Report: Half of Americans breathing dangerous levels of air pollution

A new report shows that 46 percent of Americans — roughly 156 million people — are living in places that have received failing grades for air quality. The number of people breathing harmful air has increased by almost 25 million compared to last year, and is the highest in the past decade.

The American Lung Association’s “State of the Air” report is an annual publication, marking its 26th edition this year. It tracks levels of two of the most dangerous and widespread pollutants, ozone and particle pollution.

What is ozone pollution?

Ozone (O₃) is a gas with a molecular structure composed of three oxygen atoms. It forms in the lower atmosphere when pollutants from fossil fuel combustion form a chemical reaction in sunlight. Ozone levels tend to be highest in areas and on days with high emissions, warm temperatures and a lot of sunshine.

Ozone irritates the lungs when inhaled, causing inflammation and other damage. High ozone levels can cause chest tightness, coughing, and shortness of breath, and increases both the risk of developing and the severity of existing respiratory conditions like asthma and chronic obstructive pulmonary disease (COPD).

Ozone exposure has also been shown to increase the likelihood of metabolic disorders like diabetes, reproductive and developmental harm, and cardiovascular disease. Research shows that even short-term exposure to ozone levels below the current national ambient air quality standard (70 parts per billion (ppb) measured over eight hours) likely increases the risk of premature death.

What is particle pollution?

Particle pollution, aka particulate matter (PM), refers to small particles in the air we breathe.  Particle pollution is sometimes emitted directly from a source, such as construction sites, unpaved roads, or open fires, but most particles form in the atmosphere as a result of chemical reactions involving pollutants emitted from power plants, industrial processes and vehicles that burn fossil fuels.

There are two main categories of PM. Particles with diameters that are 10 micrometers and smaller are called PM10 and include dust, pollen and mold spores. Ultrafine particles with diameters that are 2.5 micrometers and smaller are called PM2.5 – these are at least 30 times smaller than the width of a human hair and are especially dangerous due to their ability to penetrate deep into human tissues.

PM2.5 pollution can be deadly even at low levels or during short-term exposure. In fact, the World Health Organization (WHO) sets the safe limit for average annual levels to just 5 micrograms per cubic meter (μg/m³), while the US national standard used in the report is 9 μg/m³.

The report states that researchers estimate PM2.5 is responsible for more than 50,000 yearly premature deaths in the United States alone. Most of these deaths are from respiratory and cardiovascular causes.

Particle pollution also has harmful effects that are not always lethal, including lung damage, heart attacks, strokes, COPD, asthma attacks, and lung cancer. PM exposure also increases the chance of developing diabetes and dementia in adults, increases the risk of preterm birth and infant mortality, and has been found to impair neurological development and cognition in children.

Climate change setbacks

While overall air quality has significantly improved since the passage of the emissions-regulating Clean Air Act in 1970 (a time when US cities were covered in dense smog blankets), progress is now stagnating.

The 2025 State of the Air report (which presents data from 2021-2023, the most recent three years of quality nationwide data that are publicly available) warns that the climate crisis is negatively impacting air quality due to more frequent and intense wildfires and heatwaves.

The authors also note that while poor air quality was mostly concentrated in western states in past years, its distribution is shifting eastward, with 2023 bringing unprecedented summer temperatures and wildfire smoke to Eastern states.

Population and air pollution

Another reason that further air improvements are difficult to achieve (not mentioned in the report) is continued US population growth, combined with the snail pace of transport electrification and Americans’ extreme car dependence. Vehicle traffic is a major source of air pollution, and more people still means more harmful emissions and a higher number of individuals exposed to pollution.

The cities with the worst air quality

The authors used three measures of pollutants to determine how different areas rank for air quality: ozone, short-term particle pollution (spikes in daily PM levels, which wildfires can cause), and long-term particle pollution (PM levels averaged over the year).

In the 2025 State of the Air report, the metropolitan areas that ranked worst for all three measures are unchanged from last year’s report.

Los Angeles has been the city with (by far) the worst ozone pollution for 25 of the 26 reporting years. Visalia (CA), Bakersfield (CA), Phoenix (AZ), Fresno (CA), Denver (CO), Houston (TX), San Diego (CA), Salt Lake City (UT), and (Dallas (TX) were also among the top 10 most polluted metropolitan areas for ozone.

Bakersfield (CA) also had the worst short-term particle pollution for the third straight year, as well as the worst level of year-round particle pollution for the 6th year in a row. Other top offenders for short-term PM levels were Fairbanks (AK), Eugene (OR), Visalia (CA), Fresno (CA), and Reno (NV).

For annual PM levels, Bakersfield (CA), Visalia (CA), Fresno (CA), Eugene (OR), Los Angeles (CA), and Detroit (MI) ranked the worst.

The cities with the best air quality

Not all US cities have terrible air, although the number of cities with low pollution levels is dwindling. According to the report, only 35 of the cities for which there is monitoring data had zero high ozone days and 22 cities had zero days with high levels of short-term particle pollution. The authors note that this represents a significant deterioration from last year’s report, when 55 cities had no days of high ozone and 75 had no spikes in particle pollution.

For year-round particle pollution, some of the cleanest cities included Casper (WY), Urban Honolulu (HI), Kahului (HI), Bozeman (MT), and Bangor (ME).

Bangor (ME) was one of two cities that rank on the cleanest cities lists for all three pollution measures. The other is San Juan, Puerto Rico. Both cities earned an A for ozone and short-term particle pollution and are among the 25 cities with the lowest year-round particle levels. Last year’s report included six cities (including these two) on the cleanest lists for all three pollution measures, but four of these had at least one bad particle pollution day this time around.

Persistent inequalities

The report notes that the burden of polluted air is not shared equally across the country, with people of color and low-income communities suffering the worst impacts (as with every other environmental crisis). While people of color make up around 41 percent of the national population, they make up half of the people living in a county with at least one failing air quality grade.

Trump actions endanger hard-won progress

This report comes as the Trump administration is attempting to roll back some vital air quality regulations, posing a real risk of more rapid deterioration.

The authors warn that sweeping Environmental Protection Agency (EPA) staff layoffs and federal funding cuts “are stymieing the agency’s ability to ensure that people have clean air to breathe.”

Trump is also pushing the EPA to reconsider existing emissions regulations, including limits on particle pollution, and has directed the EPA to exempt almost 70 coal-fired power plants (which produce some of the deadliest air pollution) from emission cuts requirements.