A study led by Minghao Qiu of Stony Brook University, published on May 8 in Science Advances, finds that wildfire smoke has significantly increased ground-level ozone and contributed to excess deaths from wildfire smoke in the United States each year. The research covers nearly two decades of data and was conducted with collaborators at Stony Brook University.
The findings are important because previous studies have focused mainly on dangerous particulates from wildfires while largely overlooking ozone. Ozone is an invisible but strong oxidant linked to respiratory and cardiovascular problems, reduced cognitive performance, and increased mortality.
“As we move further into spring and then summer, wildfires will most likely increase in the United States and all of North America, and scientists should be thinking about the effects of increased ozone from fires in addition particulates emitted into the air,” said Qiu, corresponding author, assistant professor in the School of Marine and Atmospheric Sciences (SoMAS)Â and core faculty in the Program in Public Health at Stony Brook University. The study was led by Yangmingkai Li, a visiting undergraduate researcher at SoMAS.
Qiu said that scientists have primarily focused on wildfire impacts on particulate matter pollution but have not had a systematic understanding of wildfire effects on ozone over the U.S. This study combined surface ozone measurements from 2006 to 2023 with meteorological data and satellite information using machine learning models to quantify changes during fire episodes across the continental U.S. Researchers used National Oceanic and Atmospheric Administration (NOAA) satellite data to identify smoke days for comparison with non-smoke days while controlling for temperature and ultraviolet radiation.
The results show that wildfire smoke can boost daily ground-level ozone by as much as 16 percent in some regions such as the eastern U.S. and Midwest—enough to increase illnesses or deaths related to fire smoke exposure. The team estimates more than 2,000 excess deaths per year among Americans are linked specifically to this rise in ozone caused by wildfires.
Qiu emphasized two key points: “The true health effects and death toll from wildfire smoke are likely higher than previously thought, given that prior research has not factored in ozone exposure,” he said; “Even days with relatively good visibility post wildfires may still contain unseen ozone from fires that harm health because particulate matter pollution and ozone pollution do not often overlap.” In this study mortality estimates were reported only for people ages 65 or older due to how exposure-response functions were derived.
Researchers note their findings suggest increases in wildfire-driven ozone threaten progress made toward cleaner air nationwide by partially offsetting long-term declines both in overall levels of ground-level ozone as well as related mortality rates.
