Authorities in the city scrambled to tackle the "emergency" situation as hospitals recorded a surge in the number of patients complaining of respiratory problems, reminiscent of the '1952 Great Smog of London'.
The smog, which triggered near zero visibility at many places and pile-ups on highways, is a mixture of carbon monoxide, particulate matter such as PM2.5, PM10, ground level ozone and oxides of nitrogen and sulphur dioxide, the Delhi government said in a health advsiory.
The metro and Delhi Transport Corporation announced decisions to augment services by pressing more trains and buses into service, in a bid to reduce dependence on private vehicles.
On Twitter, Chief Minister Arvind Kejriwal said it was "an emergency" and that his office was "continuously trying" to fix a meeting with his counterparts in Punjab and Haryna on stubble burning, a process that leads to air pollution in Delhi.
More From This Section
However, the Supreme Court-empowered Environment Pollution (Prevention and Control) Authority's member Sunita Narain cautioned against putting too much hope in temporary solutions such as closure of schools.
In its health advisory, the government said people should stay indoors as much as possible as the "smog is poisonous" and may create many health hazards like asthma attacks and other breathing complications.
The day-long average air quality index of the Central Pollution Control Board (CPCB) had a score of 478 on a scale of 500, indicating 'severe' levels of pollution, while many individual stations recorded AQI as high as 487.
If the score touches 500 and persists there for at least 48 hours, measures like odd-even and a ban on construction and demolition activities will come into force across the Delhi- NCR under the Graded Response Action Plan (GRAP).
"We will enforce odd-even in Delhi if air quality turns severe plus. I have also directed DTC to procure 500 buses on short-term basis to augment public transport till March. Metro has also been asked to hire around 300 buses for 15-20 days if odd-even is implemented," Gahlot said, adding that two- wheelers will be exempted from the scheme as and when it is rolled out.
But confusion prevailed over the measures already announced by the EPCA.
The civic bodies are also yet to announce any hike in parking fees.
"Cities and administrations need to implement solutions and take bold decisions to reduce emissions. The range of actions recommended and directed by the EPCA is targeted at doing just that, and it is now up to the political leadership of Delhi and NCR to take their implementation forward," Narain, who is also the chief of the Centre For Science and Environment (CSE), said.
It was the Environment Ministry which, in January, had empowered the EPCA through a gazette notification to enforce the GRAP to combat air pollution in the Delhi-NCR region.
Meanwhile, in incidents of pile-ups at multiple locations on the busy Yamuna Expressway over 20 vehicles collided and around 22 people suffered minor injuries during the morning hours when visibility was a measly 10 metres.
According to the forecast of the Union Ministry of Earth Sciences' System of Air Quality and Weather Forecasting And Research (SAFAR), the 24-hour-average concentrations of PM2.5 and PM10 will be around 420 and 678 micrograms per cubic metre.
The secretary of the Ministry of Earth Sciences, Madhavan Rajeevan, said the smog in Delhi is not localised, but spread across the entire region. He said the conditions would persist for another two-three days.
The SAFAR suggested that the "sudden" intrusion of pollutant-laden smoke from neighbouring Punjab and Haryana from the night of November 6 led to the spike as the high quantity of moisture in the city's air trapped the particulates.
"There is absolutely no wind movement. Moreover, temperature is also not coming down substantially which could have resulted in the conversion of the fog into water and subsequent dispersion of the suspended particulates," CPCB scientist Dipankar Saha explained.
Residents of the city complained of heavy breathing and watery eyes as the smog did not even spare living rooms or underground metro stations.
In London smog of 1952 about 4,000 people had died prematurely when average PM levels were about 500 microgramme per cubic metre along with high SO2 levels.
Yesterday, with a score of 448 in a scale of 500, the air quality index was at the year's worst.
The Indian Medical Association had declared a "public health emergency" and appealed to the government to stop outdoor sports and other such activities in schools to protect the health of children.