El Paso and Los Angeles were among the most polluted areas in the United States last year, according to a new air quality report that evaluated pollution levels around the world in 2025.
The report is the latest iteration of a global analysis that the Swiss technology company IQAir publishes annually. This one centered on some of the causes of declining air quality worldwide, including wildfires, which the report’s authors cited as a leading driver of the downward trend.
Fires played a sizable role in U.S. pollution levels, according to the report. It found that air quality worsened overall for the country, with average pollutant levels increasing by 3% between 2024 and 2025. Air pollution in a particular location was measured as the concentration of pollutant per cubic meter of air in that location, where the pollutant is calculated in micrograms, on average for the year.
That’s based on an air quality standard set by the World Health Organization that recommends limiting exposure to air that exceeds 5 micrograms of pollutant per cubic meter. By the end of 2025, the average concentration of U.S. air pollutants had reached 7.3 on that scale.
Most-polluted U.S. cities
Air pollution levels varied by region and even by state, sometimes significantly, the report showed. In Texas, concentrations of pollutants dropped by 9% on average in some major cities, like Austin, Fort Worth and Houston, while skyrocketing in others, like El Paso. Historic dust storms that blanketed the area last spring sent pollution levels soaring, according to the report, which said those storms triggered a 46% increase.
East Los Angeles experienced one of the most severe air quality situations in 2025, which the report largely attributed to massive wildfires that devastated the city and the surrounding region. The collective pollution seen in East L.A. and nearby Huntington Park, Cudahy and Florence-Graham as a result of the fires made that part of Southern California the most polluted area in the country last year.
A number of other major U.S. cities ended 2025 with worse air quality than they had when it started, including Chicago, Los Angeles, New York City and Washington, D.C., according to the report. Denver’s average pollution level decreased slightly in that time, while some West Coast cities, like San Francisco and Seattle, consistently met the annual guidelines established by WHO.
Still, the report showed that western locations dominated the rankings for most polluted North American cities in 2025, with a majority in California.
Wildfires, industrial emissions
The report’s authors cited wildfires, including those that broke out in Canada last year during what became that country’s second-worst fire season on record, as one of the main causes of air pollution in North America last year.
Wildfire smoke can be a formidable source of pollution that is capable of seriously impacting human health through atmospheric emissions. The consequences of last year’s blazes on air quality were also exacerbated by dust storms, like the ones that struck El Paso, as well as transportation emissions, power generation and other industrial sources, the report said.
It specifically called out artificial intelligence data centers as “an emergent source” of air pollution. In 2025, the centers contributed “indirectly through the increased power plant emissions required to meet their massive energy demands, and directly through their reliance on diesel generators for backup power,” the report said.