Morning after Dussehra, no sign of city's air improving

New Delhi: The national Capital's air quality was recorded in the 'very poor' category on Monday morning after Dussehra celebrations and the share of stubble burning in the city's PM2.5 pollution is likely to increase, according to a central government agency.

The Ministry of Earth Sciences' air quality monitor, SAFAR, said the wind direction and the wind speed is favourable for the transport of the pollutants from farm fires in Haryana, Punjab, and other neighbouring regions to Delhi.

The contribution of stubble burning in Delhi's PM2.5 concentration was 19 per cent on Sunday, it said. The city recorded an air quality index (AQI) of 343 at 10 am on Monday. The 24-hour average AQI was 349 on Sunday.

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'. Calm winds and low temperatures allow the accumulation of pollutants while favourable wind speeds help in their dispersion.

The central government's Air Quality Early Warning System For Delhi said the predominant surface wind direction is northwesterly with wind speed up to 12 kmph, which is favourable for the transport of pollutants from farm fires.

A large number of farm fires were observed over Punjab, Haryana and Uttar Pradesh, which is likely to impact Delhi-NCR's air quality, it said. The air quality warning system said the ventilation index - a product of mixing depth and average wind speed - is likely to be 15,000 metre square per second on Monday, which is also favourable for the dispersion of pollutants.

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 an average wind speed of less than 10 kmph, is unfavourable for the dispersal of pollutants.