After a week of clear weather, the capital woke up to dense fog Wednesday morning. Officials at the MeT department have forecast dense fog on Thursday as well, but said the occurrence does not indicate a start to seasonal fog. Due to the fog, 15 flights were diverted at IGI Airport, 47 delayed and one cancelled.
Pollution levels in the city also spiked after wind speed dropped and moisture increased. “The fog spell is likely to last one to two days for three hours in the morning. The fog is not expected to stay as night-time temperature, which is a crucial factor in the formation of fog, is starting to rise. Fog formation is aided by a dip in temperature — which is a prime parameter that supports the formation of dense fog night after night. This is usually observed between December and February,” said a Met department official.
According to officials, the primary reason behind the formation of fog was a sudden increase in humidity across the city. The layer of dense fog over the Indo-Gangetic Plain, which was developing since Monday, expanded and covered the capital.
The drop in wind speed, increased humidity and dip in temperature also contributed to the increase in pollution levels in the city. While the Central Pollution Control Board put Delhi’s air in the “severe” category, with a reading of 419 on the air quality index, SAFAR’s monitoring system said Delhi’s air was “very poor”.
The 24-hour-average of particulate matter 2.5 and 10 was 182 and 343 micrograms per cubic metre respectively. The safe limits are 60 and 100.
Air quality in the capital improved last week from “very poor” to “moderate” and “poor” at most stations, primarily because of strong winds and relatively high temperature.
“In the absence of any stringent emission control measure, air quality becomes totally dependent on meteorological factors such as temperature and wind speed. In adverse conditions, pollutants do not disperse and the air quality dips,” said TERI fellow Sumit Sharma.