1. Only 17% of global cities meet WHO air pollution guideline.

2. Seven countries met the WHO annual average PM2.5 guideline of 5 µg/m3: Australia, Bahamas, Barbados, Estonia, Grenada, Iceland, and New Zealand.

3. The five most polluted countries in 2024 were:
• Chad (91.8 µg/m3) more than 18 times higher than the WHO PM2.5 annual guideline
• Bangladesh (78.0 µg/m3) more than 15 times higher than the WHO PM2.5 annual guideline
• Pakistan (73.7 µg/m3) more than 14 times higher than the WHO PM2.5 annual guideline
• Democratic Republic of the Congo (58.2 µg/m3) more than 11 times higher than the WHO PM2.5 annual guideline
• India (50.6 µg/m3) more than 10 times higher than the WHO PM2.5 annual guideline

4. A total of 126 (91.3%) out of 138 countries and regions exceeded the WHO annual PM2.5 guideline value of 5 µg/m3.

5. Byrnihat, India was the most polluted metropolitan area of 2024, with an annual average PM2.5 concentration of 128.2 µg/m3. The region of Central & South Asia was home to the top nine most polluted cities in the world. India was home to six of the nine most polluted global cities.

6. The most polluted major U.S. city was Los Angeles, California. Ontario, California was the most polluted city in the United States. Seattle, Washington was the cleanest major city in the U.S.

7. Mayaguez, Puerto Rico was the cleanest metropolitan area of 2024, with an annual average PM2.5 concentration of 1.1 µg/m3.

8. PM2.5 concentrations decreased in every country in Southeast Asia, though transboundary haze and lingering El Niño conditions remain major factors.

9. In Africa, the scarcity of real-time, publicly accessible air quality monitoring data is so severe that there is only one monitoring station for every 3.7 million people.

10. Wildfires in the Amazon rainforest impacted vast areas of Latin America in 2024, with PM2.5 levels in some cities across Brazil’s Rondônia and Acre states quadrupling in September.

11. Oceania is the world’s cleanest region, with 57% of regional cities meeting the WHO PM2.5 annual guideline value of 5 µg/m3.