Air pollution originates from numerous sources of emission, both natural and anthropogenic, with the latter becoming globally dominant since the beginning of industrialization. The process of combustion is the greatest contributor to air pollution, in particular, combustion of fossil fuels and biomass to generate energy. Outdoor combustion sources include ground, air, and water transport; industry and power generation; and biomass burning, which includes controlled and uncontrolled forest and savannah fires and agricultural waste burning as well as waste burning in urban areas. Other sources and processes contributing to outdoor pollution are re-suspension of surface dust and construction activities. Long-range atmospheric transport of pollutants from distant sources contributes to local pollution, particularly urban air pollution.

Over 90% of people live in places where the air is unhealthy to breathe, resulting in 4.2 million deaths globally each year (2016 data). Of all deaths from ambient air pollution, 38% were due to IHD, 20% were due to stroke and 43% were due to COPD.

Air pollution has an especially devastating impact on children’s health and has been linked to respiratory infections, adverse birth outcomes, adverse impacts on brain development and lung function, obesity, asthma, otitis media, cancers and increased mortality. Air pollution also disproportionally affects older people.