Owing to unfavourable meteorological conditions for the dispersal of pollutants. Overall air quality in the national capital deteriorated to 'very poor' category on Sunday and is likely to go down further amid a dip in the mercury and wind speed. The city's 24-hour average air quality index (AQI) was 245 on Monday morning. It was 231 on Saturday, 137 on Friday, 302 on Thursday and 413 on Wednesday.
When it comes to assessing pollution in the air with AQI, 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".
According to the India Meteorological Department, the maximum wind speed was 15 KMPH on Saturday. It was 8 KMPH on Sunday and 11 KMPH on Monday and are predicted to slow down further. The winds were calm at night time. Over the next two days, therefore Delhi's air quality is likely to decline even more and remain in the 'poor' to 'very poor' category, it had said earlier.
The minimum temperature was 7 degrees Celsius on Sunday and the maximum is predicted to settle around 26 degrees Celsius, the weather department said. Calm winds and low temperatures trap pollutants close to the ground, while favourable wind speed helps in their dispersion. Mixing depth is the vertical height in 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 the average wind speed less than 10 KMPH, is unfavourable for dispersal of pollutants.
The share of stubble burning in Delhi's pollution has also reduced significantly as the harvesting season has ended. The impact of farm fire count in Punjab and Haryana is likely to be negligible on air quality of Delhi.
The contribution of stubble burning in neighbouring states to Delhi's PM2.5 levels was 6 per cent on Sunday, 4 per cent on Saturday, 2 per cent on Friday and just 1 per cent on Thursday, according to the Ministry of Earth Sciences' air quality monitor, SAFAR.