A thick quilt of smog eclipsed Delhi skies on Wednesday morning as the city’s air quality level remained “severe” for the seventh consecutive day, data from the Central Pollution Control Board showed. The levels of toxic pollutants were alarmingly high even in Noida, Greater Noida, Ghaziabad, Faridabad and Gurgaon of the National Capital Region.

According to the agency’s air quality index or AQI, any reading above 100 on a scale of 500 is progressively unsafe for health. At 8 am, the AQI in Delhi was 476, indicating “severe” conditions that pose a risk of respiratory problems. On Tuesday, it was 476, and on Monday, the AQI of the city was 477.

The air quality, which includes the concentration of PM2.5 particles as well as bigger pollutants, in the neighbouring cities of Faridabad, Ghaziabad, Noida, Greater Noida and Gurugram also rose past 460.

While the pollution control board uses 24-hour average data, the Ministry of Earth Sciences’ SAFAR, or System of Air Quality and Weather Forecasting And Research, reports real-time figures. The government-run monitoring agency said the overall AQI was an unprecedented 724 in Delhi at 10 am.

On Tuesday, AQI in the city was in the “higher end of the severe category which is an unusual condition”, the agency said.

The Central Pollution Control Board index is typically lower than that of SAFAR in cases of extreme pollution because it averages values for 24 hours, and caps hourly indices at 500 even if they are of a higher value.

Levels of the most dangerous particles, called PM2.5, climbed to around 527 micrograms per cubic meter, which is considered hazardous to breathe. Particulate matter smaller than 2.5 microns (or about a ten-thousandth of an inch) is particularly dangerous to human health. Such particles are small enough to travel deep into the respiratory system, potentially impairing lung function. To be considered safe, the National Ambient Air Quality Standards require PM2.5 concentration to be less than 60 micrograms per cubic metre of air in any given 24-hour period.

The PM10 index, which measures the concentration of particulate matter of 10 microns diameter or less in the air, hit 819, SAFAR said. This is coarse particulate matter and mostly dust, which attaches to toxic material from other emissions. A level of 500 is considered “hazardous” and people are strictly advised to remain indoors.

SAFAR on Tuesday said a significant improvement in air quality is not likely in the coming two days because of slow wind speed, particularly during night time, entry of high moisture content, and agricultural fires in neighbouring states. As of Wednesday, stubble fires contributed 22% of the PM2.5 particles in Delhi’s air.

An office-goer walks past a traffic signal near Central Delhi on a smoggy morning on November 10. (Credit: Danish Siddiqui/ Reuters)

Delhi’s air pollution typically worsens in October and November due to farmers burning off stubble in neighbouring states, unfavourable wind speed and local emission of traffic fumes in the city. Firecrackers ignited for Diwali add to the problem.

Pollution in the city had almost disappeared earlier this year, when the Centre imposed a countrywide lockdown to contain the coronavirus but has returned since the government began lifting restrictions at the end of August.

Authorities have banned the sale and use of firecrackers ahead of the Diwali festival in a bid to control the situation, as the city faces one of the worst spells of pollution in years

The emergency situation this year also comes as Delhi is possibly suffering a “third wave” of coronavirus infections. Health experts worry that high air pollution levels over a prolonged period have compromised the disease resistance of people living in Delhi, making them more susceptible to the coronavirus.

On Saturday, the Indian Medical Association said the rise in new cases may be linked to air pollution. A day earlier, the health ministry had informed a parliamentary committee that air pollution may lead to faster spread of the coronavirus, as it causes coughing and sneezing.

Last month, the Indian Council of Medical Research had also said, citing international studies, that air pollution levels can lead to rise in coronavirus mortality.

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