Delhi woke up to hazy skies with pollution levels in the red or "severe" category for the sixth consecutive day today. The national capital's pollution level has risen to 487 points, with a blanket of smog hanging over the city.
The last time this happened was in 2017, when Delhi's air quality was highly toxic for a week from November 7 to 13.
The reasons for that long episode included a dust storm that swept Saudi Arabia, Iraq and Kuwait before making its way to Delhi.
This time, even without any adverse weather phenomenon or contribution from other sources, the pollution level has been in "severe" category since November 5.
Among the factors that could have added to falling air quality is crop stubble burning, which continues in Punjab and Haryana.
Also, stagnant air doesn't allow pollutants to be swept away from the city. There is also secondary aerosol formation, which happens when there is a lot of moisture in the air, thus the capacity to hold on to pollutants increases significantly over a longer period of time.
All these combined have led to Delhi's air being choked with no respite in sight.
This is for the first time that air quality in Delhi is bad for a long stretch without any contributing factor from firecrackers bursting or a weather phenomenon.