National Capital Delhi and Prime Minister Narendra ModiÂs Parliamentary constituency Varanasi are among the most polluted cities that figure in the list of 20 most polluted cities in the world.

The listing has been done in terms of PM2.5 levels in 2016, data released by the World Health Organisation (WHO) has shown. The WHO data also said that nine out of 10 people in the world breathe air containing high levels of pollutants. Other Indian cities that registered very high levels of PM2.5 pollutants were Kanpur, Faridabad, Gaya, Patna, Agra, Muzaffarpur, Srinagar, Gurgaon, Jaipur, Patiala and Jodhpur.

Other highly polluted cities include Ali Subah Al-Salem in Kuwait and some cities in China and Mongolia.

In terms of PM10 levels, 13 cities in India figured among the 20 most-polluted cities of the world in 2016. WHO has called upon member-countries in its Southeast Asia Region to aggressively address the double burden of household and ambient (outdoor) air pollution, saying the region, which comprises India, accounts for 34 pc or 2.4 million of the seven million premature deaths caused by household and ambient air pollution together globally every year.

Of the 3.8 million deaths caused by household air pollution globally, the region accounts for 1.5 million or 40% deaths, and of the 4.2 million global deaths due to ambient air pollution, 1.3 million or 30% are reported from the region, it said. The PM2.5 includes pollutants like sulfate, nitrate and black carbon, which pose the greatest risk to human health.

WHOÂs global urban air pollution database measured the levels of fine particulate matter (PM10 and PM2.5) from more than 4,300 cities in 108 countries, according to which ambient air pollution alone caused some 4.2 million deaths in 2016, while household air pollution from cooking with polluting fuels and technologies caused an estimated 3.8 million deaths in the same period.

Since 2016, over 1,000 additional cities have been added to WHOÂs database, which shows more countries are measuring and taking action to reduce air pollution than ever before. ÂWHO estimates that around 7 million people die every year from exposure to fine particles in polluted air that penetrate deep into the lungs and cardiovascular system, causing diseases including stroke, heart disease, lung cancer, chronic obstructive pulmonary diseases and respiratory infections, including pneumonia, the report said.

More than 90% of air pollution-related deaths occur in low- and middle-income countries (including India), mainly in Asia and Africa, followed by low- and middle-income countries of the Eastern Mediterranean region, Europe and the Americas, the report said.

ÂAround 3 billion peopleÂmore than 40% of the worldÂs populationÂstill do not have access to clean cooking fuels and technologies in their homes, the main source of household air pollution, it said.

It said the WHO recognises air pollution is a critical risk factor for noncommunicable diseases (NCDs), causing an estimated 24% of all adult deaths from heart disease, 25% from stroke, 43% from chronic obstructive pulmonary disease and 29% from lung cancer.

ÂAir pollution threatens us all, but the poorest and most marginalised people bear the brunt of the burden. It is unacceptable that over 3 billion peopleÂmost of them women and childrenÂare still breathing deadly smoke every day from using polluting stoves and fuels in their homes, said Tedros Adhanom Ghebreyesus, director-general of WHO.

Major sources of air pollution from particulate matter include inefficient use of energy by households, industry, agriculture and transport sectors, and coal-fired power plants. In some regions, sand and desert dust, waste burning and deforestation are additional sources of air pollution.