The IMD predicted low winds, poor ventilation coefficient and stable atmospheric conditions, likely to cause episodic severe air quality events. (Photo: File)

New Delhi: 'Severe' air pollution may return in the national capital in the run-up to New Year, the Met department has forecast, prompting the CPCB to direct agencies to step up action against polluting sources.

The concentration of pollutants will rise till at least December 29 due to low velocity wind and the coming down of the atmospheric layer where air and pollutants mix close to the surface.

Wind speed 900 metres above the ground may fall to 4 km/hr on December 29, the India Meteorological Department (IMD) said.

On December 27 and 28, it will be around 17 km/hr and 6 km/hr, respectively.

However, from December 30 wind speed may pick up a little and rise to 13 km/hr on the eve of New Year. 

Ground-level wind speed will be between 5 km/hr and 8 km/hr during this period, the IMD said.

The day's Air Quality Index (AQI) was 335, classified as 'very poor' by the CPCB, which may trigger respiratory illnesses on prolonged exposure.

"The IMD has predicted that low winds, poor ventilation coefficient and stable atmospheric conditions are likely to cause episodic severe air quality events particularly in the evening and night till December 29," CPCB's air lab chief Dipankar Saha said.

Poor ventilation coefficient essentially means that the ability of the atmosphere to dilute and disperse the pollutants over a region will reduce.

All these factors do not allow dispersion of pollutants leading to their accumulation in the air.

In view of the emerging situation, agencies concerned have been requested to remain alert and take all necessary measures for preventing emergency situation, Saha said.

In Delhi, agencies such as the Delhi Pollution Control Committee (DPCC) and the civic bodies are in charge of acting against open burning of waste, coal and firewood, visibly polluting vehicles, diesel generator sets, factors which spike pollution at the local level.