Cleanest and Dirtiest Air in U.S. Revealed

Wildfires, intensified by climate change, played a major role in degrading global air quality in 2025. IQAir released its 8th annual World Air Quality Report, offering a comprehensive analysis of global air pollution data from 2025 and highlighting persistent health risks.

For this year’s report, IQAir analyzed data from monitoring stations across 9,446 cities in 143 countries, regions, and territories. Comparing this year’s report to the previous year, 54 countries experienced increases in annual average particulate matter 2.5 (PM2.5), 75 saw declines, two remained unchanged, and 12 were newly represented in this year’s dataset.

PM2.5 refers to fine inhalable particles, with diameters that are generally 2.5 micrometers and smaller, that can cause serious health problems when they are inhaled.

In 2025, 130 out of 143 countries/territories (91%) exceeded the World Health Organization’s (WHO) annual average PM2.5 guideline value. The world’s 25 most polluted cities were all located in India, Pakistan, and China, with India home to three of the four most polluted.

Only 14% of the world’s cities met the WHO standard in 2025, down from 17% a year earlier, with Canadian wildfires driving up PM2.5 across the United States and as far as Europe. Canada was the most polluted country in Northern America for just the second time in this report’s eight-year history, as its second-worst wildfire season on record affected air quality across Canada, the U.S., and parts of Europe.

In the United States, annual average PM2.5 levels increased to 7.3 micrograms per cubic meter (µg/m³). Smoke from wildfires in both Canada and the U.S. raised averages across parts of the Great Lakes states in the summer and in the Pacific Northwest in the fall.

The most polluted major U.S. city was El Paso, Texas. Historic dust storms triggered a 46% increase in PM2.5 levels to 11.4 µg/m³ as the city recorded the highest number of major pre-summer dust storms since the 1930s. 

The Southeast Los Angeles region (Cudahy, East Los Angeles, Huntington Park), heavily impacted by wildland-urban interface fires, ranked as the most polluted area in the country.

Seattle remained the cleanest major U.S. city for the second consecutive year, with an annual average of 4.5 µg/m³.

Only thirteen countries/territories met the WHO annual average PM2.5 guideline: French Polynesia, Puerto Rico, U.S. Virgin Islands, Barbados, New Caledonia, Iceland, Bermuda, Réunion, Andorra, Australia, Grenada, Panama, and Estonia.