees Celsius today and tomorrow, with isolated parts even recording ‘cold day’ conditions.

The IMD classifies a ‘cold day’ when the maximum temperature is 4.5 degrees Celsius or more below normal with the minimum also being below 10 degrees Celsius. While the maximum criteria were met at some stations, the minimum was not. The minimum temperature at Safdarjung was recorded at 10.7 degrees Celsius on Friday – four degrees above normal. It was as high as 13.7 degrees Celsius at Pitampura. This rose even further on Saturday morning, with Safdarjung recording a minimum temperature of 11.8 degrees Celsius.

“With such a layer of fog persisting over a city, night-time temperature rises, as heat gets trapped within the atmosphere. The same layer of fog, both at the surface level and in the upper level of the atmosphere, makes days cold, as sunlight does not penetrate through, narrowing the gap between maximum and minimum,” senior scientist Kuldeep Srivastava explained, stating cold is felt more tangibly in such a scenario.