Dense fog reduced visibility to just 100 metres in parts of Delhi on Thursday, affecting traffic movement, the India Meteorological Department (IMD) said.
The minimum temperature at the Safdarjung Observatory, which provides representative data for the city, settled at 4.5 degrees Celsius.
“Dense fog in the Palam area reduced visibility to 100 metres between 5:30 am and 8 am. At Safdarjung, moderate fog lowered visibility to 201 metres,” Kuldeep Srivastava, the head of the IMD's regional forecasting centre said.
According to the weather department, “very dense” fog is when visibility is between 0 and 50 metres, 51 and 200 is “dense”, 201 and 500 “moderate”, and 501 and 1,000 “shallow”.
Cold wave conditions are predicted in parts of Delhi over the next two days. The mercury is expected to drop to three Celsius on Friday.
“Moderate to dense” fog is also expected during the period, the IMD said.
For the plains, the IMD declares a cold wave when the minimum temperature is 10 degrees Celsius or below and is 4.5 notches less than normal.
High humidity, low wind speed and lowering temperatures kept Delhi's air quality in the "severe" zone for the third day on the trot, according to weather department officials.
No major improvement is predicted till December 26, Srivastava said.
The city's air quality index (AQI) was 427 at 9 am. The 24-hour average AQI was 433 on Wednesday and 418 on Tuesday.
Air pollution in the neighbouring cities of Faridabad (450), Ghaziabad (442), Greater Noida (454) and Noida (448) also remained in the “severe” zone.
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".