The day-long average of PM 2.5 and PM 10, which are ultrafine particulates, were 178 and 94 micrograms per cubic metre (ug/m3), while the air quality index of the Central Pollution Control Board (CPCB) was poor.

An official of the CPCB attributed the rise in pollution levels to ground-level activities such as burning of paddy stubble in neighbouring Punjab and Haryana and meteorological conditions including a cyclonic circulation and a fall in wind speed that traps pollutants.

Winter is a critical time in Delhi as meteorological conditions trap air pollutants near the earth's surface.

The volume of pollutants also rises alarmingly due to the burning of paddy stubble in Haryana and Punjab and bursting of firecrackers during the festive season.

Last year, the air quality of Delhi had plunged and a dense blanket of smog had kept the city shrouded for over a week in November, soon after the Diwali festivities, prompting the authorities to announce closure of schools among other emergency measures.