The overall air quality of the Capital was in the higher end of the moderate category on Sunday and is expected to remain at the edge of the category for the next three days, according to government-run monitoring agency SAFAR (System of Air Quality and Weather Forecasting and Research).
“AQI [Air Quality Index] is forecast to stay at the edge of moderate category for the next three days as ventilation coefficient is still moderately high due to not so calm prevailing surface winds,” SAFAR said in a statement.
Though stubble burning fires were observed on Saturday around Punjab, Haryana, and border regions and boundary layer wind direction is favourable for transport of its effect towards Delhi, higher local wind speed is preventing accumulation of pollutants in the city.
Also, only a marginal stubble impact on AQI is expected for the next two days, according to SAFAR.
The AQI on Sunday was 184, which is “moderate” and slightly less than 189 on Saturday, according to CPCB.
“Currently, about half the stations in Delhi are in the poor category and the rest in moderate. So, the overall AQI is moderate. Local wind speed is above 4 km/hr and the ventilation coefficient (VC) is about 4,000. But later this week, the probability of the air quality turning poor is very high,” a SAFAR official told The Hindu.
VC is the product of mixing height (the height of the atmosphere up to which pollutants can be dispersed) and average wind speed. So, a higher VC means that mixing height and wind speed at high and this aids in better dispersion of pollutants and hence reduce pollution.