The national capital's air quality was recorded in the "poor" category on Monday morning, even as pollution levels dipped slightly due to favourable wind speed. However, the share of stubble burning in the city's pollution is likely to increase, according to the Ministry of Earth Sciences' Air Quality Early Warning System for Delhi.
On Sunday, a central government agency reported 1,230 farm fires in Delhi's neighbouring states -- the maximum in a day so far this season. The share of stubble burning in Delhi's PM2.5 pollution stood at 17 per cent on Sunday. It was 19 per cent on Saturday, 18 per cent on Friday, around one per cent on Wednesday and around 3 per cent on Tuesday, Monday and Sunday.
The city recorded an air quality index (AQI) of 232 at 8:45 am on Monday. The 24-hour average AQI was 254 on Sunday. It was 287 on Saturday, 239 on Friday and 315 on Thursday, the worst since February 12 (AQI 320). 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'.
During daytime, winds are blowing from the northwest, bringing pollutants from farm fires. At night, calm winds and low temperatures are allowing the accumulation of pollutants, according to an India Meteorological Department official.
The Ministry of Earth Sciences' Air Quality Early Warning System for Delhi said the ventilation index, a product of mixing depth and average wind speed, was 11,500 metre square per second on Sunday and is likely to be 10,000 metre square per second on Monday which is favourable for the dispersion of pollutants.
Mixing depth is the vertical height at which pollutants are suspended in the air. It reduces on cold days with calm wind speed. A ventilation index lower than 6,000 sqm/second, with an average wind speed of less than 10 kmph, is unfavourable for the dispersal of pollutants.
According to the Air Quality Early Warning System for Delhi, the impact of stubble burning is "restricted because of better mixing height and ventilation", but it is likely to rise on Monday. Union Environment Minister Prakash Javadekar had on Sunday said the pollution problem cannot be resolved in a day and continuous efforts are needed to tackle each of the contributing factors.
Interacting with people during a Facebook Live event, he said the major factors behind air pollution in the country are traffic, industries, waste, dust, stubble, geography and meteorology. The Central Pollution Control Board (CPCB) has said meteorological conditions in Delhi have been "extremely unfavourable" for the dispersion of pollutants since September as compared to last year.