These conditions can be attributed to the reversal of the wind direction. Dry and cold winds from the Northwest have been replaced by moist and relatively warm winds from the Southeast. The wind speed also remained light and humidity levels in the city increased.
The combination of light winds, high humidity levels and cold temperatures have resulted in foggy conditions over Delhi-NCR. The pollutants from industries, vehicles and dust particles from construction sites usually get mixed with fog resulting in the formation of smog.
Now, the winds will continue to blow from the southeast and speed will also be negligible. Thus, pollution will continue to affect the residents of Delhi-NCR for another 24 hours. A significant increase in the pollution levels will force Delhiites to breathe polluted air.
By December 24, as the Western Disturbance will move away, the usual pattern of dry and cold winds will resume. The wind speed will also increase. After that, dry weather conditions with strong winds will carry away the smog-forming pollutants.
Image credit: apwa.co.in