The rapid fall in air quality and visibility began last evening itself as moisture combined with pollutants shrouded the city in a thick cover of haze.
By 10 am today, the Central Pollution Control Board (CPCB) recorded 'severe' air quality, meaning the intensity of pollution was extreme.
In light of the sudden dip, measures under the Graded Response Action Plan (GRAP) such as a four times hike in parking fees may be rolled out by the Supreme Court-mandated Environment Pollution Prevention and Control Authority.
If the situation deteriorates further and persists for at least 48 hours, the task force under the GRAP will mull shutting schools and enforcing the odd-even car rationing scheme.
The last time air had turned 'severe' was on October 20, a day after Diwali festivities, when firecrackers were set off.
Since then, the pollution monitors have been recording 'very poor' air quality, which is comparatively better than 'severe' but still alarming according to global standards.
The CPCB has said high moisture level in the air has trapped emission from local sources and hanging low over the city in the absence of wind.
According to private weather forecasting agency Skymet, wind from neighbouring Punjab and Haryana, where paddy stubble burning is in full swing, has started entering the city during the afternoon hours.
The CPCB also recorded 'severe' air quality in the neighbouring Noida and Ghaziabad.
The real-time pollution monitors displayed alarmingly high concentration of PM2.5 and PM10, which are ultrafine particulates having the ability to enter the respiratory system and subsequently the bloodstream of humans and animals, causing harm.