Due to the influence of La Nina, cold winter is expected in North India this year. There is also a possibility of cold wave in many districts of Rajasthan and Uttar Pradesh including Punjab, Haryana, Delhi. After the withdrawal of monsoon, when winter starts increasing in North India and the direction of the winds also becomes north-westerly, then air pollution also starts increasing. The most important reason for increasing air pollution can be linked to the process of stubble burning in western Uttar Pradesh, Haryana, Punjab and central Pakistan associated with light winds and formation of fog and mist.
When the temperature starts decreasing in North India, at that time mist, haze and fog starts forming in the morning hours. Cold air becomes heavier and stays near the ground. Fog and mist mixed with dust and smoke particles become smog. If the wind speed is very low, the layer of smog remains near the surface of the earth. Due to the low speed of winds, this air pollution is not able to move over a large area and due to the addition of new dust and smoke in it, it takes a very dangerous form.
Two weather parameters are very important to get relief from air pollution. The first of these is moderate to heavy rain. If there is heavy rain in North India, then the dust and smoke particles along with other pollutants get washed away and the atmosphere starts getting clean. Another important factor is the continuous movement of strong winds from the same direction.
In the winter season, when winds usually blow from north-west direction, these strong winds spread the air pollution far and wide, which gives a lot of relief. At present, air pollution is at its peak in many cities of North India including Delhi. Today, from the afternoon of November 6, strong winds are expected from the northwest direction, due to which there can be considerable relief from air pollution.
A cold winter does not always lead to more air pollution. Because due to the arrival of western disturbance in between, it rains in North India which reduces pollution. After the passage of the Western Disturbance, strong winds blow, which gives relief in pollution.