The central government's Air Quality Early Warning System for Delhi said slow winds and ventilation conditions are "extremely unfavourable" for dispersion of pollutants.
Delhi’s minimum temperature rose to 6.7 degrees Celsius, a notch above normal, on Friday due to partly cloudy weather, the India Meteorological Department (IMD) said.
However, “moderate” fog lowered visibility to 201 metres at Safdarjung and 300 metres at Palam in the morning, an IMD official said.
“Dense” fog is predicted in parts of the city on Saturday.
According to the IMD, “very dense” fog is when visibility is between 0 and 50 metres. In case of “dense” fog, visibility is between 51 and 200 metres, “moderate” 201 and 500 metres, and “shallow” 501 and 1,000 metres.
On Friday, the Safdarjung Observatory, which provides representative data for the city, recorded a minimum of 2 degrees Celsius, five notches below normal. It was 3.2 degrees Celsius on Wednesday.
Cold and dry northerly/northwesterly winds from the western Himalayas brought the minimum temperature down in Delhi on Thursday. The wind direction then changed to northeasterly. This, along with partly cloudy weather, resulted in an increase in the minimum temperature, Kuldeep Srivastava, the head of the IMD’s regional forecasting centre said.
On January 1, the city had recorded a minimum of 1.1 degrees Celsius, lowest for the month in 15 years.
The city’s air quality remained “severe” on Friday as well.
The air quality index had entered the “severe” zone on Thursday due to the prevailing “extremely unfavourable” conditions for dispersion of pollutants, government agencies said.
The city’s air quality index (AQI) was 460 at 10 am. The 24-hour average AQI was 429 on Thursday. It was 354 on Wednesday, 293 on Tuesday and 243 on Monday.
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”.
Srivastava said the wind speed has slowed down and the moisture in the air has made the pollutants heavier.
The central government’s Air Quality Early Warning System for Delhi said slow winds and ventilation conditions are “extremely unfavourable” for dispersion of pollutants.
This will lead to further deterioration in air quality, the agency said.