The gap in air quality between rich and poorer countries is increasing steadily, a new report by the World Health Organisation (WHO) has found
Air quality in more affluent states is slowly getting better, while the air in poorer countries is still getting worse, the study, which was released on Wednesday, said.
"Air pollution threatens us all, but the poorest and most marginalised people bear the brunt of the burden," WHO Director-General Tedros Adhanom Ghebreyesus said in a statement.
"It is unacceptable that over three billion people - most of them women and children - are still breathing deadly smoke every day from using polluting stoves and fuels in their homes," he added.
In total, 90 percent of people around the world are breathing polluted air, which kills about seven million annually, the WHO estimated.
The health agency conducted its research by comparing the number of small particles in the air.
These particles enter the lungs and cardiovascular system and can cause cancer, respiratory problems and chronic obstructive pulmonary diseases.
The vast majority of the deaths each year - more than 90 percent - occurred in low-income countries in Asia and Africa.
According to the data, air quality is the worst in the Middle East, Asia and Africa.
A big issue in these regions is the lack of access to clean cooking fuels and technologies in their homes, which leads to air pollution inside of homes.
Other things affecting air quality globally are polluting industries like transportation and intensive agriculture.
But the WHO also noted some positive trends.
It said air quality in richer countries had gradually improved in the past few years, while governments were taking air pollution more seriously, implementing rules and laws increasing the awareness about the issue.
"The good news is that we are seeing more and more governments increasing commitments to monitor and reduce air pollution, as well as more global action from the health sector and other sectors like transport, housing and energy," Tedros said.