New Delhi is blanketed in acrid smog each year, primarily blamed on stubble burning by farmers in neighbouring regions to clear their fields for ploughing. Air pollution is expected to worsen during the Hindu festival of lights, Diwali, which falls on November 1 this year when smoky fireworks spewing hazardous toxins are part of celebrations.

Levels of fine particulate matter – cancer-causing microparticles known as PM2.5 pollutants that enter the bloodstream through the lungs – surged to nearly 23 times the World Health Organization recommended daily maximum.

The pollutants topped 344 micrograms per cubic metre, according to monitoring firm IQAir on Wednesday, which listed air in the sprawling megacity of some 30 million people as “hazardous”, ranking it as the world’s worst.

Government efforts have so far failed to solve the country’s air quality problem, and a study in the Lancet medical journal attributed 1.67 million premature deaths in 2019 to air pollution in the world’s most populous country.