How many Americans are breathing unhealthy air?

Nearly half of Americans are breathing unhealthy air, which is considered unsafe due to high levels of ozone and particulate pollution, according to the American Lung Association's latest annual State of the Air report. 

At least 156 million Americans – approximately 46% of the population – live in areas with unsafe pollution levels. The report - which analyzed air quality data between 2021 and 2023 - found exposure to ozone and particulate pollution increased during this period. The analysis coincided with Canada's worst wildfire season on record, significantly impacting air quality across the U.S.

"The biggest thing that has saved patients' lives in regard to lung health and overall health is the Clean Air Act," Dr. Panagis Galiatsatos, a pulmonologist at the Johns Hopkins School of Medicine, said. "Clearly, legislation is needed because that's what dictates the air quality you breathe."

Of the 885 counties with air quality monitoring data, 480 failed at least one of the three pollution measures used in the report. The association ranked pollution levels in counties and cities from best to worst, using a scale from F to A.

The report revealed at least 42 million people live in counties that failed all three pollutant standards. These findings come when President Donald Trump's administration is working to loosen environmental regulations and cut funding for air quality research. He recently issued an executive order to increase coal mining and usage. 

"We're slashing unnecessary regulations that targeted the beautiful, clean coal," Trump said when signing the order. "I'm also directing Secretary Wright to use billions of dollars of federal funding to invest in the next generation of coal technology," he added, referring to Energy Secretary Chris Wright.

Environmental experts warn a resurgence in coal power plants would increase particulate pollution and carbon emissions, as well as toxic components such as mercury. This potential policy shift contrasts with the previous Biden administration's efforts to improve air quality through tighter rules for vehicle emissions and power plant regulations.

The number of Americans living in counties with unhealthy ozone levels increased by 24.6 million from the previous report, which covered 2020-2022. More than 125 million people now face unsafe ozone levels, with 93 additional counties failing the ozone measure compared to the last report.

Wildfire smoke from Canada drove much of this change as it traveled south and east, shifting the ozone burden to the Plains, Midwest, and Eastern U.S. While California retained its position as the state with the most metropolitan areas suffering high levels of ozone pollution, cities including Chicago, New York, and St. Louis joined the list of the most ozone-polluted urban centers.

For particulate pollution smaller than 2.5 microns across – known as PM2.5 – the report found daily exposure affects at least 77 million people, the largest population impacted in the last 16 years. About 85 million people live in counties that do not meet the Environmental Protection Agency's standards for annual exposure to PM2.5.

The report also highlighted significant disparities in pollution exposure among different demographic groups. People of color are more than twice as likely to live in communities with high ozone and particulate pollution compared with white people. Hispanic communities face even greater risks, being three times as likely to be exposed to air that had at least one poor air quality measurement.

"We have clean air policies, and they have led to improvements," Regan Patterson, an environmental justice researcher at the University of California, Los Angeles, said. "It's important to see if these have reduced, or even eliminated, air quality exposure disparities, and we are seeing that they have not."

Only two cities met the report's qualifications for clean air this year: Bangor, Maine, and San Juan, Puerto Rico. These cities had no days with extremely high ozone or PM2.5 pollution and ranked among the 25 cities with the lowest annual PM2.5 levels.

While air quality in the U.S. has generally improved since the Clean Air Act was enacted in 1970, with levels of key pollutants dropping by nearly 80%, millions of Americans still breathe polluted air daily. This exposure leads to both acute and chronic health conditions that, in some cases, increase the risk of early death.

Gaps in air quality monitoring limit the report's findings. Roughly two-thirds of counties in the U.S. lack air quality monitoring for ozone or particulate pollution. A study published in Proceedings of the National Academy of Sciences estimates 50 million people – more than 15% of the U.S. population – live in places without reliable air quality monitoring.

"Any estimate we have about health and its relationship with pollution is an underestimate," Nelson Roque, who studies environmental health at Pennsylvania State University and was lead author of the study, said.

While extraordinary by historical standards, the climate conditions that fueled the destructive Canadian wildfires may become more common. Climate projections suggest such hot and dry weather could be typical by the 2050s if the world continues on its current trajectory of global warming, potentially worsening air quality issues in the future.