The vast majority of the most polluted cities in the world are in India according to a new study from IQ AirVisual and Greenpeace.

Gurugram, a northern Indian city in the state of Haryana, is the world's most polluted city, while New Delhi, the country's capital, is ranked 11th worst globally.

Researchers studied the amount of fine particulate matter known as PM2.5 to gauge the extent of air pollution.

PM2.5, or particles of 2.5 micrometers or less in diameter, are dangerous because it lodges deep in the lungs.

The World Health Organisation (WHO) sets a daily mean air quality guideline of just 25 micrograms of PM2.5 per cubic meter of air.

According to the report, Gurugram's annual average concentration is 135.8 micrograms per cubic metre, which AirVisual classifies as "very unhealthy".

New Delhi toxic smog pushes air pollution to peak levels Show all 14 1 /14 New Delhi toxic smog pushes air pollution to peak levels New Delhi toxic smog pushes air pollution to peak levels India's Rashtrapati Bhawan is partly visible due to smog as traffic plies on Rajapth. Smog levels spike during winter in Delhi, when air quality often eclipses the World Health Organization's safe levels AP New Delhi toxic smog pushes air pollution to peak levels Cooler air traps pollutants -- such as from vehicles, building sites and farmers burning crops in regions outside the Indian capital -- close to the ground AP New Delhi toxic smog pushes air pollution to peak levels A man wearing a protective mask walks amidst smog in the early morning in New Delhi Reuters New Delhi toxic smog pushes air pollution to peak levels Indian people receive treatment for respiratory problems at a hospital in New Delhi AFP/Getty New Delhi toxic smog pushes air pollution to peak levels Buildings shrouded in smog Reuters New Delhi toxic smog pushes air pollution to peak levels A combination of pictures showing people wearing face masks to protect themselves against air pollution AFP/Getty New Delhi toxic smog pushes air pollution to peak levels Indian workers are seen in the morning smog as they clean a lane littered with remains of firecrackers AP New Delhi toxic smog pushes air pollution to peak levels Smog envelopes the horizon in New Delhi AP New Delhi toxic smog pushes air pollution to peak levels Motorists on a busy road amid heavy smog AFP/Getty New Delhi toxic smog pushes air pollution to peak levels A man cycles past a government building amid heavy smog AFP/Getty New Delhi toxic smog pushes air pollution to peak levels Commuters are seen amid heavy smog in New Delhi AFP/Getty New Delhi toxic smog pushes air pollution to peak levels An Indian shepherd walks along his herd of sheep amidst heavy smog AFP/Getty New Delhi toxic smog pushes air pollution to peak levels A train moves through heavy smog EPA New Delhi toxic smog pushes air pollution to peak levels A pedestrian crosses a road near the Indian President's house AFP/Getty

According to the WHO, seven million people die from air pollution each year, with nine out of 10 people globally breathing in polluted air.

In New Delhi the average annual concentration is 113.5 micrograms per cubic metre.

The city – found to be the world's most polluted capital – is notorious for its toxic air, which is caused by vehicle and industrial emissions, dust from building sites, smoke from burning rubbish and crop residue in nearby fields.

"Air pollution steals our livelihoods and our futures, but we can change that. In addition to human lives lost, there’s an estimated global cost of 225 billion dollars in lost labour, and trillions in medical costs," said Yeb Sano, executive director of Greenpeace Southeast Asia.

"This has enormous impacts, on our health and on our wallets."

Although Indian cities fare poorly in the new study, Greenpeace and AirVisual said conditions had improved drastically in China.

Average PM2.5 concentrations in cities in China fell by 12% from 2017 to 2018, according to Greenpeace.

China struggled for years to enforce environment rules and crack down on polluting industries, but it has benefited recently from vastly improved legislation and greater political will to combat poor air quality.

Dehli smog during morning commute

"In mainland China, in particular, this has led to significant improvements in year-on-year reductions in PM2.5 levels," the groups said in the study.

"The question which remains to be answered is whether there is enough political will to aggressively fight the health emergency India faces today and move away from polluting fuels and practices," said Pujarini Sen, spokeswoman for Greenpeace India.