According to the World Health Organization (WHO), air pollution kills a staggering seven million people every year, while around 90 percent of the global population are breathing air containing high levels of pollutants.

Using data from the American Lung Association's 2024 State of the Air report, Visual Capitalist ranked the 21 most air-polluted cities in the US, based on their annual average PM2.5 concentrations.

PM2.5 refers to particulate matter that is 2.5 microns or less in diameter; tiny pollutants like these are particularly concerning because they can penetrate the bloodstream and cause a range of health issues. While the American Lung Association's annual average guideline for PM2.5 is 9 µg/m³, the WHO's limit is much lower, at 5 µg/m³.

America's most polluted city is Bakersfield, California, where the air has an average PM2.5 concentration of 18.8 µg/m³. In fact, of the ten most air-polluted US cities, six are in California — including Visalia (18.4 µg/m³), Fresno (17.5 µg/m³), the Bay Area (14.3 µg/m³), Los Angeles (14 µg/m³) and Sacramento (13.8 µg/m³).

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Via Visual Capitalist.