"Major sources of air pollution include inefficient modes of transport, household fuel and waste burning, coal-fired power plants, and industrial activities," Xinhua news agency quoted Farhan Haq, the Deputy UN spokesman, as saying at a daily news briefing here.

The world's population reached 7.35 billion in 2015, according to UN figures.

"However, not all air pollution originates from human activity, " he said. "For example, air quality can also be influenced by dust storms, particularly in regions close to deserts."

Some 6.5 million people are dying annually from air pollution, the UN agency said, adding that nearly 90 per cent of the deaths occur in low- and middle-income countries, with nearly two out of three occurring in the South-east Asia and Western Pacific regions.

"Fast action to tackle air pollution can't come soon enough," the top UN World Health Organisation (WHO) environmental official, Maria Neira, said of the new air quality model.

"Solutions exist with sustainable transport in cities, solid waste management, access to clean household fuels and cook-stoves, as well as renewable energies and industrial emissions reductions, "Neira added.

"Air pollution continues to take a toll on the health of the most vulnerable populations -- women, children and the older adults," WHO's Assistant Director General Flavia Bustreo said. "For people to be healthy, they must breathe clean air from their first breath to their last."