Delhi has been blanketed in a toxic fog the morning after the Hindu festival of Diwali, when people in the capital celebrate by setting off crackers and fireworks.
Air quality in the Indian capital, one of the world’s most polluted cities, is usually very poor – but the density of some harmful particles and droplets in the air spikes for days after Diwali and can reach up to 42 times the safe limit.
An air quality station in Chanakyapuri recorded a PM2.5 level of 999 on Monday morning. India’s pollution control board sets the safe limit for PM2.5 – which measures particulate matter smaller than 2.5 micrometres – at 60.
The highest PM2.5 level recorded in London on Monday morning was 139.
PM2.5 particles and droplets are considered to be the most harmful kind of air pollution because they are fine enough to evade the body’s natural filters, penetrate the lungs and enter the bloodstream.
Short-term exposure can trigger coughing and eye and throat irritation, while longer term exposure is strongly associated with reduced lung function, heart disease and lung cancer.
A 2015 study found about half of Delhi’s 4.4 million schoolchildren had compromised lung capacity and would never completely recover. India also has the world’s highest rate of death from respiratory disease, according to the World Health Organisation (WHO), with 159 deaths per 100,000 people in 2012, about five times that of the UK and twice that of China.
“The levels we’re seeing are really alarming. They are clearly in the severe category,” said Anumita Roychowdhury, the executive director of the Centre for Science and Environment, a Delhi-based think-tank.
“Delhi’s air remains so polluted throughout the year that it doesn’t really have room for additional pollution during Diwali.”
She said the smog released by the fireworks was worsened by the cooler temperature and slowing winds, which meant “the air doesn’t blow away, and all the pollution that happens inside the city gets trapped at the ground level, very close to our noses”.
The city authorities have piloted a scheme allowing vehicles to only drive on alternate days, depending on whether their last registration number was odd or even.
Unlike in China, where a PM2.5 reading greater than 300 for more than three days triggers a “red alert” that closes schools, there are no official government warnings over high levels of air pollution.
The capital region’s high court last year criticised the inaction of Delhi and national governments in dealing with the problem and compared the city to “a gas chamber”.
Roychowdhury said awareness of the problem was slowly growing among Delhi’s residents. “Newspapers are writing about it every day, it’s part of the dinner table conversation,” she said.
“Where we still have a lot more to do is to sensitise people about the solutions to the problem. We need to understand that controlling it needs hard decisions, and to build public support for these hard decisions.”