A major new study has found that wildfires have completely reversed America's progress in fighting ground-level ozone pollution since 2015, undoing years of regulatory work and posing a mounting public health threat.
Researchers analyzing satellite data, EPA monitoring stations, and meteorological information discovered that ozone levels stopped declining and began rising after 2015, directly correlating with increased wildfire activity. The shift marks a dramatic reversal: before 2015, ground-level ozone was decreasing by 0.65 parts per billion annually. Since then, it has been rising by 0.13 parts per billion each year.
The findings, published Thursday in Science, quantify a problem that has largely escaped public attention even as wildfire smoke has choked communities across North America. Wildfires emit carbon monoxide and other gases that, when exposed to sunlight, form ground-level ozone. Unlike the ozone high in the atmosphere that protects Earth from UV radiation, ground-level ozone is a harmful air pollutant created primarily by reactions between emissions from cars, refineries, and industrial sources with solar radiation.
The smoke itself can drift hundreds of miles from where fires burn, spreading ozone-forming chemicals far beyond the fire's origin point. The study links the plateau in ozone reduction and subsequent rise to roughly 318 premature deaths annually since 2013.
Researchers faced a significant challenge in measuring the problem. EPA monitoring stations cover only 2 percent of land in the continental United States, leaving vast gaps in ground-level data. To overcome this limitation, scientists developed datasets using deep learning models that combined satellite information, EPA measurements, and meteorological data into a comprehensive picture of ozone trends across the country.
The scale of recent fire seasons underscores the urgency. California's 2018 fire season killed 100 people and was the deadliest on record. Two years later, the state experienced its most destructive fire season by acreage, with 4.3 million acres burned. Los Angeles fires in 2025 killed 31 people and destroyed more than 16,000 structures.
The health toll extends beyond immediate fire damage. Wildfire smoke contains PM2.5, microscopic particles that embed themselves deep in lungs and enter the bloodstream. A 2024 study found that more than 50,000 people in California died prematurely over a decade from exposure to these toxic particles in wildfire smoke alone. Research published last year projected that by 2050, wildfire smoke could cause more than 70,000 deaths annually in the United States at current warming rates, and as many as 1.4 million deaths globally by century's end unless emissions are curbed.
The researchers emphasized that addressing the underlying cause is essential. Mitigating climate change and implementing fire prevention measures represent the most direct paths to reversing the trend and improving air quality while reducing premature deaths tied to pollution exposure.
Author James Rodriguez: "Wildfires have become the enforcement officer reversing decades of clean air rules, and federal regulators seem caught flat-footed by the scale of the problem."
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