The WHO linked about 4.3 million of those deaths to indoor air pollution and about 3.7 million deaths to outdoor air pollution. (There was likely overlap between people exposed to indoor and outdoor air pollution, which explains the total estimate of about 7 million deaths.) Most of the indoor air pollution resulted from the use of coal, wood, or biomass stoves, and overall, low- and middle-income countries in Southeast Asia and the Western Pacific bore the brunt of 2012’s air-pollution death toll—3.3 million deaths in those regions resulted from indoor air pollution and 2.6 million to outdoor air pollution, according to the WHO’s estimates.
“Cleaning up the air we breathe prevents non-communicable diseases as well as reduces disease risks among women and vulnerable groups, including children and the elderly,” Flavia Bustreo, the WHO’s assistant director-general for family, women and children’s health, told Nature.
Last year, the WHO’s cancer arm, International Agency for Research on Cancer (IARC), officially classified air pollution as a carcinogen.