As pollution increases, it means that there are more suspended particles in the atmosphere which can serve as condensation nuclei on which water vapour can condense resulting in fog. If it is coupled with stagnant air & temperature inversion, conditions become very favourable for fog formation. A synoptic pattern like this is quite common during this time of year in northern India due to the combination of air pollution and a ridge of high pressure sitting across the country leading to air stagnation. As the Westerly jet stream continues to shift farther to the south as the winter progresses, Western Disturbances will help to eventually clear out the air by causing precipitation.
In last few days, pollution has combined with air stagnation across northern India and Pakistan to lead to extremely poor air quality during the past week. Without a significant change in the overall weather pattern, poor air quality and low visibility will last 48-72 hours.
Visibility from Islamabad, Pakistan to New Delhi and Varanasi, India has been reduced to few hundred meters & nil visibility at some places, frequently during the past several days due to the pollution and fog. Visibility at Palam Airport has dropped to zero on several occasions over the weekend. Due to the poor visibility, dense fog warnings have been extended, to now cover Bihar, West and East Madhya Pradesh regions.
Smog is so prevalent it had also been keeping daytime temperatures cooler than normal across this region. On Sunday maximum was 15°C at Delhi while minimum on Sunday was 6.4°C & on Monday morning the minimum fell further to 4.2°C. Cold day conditions are persisting over Central Pakistan & Northern India for past three days. In Central Pakistan places like Lahore, Jhelum, Dera Ismail Khan, Faisalabad etc. are observing diurnal range of 4-6°C. By Tuesday, a trough in Westerlies will move across northern India & could bring enough mixing to the atmosphere to help clear the air somewhat, but poor air quality will likely still be a problem into the middle of the week. By 25-26 December, a more significant system will cause the wind to change back to Northwesterlies across the region which will enhance the chances of more widespread clearing.
In such situations with poor air quality such as this, outdoor time should be limited,specially late night & early mornings, as pollution levels go up in night due to low temperatures.
