Stubble burning is predicted to emerge as the highest contributor to Delhi's PM2.5 concentration, with air quality likely to deteriorate to the 'very poor' category from Thursday onwards, according to the Air Quality Early Warning System.

People woke up to a hazy morning on Thursday as a thin layer of smog blanketed the city, with the Air Quality Index (AQI) of 278, according to the morning air quality bulletin issued by the Central Pollution Control Board (CPCB).

After two days of slight improvement, Delhi's air quality has worsened again, plunging back into the 'very poor' category on Thursday, with stubble burning emerging as a major contributor and no respite expected anytime soon.

The 24-hour average Air Quality Index (AQI), reported at 4 pm every day, stood at 311, placing Delhi in the 'red zone', according to data from the Central Pollution Control Board (CPCB).

Delhi ranked fourth among the most polluted cities, with Rohtak topping the list in the ‘very poor’ category with an AQI of 348 out of 254 cities, according to the CPCB.

On Wednesday, Delhi's air quality had shown some improvement with an overall AQI of 202, as favourable wind conditions helped disperse pollutants.

The outlook for the subsequent six days also indicates that the city's air quality will continue to remain in the 'very poor' bracket.

Meanwhile, the daily mean of local and non-local fractional contribution to PM2.5 in Delhi by the DSS predicted that the contribution of stubble burning to Delhi's PM2.5 is estimated to be 21.5 per cent on Thursday, rising to 36.9 per cent on Friday, and 32.4 per cent on Saturday, up from just 1.2 per cent on Wednesday.

Satellite data showed that on Wednesday, 94 stubble-burning cases were detected in Punjab, 13 in Haryana, and 74 in Uttar Pradesh.

After stubble burning, transport is expected to be the second-highest contributor, accounting for 16.2 per cent on Thursday, 11.2 per cent on Friday, and 12.3 per cent on Saturday.

On the weather front, wind speed is expected to gradually increase, reaching up to 15 kmph from the northwest direction in the afternoon, before decreasing to below 10 kmph during the evening and Thursday night.

There will be a mainly clear sky with mist or haze.

Delhi has remained in the 'poor' category for the past two days — November 4 and 5 — with AQI below 300. Before that, the city had been in the 'very poor' category, with readings above 300.

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