Two days before Diwali, the national capital's air quality dropped to season's worst on Friday. with the decreased wind speed leading accumulation of pollutants and affecting dispersion.The Supreme Court-mandated Environment Pollution (Prevention and Control) Authority is expected to take a call on Friday on several recommendations made by a 10-member anti-pollution task force.The recommendations include banning construction work at night in Delhi-NCR from October 26 to 30 and closure of industries that have not switched to piped natural gas.The city's overall air quality index (AQI) stood at 315 at 8:30 am on Friday, while it was 311 on Thursday evening.Most of the places in the national capital recorded the AQI in the "very poor" category, while the situation inched towards "severe" in some areas.The Ministry of Earth Sciences' air quality forecast and research service, SAFAR, said, "The decrease in wind speed has started to negatively influence Delhi's air quality by drastically decreasing ventilation coefficients and thereby affecting dispersion."Calm surface winds will continue for the next two days. Consequently, the AQI is predicted to oscillate between high and middle range of the "very poor" category, it said.The System of Air Quality and Weather Forecasting and Research (SAFAR) said another western disturbance is likely to affect the western Himalayan region by October 28. In view of this, the situation on Diwali may not be as bad as last year.“While harsher winter conditions are yet to set in and the weather during the period of analysis has remained relatively favourable (including a delayed monsoon), several ongoing systemic actions and preventive emergency measures had also contributed to prevent an early onset of very poor and severe pollution in Delhi-NCR. The scenario has changed on Diwali night,” said Anumita Roychowdhury, executive director, research and advocacy, CSE.