Water, Waste & Pollution
Air pollution
The contamination of indoor or outdoor air by chemical, physical or biological agents, responsible for millions of premature deaths each year and the largest environmental threat to human health.
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The presence of harmful substances in the air — including fine particulate matter (PM2.5 and PM10), ozone, nitrogen dioxide, sulphur dioxide and carbon monoxide — from sources such as fossil fuel combustion, industry, transport, agriculture and household burning of solid fuels. WHO attributes about 6.7 million premature deaths annually to the combined effects of ambient and household air pollution.
References
4.2 million ambient deaths (2019); 6.7 million combined ambient + household; 99% of population above guideline levels; disease breakdown; policy levers.
State of Global Air figure of 7.9 million premature deaths (broader methodology); second-leading cause of death in young children; life-expectancy impact.
Overview
What it means
Ambient (outdoor) air pollution caused an estimated 4. 2 million premature deaths in 2019, mainly via cardiovascular and respiratory disease and cancers; 89% of these deaths occur in low- and middle-income countries. In that year, 99% of the world's population lived in places not meeting WHO air quality guideline levels.
Household air pollution — largely from cooking with solid fuels — disproportionately affects women and children.
How it is used
Air pollution is monitored through ground stations, satellites and health-burden assessments such as the State of Global Air. Policies target key sources: cleaner transport, efficient homes, cleaner power and industry, and better waste management. It features in the Sustainable Development Goals (targets 3. 9 and 11. 6) and drives national air quality standards.
Why it matters
Air pollution is widely described as the largest environmental threat to human health, killing more people annually than tobacco. Because its main sources overlap with fossil fuel use, air quality policy and climate policy are deeply linked — cleaner air measures often deliver health benefits within weeks or months.
Definitions and controversy
Mortality totals vary by study and methodology (WHO combined estimate ~6. 7 million; State of Global Air ~7. 9 million) — figures should be quoted with their source and year.
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