Delhi's air quality plummeted to the "severe plus" category on Friday morning, a stage at which all emergency measures, including a ban on polluting trucks, commercial four-wheelers, and all types of construction, are mandated to be initiated and enforced in the National Capital Region.

These measures constitute the final stage of the Centre's air pollution control plan and should ideally be activated at least three days prior to the Air Quality Index (AQI) surpassing the 450 mark in the capital, as outlined in a policy document prepared by the Commission for Air Quality Management (CAQM).

The CAQM, a statutory body responsible for formulating strategies to combat pollution in the region, ordered a ban on non-essential construction work and specific categories of polluting vehicles on November 2.

However, it has not yet called upon Delhi and NCR states to implement all emergency measures, which also include work-from-home directives for government and private offices.

Under the final stage (Stage IV) of the Graded Response Action Plan, only CNG, electric, and BS VI-compliant vehicles from other states are allowed to enter Delhi, with exemptions granted to those involved in essential services.

All medium and heavy goods vehicles not engaged in essential services are also required to be banned in the capital.

The city's AQI skyrocketed from 351 at 10 am on November 2 to 471 at 9 am on Friday, reflecting a sudden increase in pollution levels due to highly unfavourable meteorological conditions and a sharp spike in stubble burning incidents in neighbouring states.

Delhi's 24-hour average AQI, recorded at 4 pm each day, was 392 on Thursday, 364 on Wednesday, 359 on Tuesday, 347 on Monday, 325 on Sunday, 304 on Saturday, and 261 on Friday.

These numbers indicate a gradual deterioration in Delhi's air quality over the past few days, culminating in a descent into the severe category on November 2.

The air crisis is not confined to Delhi alone; several cities in neighbouring Haryana, Rajasthan, and Uttar Pradesh have also reported hazardous air quality.

These cities include Hanumangarh (401), Bhiwadi (379), and Sri Ganganagar (390) in Rajasthan; Hisar (454), Fatehabad (410), Jind (456), Rohtak (427), Ballabgarh (390), Bahadurgarh (377), Sonepat (458), Kurukshetra (333), Karnal (345), Kaithal (369), Bhiwani (365), Faridabad (448), and Gurugram (366) in Haryana; and Ghaziabad (414), Baghpat (425), Meerut (375), Noida (436), and Greater Noida (478) in Uttar Pradesh.

As a dense and pungent haze lingers over Delhi-NCR for the fourth consecutive day on Friday, the concentration of PM2.5, fine particulate matter capable of penetrating deep into the respiratory system and triggering health problems, exceeded the safe limit of 60 micrograms per cubic metre by seven to eight times at multiple locations throughout the region.

Invoking Stage III of the pollution control plan, the CAQM on Thursday ordered an immediate ban on non-essential construction work, stone crushing and mining in the region.

Restrictions have also been imposed on the plying of BS III petrol and BS IV diesel four-wheelers in Delhi, Gurugram, Faridabad, Ghaziabad and Gautam Budh Nagar.

GRAP categorises actions into four stages: Stage I - 'poor' (AQI 201-300); Stage II - 'very poor' (AQI 301-400); Stage III - 'severe' (AQI 401-450); and Stage IV - 'severe plus' (AQI above 450).

The Delhi government has also announced the closure of all primary schools for two days in an effort to safeguard young children from health-threatening pollution.

Delhi Environment Minister Gopal Rai has called an emergency meeting on Friday to review the situation.

The CAQM has said the pollution levels are only "expected to increase further" owing to highly unfavourable meteorological and climatic conditions.

"We expect the unfavourable weather conditions – low wind speed, non-conducive wind direction and lack of rain – to persist for another two to three days, allowing for further accumulation of pollutants," a scientist at the India Meteorological Department (IMD) said.

The IMD reported visibility levels of only 500 metres at the Safdarjung Observatory and the Palam Observatory around 10 am.

Health professionals have expressed concerns that air pollution is increasing asthma and lung problems in children and the elderly.

"We are recording a surge in the number of irritative bronchitis infections. It is recommended that people suffering from respiratory issues such as chronic bronchitis and asthma take their medicines regularly and do not go out in the open unless absolutely necessary," said Jugal Kishore, the head of the medicine department at Safdarjung Hospital.

Considering the spike in indoor pollution in Delhi, he advised people to use air purifiers in their homes.

Unfavourable meteorological conditions, combined with emissions from firecrackers, paddy straw burning, and local pollution sources, contribute to hazardous air quality levels in Delhi-NCR during winter.

According to an analysis conducted by the Delhi Pollution Control Committee (DPCC), the capital experienced peak pollution from November 1 to November 15 when the number of stubble-burning incidents in Punjab and Haryana increased.

Air pollution in India resulted in 1.67 million deaths in 2019 -- the largest pollution-related death toll in any country in the world -- and accounted for USD 36.8 billion in economic losses, according to a new study by researchers from the Global Observatory on Pollution and Health at Boston College, the Indian Council of Medical Research, and the Public Health Foundation of India.

One of the major reasons behind the accumulation of pollutants in recent days is the lack of rainfall during this post-monsoon season so far.

In contrast to October 2022 (129 mm) and October 2021 (123 mm), Delhi experienced only one rainy day (5.4 mm of precipitation) in October 2023. There has been no rain in November so far.

According to a numerical model-based system developed by the Indian Institute of Tropical Meteorology in Pune, smoke from stubble burning accounted for 25 per cent of the PM2.5 pollution in Delhi on Thursday, and this figure may rise to 35 per cent on Friday.

The CAQM recently reported that the number of stubble-burning incidents in Punjab and Haryana between September 15 and October 29 reduced by around 56 per cent and 40 per cent, respectively, compared to the corresponding period last year.

However, the agrarian states have seen a significant jump in farm fires over the last few days -- 1,852 on October 30; 2,901 on October 31 and 2,386 on November 1.

An official from the Delhi-based Indian Agricultural Research Institute said Punjab and Haryana experienced an increase in paddy production this year due to the lack of cloud cover, resulting in an abundance of paddy straw.

The Punjab government aims to reduce farm fires by 50 per cent in this winter season and eliminate stubble burning in six districts.

According to Punjab's action plan to curb paddy straw burning, about 31 lakh hectares of land in the state are under paddy cultivation and expected to generate around 16 million tonnes of paddy straw (non-basmati).

Haryana estimates that about 14.82 lakh hectares of land in the state are under paddy cultivation and expected to generate over 7.3 million tonnes of paddy straw (non-basmati). The state is making efforts to nearly eliminate farm fires this year.

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