Delhi's overall air quality is predicted to remain in the 'poor' to the lower end of 'very poor' category until the morning of October 24, according to the System of Air Quality and Weather Forecasting And Research (SAFAR).
Transport-level winds from Punjab, Haryana and Uttar Pradesh towards Delhi will pick up from October 24 and, in all likelihood, will bring significant stubble-related emissions to Delhi, SAFAR said.
The city's 24-hour average AQI was recorded in the 'poor' category at 265 on Saturday as residents flouted the ban on firecrackers in parts of the national capital ahead of Diwali, according to Central Pollution Control Board's (CPCB) data.
An AQI between zero 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.
"If stubble burning increases gradually, which is likely, its share in Delhi's PM2.5 (based on the average temporal variability of fire counts in the previous years) is likely to be 5 per cent on the October 23, 8 per cent on October 24 and 16 to 18 per cent on October 25," SAFAR's predictions said.
"Adverse weather conditions may bring firecracker-related pollution from surrounding regions of Delhi (outside NCT) and with 15 to 18 per cent stubble burning contribution, the AQI is predicted to touch the upper end of 'very poor' to lower end of 'severe' on October 25 (without emission from firecrackers in Delhi)," the predictions said.
SAFAR further predicted that in case there was emission from firecrackers, along with other factors, the AQI would worsen to 'severe' on Diwali (October 23) and might continue to remain the same for the next two days (October 24 and October 25).
"Air quality might improve slightly on October 26 evening onwards to the lower end of 'very poor' category as surface winds will pick up on October 26 and stubble transport level winds will slow down," the predictions said.
Predicting the air quality to deteriorate by the weekend, the Commission for Air Quality Management (CAQM) had on Wednesday directed authorities to enact Stage II of the Graded Response Action Plan (GRAP) -- a set of anti-air pollution measures followed in the national capital and its vicinity, according to the severity of the situation.
The Stage II plan includes banning the use of coal and firewood in hotels, restaurants and open eateries. The use of diesel generators, except for essential services, is also banned.
GRAP is classified under four stages, depending on the air quality in Delhi. Stage I is implemented in case of 'poor' air quality (AQI 201-300); Stage II for 'very poor' (AQI 301-400); Stage III for 'severe' (AQI 401-450) and Stage IV for 'severe plus' (AQI >450).
If the situation turns 'severe' (Stage III), authorities will have to enforce a ban on construction and demolition activities in NCR, except on essential projects (such as railways, metros, airports, ISBTs, national security/defence-related projects of national importance) and non-polluting activities such as plumbing, carpentry, interior decoration and electrical works.
Brick kilns, hot mix plants and stone crushers not operating on clean fuels and mining and associated activities in NCR will also be banned.
The state governments in Delhi-NCR may also impose restrictions on Bharat Stage (BS)-III petrol and BS-IV diesel light motor vehicles (four wheelers).
The measures in the 'severe plus' category or Stage IV include a ban on the entry of trucks into Delhi and on the plying of Delhi-registered diesel-run medium goods vehicles and heavy goods vehicles in the national capital, except those carrying essential commodities.
Four-wheeled diesel light motor vehicles, except BS-VI and those engaged in essential services, will also be banned in Delhi and bordering districts of NCR.
Stage IV will also trigger a ban on industries running on dirty fuels and construction and demolition activities in linear public projects such as highways, roads, flyovers, over bridges, power transmission and pipelines.