The noxious smog resulting from raging farm fires and unfavourable weather pushed pollution in Delhi-NCR towards the "emergency" zone on Wednesday, prompting authorities to order closure of schools till November 15 -- a second time in two weeks.
With the Central Pollution Control Board fearing a similar situation will prevail over the next two days, Chief Minister Arvind Kejriwal said the odd-even road rationing scheme can be extended if needed.
The Environment Pollution (Prevention and Control) Authority (EPCA) also extended the restrictions on dirty-fuel based industries in Delhi-NCR, hot mix plants and stone crushers till the morning of November 15, as the MeT department said strong winds are expected from Friday, which will bring down the air pollution levels to the very poor category.
The schools in the national capital will be closed on Thursday and Friday, the Delhi government said.
On November 1, the Supreme Court-mandated panel EPCA declared a public health emergency as air pollution neared the emergency levels and the administration ordered closure of schools till November 5.
The city's overall air quality index read 456 at 4 pm, up from 425 at 4 pm on Tuesday.
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Rohini and Dwarka Sector-8 were the most-polluted areas with an AQI of 494, followed by Nehru Nagar (491) and Jahangirpuri (488).
Faridabad (448), Ghaziabad (481), Greater Noida (472), Gurgaon (445) and Noida (479) also choked on extremely polluted air.
In neighbouring Haryana, Hisar and Bhiwani (470) districts reported the worst air quality, followed by Jind (445), Fatehabad (430), Sirsa (415), Rohtak (412) and Panipat (408).
In Punjab, Amritsar's AQI was 362, followed by Bathinda (333), Patiala (285) and Jalandhar (276).
An AQI between 201 and 300 is considered 'poor', 301-400 'very poor' and 401-500 'severe'. An AQI above 500 falls in the 'severe plus' category.
The levels of PM 2.5 - tiny particulate matter less than 2.5 microns in diameter that can enter deep into the lungs and even the bloodstream - breached the emergency threshold of 300 micrograms per cubic metre in Delhi-NCR on Tuesday night and shot up to 354 micrograms per cubic metre, around six times the safe limit of 0-60, in the morning.
The levels of PM10 increased to 506 micrograms per cubic metre in the morning, more than five times the safe limit of 100 micrograms per cubic metre.
According to weather experts, a fall in the temperature and wind speed led to the accumulation of pollutants. The problems were compounded by a cloud cover that blocked sunlight.
Incidents of stubble burning in Haryana and Punjab have increased and northwesterly winds have been bringing more farm fire plume to the Delhi-NCR region, they said.
However, they said, the situation is likely to improve on Friday with an increase in wind speed due to a fresh western disturbance and a dip in farm fires.
A large number of children were exposed to the harmful spike in pollution as schools remained opened on Wednesday.
Pictures of schoolchildren with their faces covered with anti-pollution masks and handkerchiefs were shared widely on social media.
Scores of people also posted pictures of open burning of garbage and heaps of construction waste and dirt lying uncovered in several areas across the city.
As the air quality neared the emergency levels for the third time in less than a fortnight, Kejriwal said the road rationing scheme could be extended beyond November 15.
Reacting to it, Union Environment Minister Prakash Javadekar said, "We have seen that within 10 days of the implementation of the odd-even scheme, it (AQI) reached 600 as well as 200. Therefore, I do not want go into what connection it has with odd-even."