Wildfire smoke has reversed US progress toward ozone air quality, study finds | US wildfires
The highly destructive wildfires that have hit the United States and North America in recent years have significantly increased emissions and been associated with tens of thousands of premature deaths; But according to new research, their impact on air quality is greater than previously known.
A published study Thursday in Science It found that wildfires since 2015 have reversed U.S. progress toward ozone air quality standards as worsening pollution caused by wildfire smoke has thwarted years of efforts to reduce emissions. According to the Environmental Protection Agency, ground-level ozone (O3) is formed when pollutants from cars, refineries, and industrial sources react with sunlight.
Wildfires also create their own major ozone problems because they emit carbon monoxide and other gases that can contribute to ozone formation, and smoke that can spread far beyond the fire source can cause increased ozone hundreds of miles away.
“Despite steady reductions in anthropogenic emissions of O3 precursors, observation stations indicate that policy-relevant surface O3 levels have stabilized,” Weizhi Deng and other authors wrote. In other words, although the emissions of chemicals that create ozone pollution have decreased, the decrease in the amount of ground level ozone has stopped.. The study links this plateau with wildfire emissions and finds that the increase in O3 emissions is associated with approximately 318 premature deaths each year since 2013.
The study noted that because the U.S. Environmental Protection Agency’s monitoring stations cover only 2% of the land in the continental United States, there are limited ground measurements available to researchers.
However, researchers developed a data set by evaluating meteorological data, as well as information from satellites and the EPA, with deep learning models. Ultimately, they found that O3 went from decreasing by 0.65 parts per billion (ppb) per year before 2015 to increasing by 0.13 ppb per year after that year.
Wildfires are getting worse around the world as global warming is causing extreme fires, causing billions of dollars in damage and catastrophic loss of life. Canada and the American West have seen particularly devastating fires in recent years.
In California, 2018 brought the state’s deadliest fire season, with 100 deaths, while 2020 was the most severe fire season in terms of land burned, with 4.3 million acres burned. In 2025, 31 people died and more than 16,000 structures were destroyed in fires in Los Angeles.
Tackling the climate crisis, which is creating conditions for more frequent and more destructive wildfires, is an important step in reducing pollution.
“Mitigation of climate change and implementation of fire prevention measures could lead to improved standards in air quality and potentially provide major benefits to public health,” the study states.
The findings add to a growing body of research that aims to shed light on the extent to which wildfires affect the environment and people. Wildfire smoke contains PM2.5, microscopic particles that can settle deep in the lungs and enter the bloodstream. The contaminant has been linked to numerous health conditions and premature deaths.
A 2024 study found that more than 50,000 people in California died prematurely over the decade due to exposure to toxic particles in wildfire smoke.
A study published last fall found that by the end of the century, smoke from wildfires is expected to kill as many as 1.4 million people a year worldwide unless emissions are stopped. Another study found that at the current rate of warming, wildfire smoke will kill more than 70,000 people each year in the United States by 2050.
