According to the figures (till 9am Thursday) in the National Air Quality Index prepared by pollution-monitoring stations across Delhi, RK Puram had the highest level of PM 2.5 concentration at 405µg per cubic metre. This is nearly seven times the safe limit of 60µg per cubic metre.

According to the Central Pollution Control Board (CPCB), when air quality levels are “severe”, even healthy people are affected and those already suffering with diseases are seriously impacted.

RK Puram was followed by Anand Vihar with PM 2.5 concentration of 401 µg/m3, Punjabi Bagh (at 399 µg/m3) and Mandir Marg (at 372 µg/m3). The average level of PM 2.5 across seven pollution-monitoring stations of Delhi was 331, which is nearly five-and-a-half times the prescribed safe limit.

In the NCR region, levels of PM 2.5 in Faridabad, the city on the outskirts of Delhi, were recorded at 376 µg/m3.

The results are keeping in line with predictions of India’s meteorological department which had predicted that air pollution is likely to worsen after Diwali.

The air pollution forecast issued by the System of Air Quality and Weather Forecasting (SAFAR) of the ministry of earth sciences had issued a health warning on Monday, stating that there is serious risk of respiratory problems to people after prolonged exposure.

SAFAR had predicted that on Thursday, the day after Diwali, PM 2.5 level will increase from the average of the last 10 days by 148%. It had predicted that PM 2.5 will be near 430µg per cubic metre, which is more than seven times the safe limit of 60µg per cubic metre.

PM is found to be more harmful than other pollutants. They are of different sizes but among the most health-damaging ones are those that have a diameter of 10 microns or less (≤ PM10) as they penetrate and get lodged deep inside the lungs. Among PM, particles of size less than 2.5 micron are most deadly.

Once they enter the lungs, they restrict the availability of oxygen to lung muscles, affecting the cardiac rhythm and coul trigger heart attacks. They also cause inflammation of the lungs and increase the risk of blood clot formation and strokes. This could ultimately result in cardiovascular and respiratory diseases and lung cancers.

Like last year, authorities, including President Pranab Mukherjee, urged people to celebrate a pollution-free Diwali. Union environment minister Prakash Javadekar and Delhi chief minister Arvind Kejriwal made similar appeals.

Besides public appeals by leaders, students and schools across the city also urged people to stop using crackers on Diwali. For instance, some student groups distributed hand-written pamphlets requesting people to denounce crackers and celebrate Diwali with lights, and not crackers, for a safer future.

In the past few years, Delhi has earned the dubious tag of being the most polluted city in the world. In 2014, a World Health Organization study found the air in New Delhi to be the most polluted in the world. There were 12 other cities in the top 20 most polluted cities, among 1,600 cities studied.