"Cold day" conditions gripped Delhi on Friday with its maximum temperature dipping to 15.4 degrees Celsius, five notches below normal, according to the India Meteorological Department (IMD). The minimum temperature settled at 6 degrees Celsius, a notch below the average temperature, the weather office said.
At Narela and Jafarpur, the maximum temperature dipped to 11 degrees Celsius and 12.1 degrees Celsius, nine and eight notches below normal, respectively. Similar conditions are predicted on Saturday too.
According to the IMD, a "cold day" is when the minimum temperature is less than 10 degrees Celsius and the maximum is at least 4.5 degrees Celsius below normal. In the morning, a thick blanket of fog shrouded the capital, lowering visibility to 50 metres at Safdarjung and Palam and affecting traffic movement.
When visibility due to fog is reduced to the range of 0 to 50 metres, it is categorised as "very dense" fog. In the case of "dense" fog, visibility is between 51 and 200 metres, "moderate" is 201 and 500 metres, and "shallow" is 501 and 1,000 metres. Dense to moderate fog is predicted in Delhi for the next four days, the IMD said.
The capital's air quality deteriorated further due to high humidity and the 24-hour air quality index (AQI) read 348 at 4 pm, as against 321 at the same time on Thursday. High moisture content in the air makes pollutants heavier, making dispersion difficult.
An AQI between zero and 50 is considered 'good', 51 and 100 'satisfactory', 101 and 200 'moderate', 201 and 300 'poor', 301 and 400 'very poor', and 401 and 500 'severe'.