The deterioration in air quality was largely due to the cold wave and associated meteorological conditions that have made dispersal of pollutants hard.
Based on CPCB task force recommendations, the Supreme Court-appointed Environment Pollution Control Authority (EPCA) shut down industries located in hotspot industrial areas of Wazirpur, Mundka, Narela, Bawana, Sahibabad and Faridabad and halted construction activities across Delhi-NCR till December 26. "At AIIMS, we have observed that there is about 15 to 20 per cent rise in such cases", Dr Randeep Guleria, Director, AIIMS, said. We sanctioned one of largest metro phases yesterday.
"The wind speed and ventilation index are highly unfavourable for dispersion of pollutants", it had said. At 409 on Tuesday, the air quality index (AQI) relented from the 448 on Monday when officials announced curbs on construction activity for two days as an emergency measure. In RK Puram, the concentration of PM 2.5 was recorded at 288 on Tuesday, significantly down from Monday's level of 698.
Surface wind speeds have come down and the mixing height or room available for vertical dispersion has come down as well. Experts say that the "severe" air quality level makes breathing hard even for healthy people.
AQI at Punjabi Bagh Delhi was recorded poor, PM 2.5 was at 349 while the PM 10 was at 222.
The task force also urged people to avoid using private vehicles, particularly those using diesel as fuel, and minimise outdoor exposure for the next three to five days, especially those with respiratory illness, the CPCB said.
The air quality in the national capital improved and settled at "very poor" category on Wednesday, even as Delhi continued its battle with pollution.
An AQI above 400 falls in the "severe" category.
Officials said they are closely monitoring the situation and if these conditions persist for 48 hours, then stringent action would be taken.
The index was 5500 sqm/second on Wednesday, the IITM said.
The advisory also recommended frequent wet mopping and using masks known as N-95 or P-100 respirators only for outdoor activities.