"Air pollution threatens us all, but the poorest and most marginalized people bear the brunt of the burden", says Dr Tedros Adhanom Ghebreyesus, Director-General of WHO. About 3 billion people are breathing deadly fumes from domestic cooking stoves and fires, according to the Geneva-based agency.
While Delhi's air quality, according to the latest World Health Organization database for 2016, is at its worst, pollution bodies and the environment ministry say it's not a true reflection of the current reality because several measures and actions were taken in 2017, including implantation of the Graded Response Action Plan.
The World Health Organization says nine out of 10 people worldwide are breathing high levels of contaminants from both outdoor or ambient and household air pollution.
The organisation estimates that 4.2 million deaths in 2016 were caused by outdoor, or ambient, pollution and 3.8 million were caused by indoor pollution associated with the use of biomass fuel for heating and cooking.
It found more than 90 per cent of deaths occur in low- or middle-income countries, mainly in Asia and Africa.
Of the 2.2 million air pollution-related deaths in the region in 2016, 29 percent were due to heart disease, 27 percent stroke, 22 percent chronic obstructive pulmonary disease, 14 percent lung cancer, and 8 percent pneumonia.
Kanpur and Varanasi led the list of the world's most polluted cities, with Faridabad, Gaya, Patna, Lucknow, Agra, Muzaffarpur, Srinagar, Gurgaon, Jaipur, Patiala and Jodhpur also figuring in 20 most-polluted cities in the world.
It said the improvement in particulate matter concentration in Delhi has happened despite episodic events in two successive years in November 2016 and November 2017.
PM2.5 includes pollutants, such as sulfate, nitrates and black carbon, which pose the greatest risks to human health. "The cities which have invested in the capacity to regularly monitor and report the local air quality measurements have already demonstrated a commitment to starting to address air quality issues and public health", it said.
James Thornton, chief executive at environmental law charity ClientEarth, said: "These new statistics show a worrying level of this unsafe air pollution across the country".
Latest research by the World Health Organisation (WHO) shows that a total of 31 towns and cities of around 68 are either at or above the WHO's recommended limit value for the most unsafe toxic particles known as PM2.5.
The WHO has cited India's Pradhan Mantri Ujjwala Yojana that has provided an estimated 37 million women living below the poverty line free liquid petroleum gas connections, reducing their exposure to fuelwood emissions.
Air quality can also be influenced by natural elements, such as geographical, meteorological, and seasonal factors.
On Tuesday India's top court criticised authorities for failing to protect the Taj Mahal's pristine white marble from turning yellow because of air pollution.
"...[L] evels of contamination vary widely depending on government actions and financial resources". Countries need to work together on solutions for sustainable transport, more efficient and renewable energy production and use and waste management.