99% of the world breathes polluted air

The most damaging air pollutant for human health is PM2.5 — fine particles small enough to lodge deep in the lungs and enter the bloodstream. By WHO's assessment, about 99% of the global population lives in places where PM2.5 exceeds its air-quality guideline.

A leading environmental killer

Air pollution is linked to roughly 7 million premature deaths a year when both outdoor (ambient) and household sources are counted. PM2.5 specifically was associated with about 4.9 million deaths in 2023 (Health Effects Institute). It contributes to heart disease, stroke, lung cancer and respiratory illness, and is especially harmful to children and older adults.

Sources and hotspots

The main sources are fossil-fuel combustion in power, transport and industry, plus household cooking and heating with solid fuels, agricultural burning and wildfires. Exposure is highest across parts of South Asia, the Middle East and Africa, though no region meets the guideline everywhere.

The good news

Air quality is one of the most improvable indicators. Where governments have curbed coal burning, cleaned up vehicles and expanded clean cooking, PM2.5 has fallen quickly — and the same measures that cut particulates usually cut carbon emissions too. Monitoring networks and satellites now make it possible to track progress city by city, in near-real time.