A layer of haze lingered over the national capital on Sunday as air quality in several parts of the city plunged to “very poor” category, days before strict measures to fight air pollution come into force under the Graded Response Action Plan (GRAP) .

The Air Quality Index (AQI) in Anand Vihar was 327; Wazirpur 323; Vivek Vihar 317; Mundka 309; Bawana 302; and in Jahangirpuri 300, according to Central Pollution Control Board data.

The overall AQI deteriorated further and touched the 268 mark, which falls in the poor category.

The air quality in neibhouring Ghaziabad (320) and Noida (310) in Uttar Pradesh and Haryana’s Alipur Khalsa (351) and Panipat (339) also turned “very poor” by 4.30 pm.

Faridabad, Greater Noida, Baghpat, Murthal recorded an AQI at 290, 233, 280, 259 and 245 respectively.

An AQI between 0 and 50 is considered ‘good’; 51 and 100 ‘satisfactory’; 101 and 200 ‘moderate’; 201 and 300 ‘poor’; 301 and 400 ‘very poor’; and 401 and 500 ‘severe’

Perturbed by the situation, Delhi Chief Minister Arvind Kejriwal tweeted, “All the gains achieved so far on pollution front will be nullified. Whereas, we need to do a lot in Delhi and we are trying, however, all governments and all agencies need to work to stop crop burning also (sic).”

On Saturday, he had said smoke from crop residue burning in neighbouring States was reaching Delhi and the air quality has started deteriorating.

“It has been widely reported that the smoke coming to Delhi is due to the burning of stubble in Karnal, Haryana,” he had said.

The Centre-run System of Air Quality and Weather Forecasting and Research said smoke from stubble burning will make up six per cent of Delhi’s pollution by October 15, when GRAP comes into force in the Delhi-NCR region.

Prepared by Central Pollution Control Board, GRAP lists various measures to be taken according to severity of pollution.

The 10-member task force on the GRAP had on Friday held a meeting on the stubble burning incidents reported from Punjab and Haryana, and its likely impact on Delhi-NCR’s air quality.

V K Soni, a senior scientist at the India Meteorological Department, who attended the meeting, said winds are calm due to monsoon withdrawal, leading to low dispersion of pollutants.

Also, wind direction has changed to west and north-west, he said.

Westerly and north-westerly winds bring dust from western regions and smoke caused by burning of crop residue in neighbouring Punjab and Haryana to Delhi-NCR.

Though Haryana has reported a slight decrease in the number of stubble burning incidents, Punjab has reported a massive increase of 45 per cent in such cases till October 11, according to data of pollution control boards of the two states.

Despite a ban on stubble burning in Punjab and Haryana, farmers continue to defy it amid a lack of financial incentives.

State governments are providing 50 to 80 per cent subsidy to farmers and cooperative societies to buy modern farm equipment for in-situ management of paddy straw and running a massive awareness campaign against stubble burning.

Starting October 15, stricter measures to fight air pollution will come into force in Delhi and its neighbourhood as part of GRAP, which was first implemented in Delhi-NCR in 2017.

These measures include increasing bus and metro services, hiking parking fees and stopping use of diesel generator sets when the air quality turns poor.

When the situation turns “severe”, GRAP recommends closure of brick kilns, stone crushers and hot mix plants, sprinkling of water, frequent mechanised cleaning of roads and maximising power generation from natural gas.

The measures to be followed in the “emergency” situation include stopping entry of trucks into Delhi, ban on construction activities and introduction of the odd-even car rationing scheme.