Delhi's air quality remains severe for second day: Authorities

Delhi's air quality remained in the "severe" category for the second consecutive day on Tuesday as high moisture and low wind speed prevented dispersion of pollutants.

Authorities said they were closely monitoring the situation.

Supreme Court-appointed Environment Pollution Control Authority (EPCA) Chairperson Bhure Lal said if "severe" conditions persisted for 48 hours, stringent action would be taken.

The stringent action includes emergency measures like car rationing and a ban on construction activities in the city.

Lal said if winds pick up speed, Delhi's air quality might improve, and hoped that rainfall predicted in the city will help bring down the pollution levels.

The Central Pollution Control Board (CPCB) recorded an overall air quality index (AQI) of 415.

An AQI between 201 and 300 is considered "poor", 301 and 400 "very poor" and 401 and 500 "severe".

The AQI on Monday was recorded at 412.

According to experts, even healthy people find it hard to breathe amid "severe" pollution levels and doctors advise physical activity to be kept at a minimum.

On Tuesday, neighbouring Ghaziabad, Noida and Faridabad also recorded "severe" air quality. Ghaziabad's air quality was the worst with an AQI of 429, the CPCB data showed.

Gurgaon recorded "very poor" air quality, it said.

Twenty-one areas in Delhi recorded "severe" air quality and ten areas recorded "very poor" air quality, the added.

Rohini, Sonia Vihar, Burari and Wazirpur edged towards "severe plus emergency" category, the CPCB said.

The overall PM2.5 level -- fine particulate matter in the air with a diameter of less than 2.5 micrometre -- was recorded at 261 and the PM10 level at 449, it said.

The Centre-run System of Air Quality and Weather Forecasting (SAFAR) said the air quality may recover slightly to "very poor" by Wednesday.

Meteorological conditions leading to insufficient rain often cause deterioration of the air quality. Delhi is currently witnessing the said phenomenon, it said.

"There is a fall in temperature and good amount of moisture is present in the air. Moist air is passing over Delhi's cool surface leading to fog formation and calm winds are not allowing pollutants to disperse," the SAFAR said.

"Levels of gaseous pollutants, NOx and CO, are forecast to be enhanced, up to moderate range, after a long time due to a fall in boundary layer height and reduced vertical mixing," it said.

According to the Indian Institute of Tropical Meteorology, the maximum ventilation index is likely to be 2,500 sqm/second from December 10-12.

The ventilation index lower than 6,000 sqm/second with average wind speed less than 10 kmph is unfavourable for dispersion of pollutants.

Air quality is likely to deteriorate marginally on Tuesday under the low wind and lower ventilation index, the IITM said.

The wind speed, ventilation index and higher moisture are highly unfavourable for dispersion of pollutants, it added.