Delhi-NCR woke up to the pungent smell of smoke from firecrackers on a hazy Sunday morning as pollution levels in the region crossed the 'emergency' threshold.
The air quality had turned 'severe' on Saturday evening with stubble burning accounting for 32 per cent of Delhi's PM2.5 pollution, but firecracker emissions and calm winds made the situation even worse.
The levels of PM2.5 which is about three per cent the diameter of a human hair and can lead to premature deaths from heart and lung diseases were 396 microgram per cubic metre (g/m3) in Delhi-NCR at 6 am, above the emergency threshold of 300 g/m3.
The safe limit is 60 g/m3.
PM10 level stood at 543 g/m3 at 6 am, above the emergency threshold of 500 g/m3, according to Central Pollution Control Board (CPCB) data. PM10 levels below 100 g/m3 are considered safe in India.
According to the Graded Response Action Plan (GRAP), the air quality is considered in the 'severe plus' or 'emergency' category if PM2.5 and PM10 levels persist above 300 g/m3 and 500 g/m3 for more than 48 hours.
A large number of people burst crackers across the national capital and its suburbs on Saturday night, flouting the ban imposed by the National Green Tribunal.
Delhi Police arrested 10 people and seized 638 kg of firecrackers on Saturday.
The National Green Tribunal (NGT) had on Monday imposed a total ban on sale or use of all kinds of firecrackers in the National Capital Region (NCR) from November 9 midnight to November 30 midnight, saying 'celebration by crackers is for happiness and not to celebrate deaths and diseases'.
According to the Ministry of Earth Sciences' air quality monitor, SAFAR, the PM2.5 concentration in Delhi on Diwali could have been the 'lowest' in the last four years if there were no fireworks.
The city recorded an overall AQI of 414 at 4 pm on Saturday. It soared to 454 by 10 pm. On Sunday, it stood at 465 at 9 am.
The neighbouring cities of Faridabad (438), Ghaziabad (483), Greater Noida (439), Gurgaon (424) and Noida (466) also recorded their AQI in the severe category.
Delhi recorded a 24-hour average AQI of 337 on Diwali last year (October 27), and 368 and 400 in the next two days. Thereafter, pollution levels remained in the 'severe' category for three days on the trot.
In 2018, the 24-hour average AQI (281) on Diwali was recorded in the 'poor' category.
It deteriorated to 390 the next day and remained in the 'severe' category on three consecutive days thereafter.
In 2017, Delhi's 24-hour average AQI on Diwali (October 19) stood at 319.
It, however, slipped into the 'severe' zone the next day.
This time, the India Meteorological Department has said that a fresh western disturbance is likely to increase the wind speed and improve the air quality in Delhi-NCR post Diwali (Sunday and Monday).
Light rain is likely on Sunday under the influence of a western disturbance.
The air quality is likely to improve due to an expected increase in the wind speed, Kuldeep Srivastava, the head of the IMD's regional forecasting centre, said.
V K Soni, the head of the IMD's environment research centre, said high-velocity east-southeasterly winds (gusting up to 40 kilometre per hour) are expected to disperse the pollutants.
There will be a significant improvement in air quality by Monday, Soni said.
The Air Quality Early Warning System for Delhi also said the situation is likely to 'improve significantly' on Sunday.
'Under the influence of a Western Disturbance, isolated rainfall over plains of northwest India and adjoining central India is likely on Sunday.
'Generally cloudy sky, light rain, thundershowers accompanied with gusty winds (speed 30-40 kmph) is likely towards afternoon-evening on Sunday,' the central agency said.