More than 95 percent of the world’s population is breathing polluted, unsafe air and the hardest hit areas are in Africa and Asia, a major study of global air pollution has found.

Urban areas, which are home to a greater percentage of the world’s population than ever before, are exposing hundreds of millions to air that is filled with pollution from automobiles and factories. In many rural areas, the burning of solid fuels like wood, charcoal and coal, is also a threat.

The report, known as the State of Global Air and produced by the Health Effects Institute, analyzed satellite data and other air-quality monitors to figure out what percentage of the world is exposed to air polluted above levels that the World Health Organization deems as safe.


dirty air map

Global map comparing 2016 fine particulate matter concentrations to World Health Organization air quality guidelines and interim target (IT) levels (Health Effects Institute)

According to the report, indoor and outdoor forms of air pollution contributed to an estimated 6 million deaths worldwide in 2016—accounting for an increased risk of stroke, heart attack and lung cancer. Regions with the highest concentration of pollution include countries in North and West Africa, as well as South Asia.

The report found that China, which has instituted some measures to improve its notoriously foul air after widespread protests, has seen its air pollution exposures stabilize and even begin to slightly decline.

“There are reasons for optimism, though there is a long way to go,” Bob O’Keefe, vice-president of the institute, told The Guardian. “China seems to be now moving pretty aggressively, for instance, in cutting coal and on stronger controls. India has really begun to step up on indoor air pollution through the provision of LPG [liquefied petroleum gas] as a cooking fuel, and through electrification.”

The report joins a growing list of studies that have detailed the negative effects of air pollution on overall health and well-being.

A recent study found that contaminated air, water and land led to 6 million premature deaths worldwide in 2015, while a separate report found that many Americans are breathing contaminated air despite existing limits on air particle pollution.