IOWA CITY — A NASA-funded study published in the journal Science on June 4 found that wildfire emissions have reversed a decade of U.S. ground-level ozone reduction. The research estimated that wildfire-driven ozone exposure resulted in an additional 318 premature deaths per year in the U.S. after 2013.
The study indicated that average national ground-level ozone concentrations increased by four percent beginning in 2015. Wildfire emissions have offset approximately four years of national ozone reduction progress since 2015, with regional deviations concentrated in the West and Midwest. From 2022 to 2024, wildfires exposed an additional 43 million people in the U.S. to ozone levels exceeding current federal air quality standards.
The analysis combined measurements from approximately 1,000 ground-based air quality stations with atmospheric model data, weather records, wildfire pollution data, and satellite imagery. Researchers used deep learning to construct a dataset estimating daily surface ozone concentrations from 2003 to 2024 on a one-kilometer grid across the contiguous U.S. Wildfires release carbon monoxide and other gases that react with sunlight and existing pollutants to form ground-level ozone.
Between 2003 and 2015, national ground-level ozone levels decreased by 11 percent following federal emissions regulations on power plants, vehicles, and diesel engines. The annual average of premature deaths linked to wildfire ozone after 2013 was 46 percent higher than in the previous decade. Smoke from the 2023 Canadian wildfires carried carbon monoxide downwind and produced elevated ozone levels across the U.S. Midwest, Northeast, and South. Jun Wang, an atmospheric scientist at the University of Iowa, said, "People in the Midwest may think fires burning far away will not affect them, but once wildfire pollution is in the air, it can move across regions. Pollution from one place can affect air quality in another."
The research received funding from a NASA health and air quality program and other agency grants. John Haynes, manager of NASA Earth Action's Health and Air Quality program, said, "NASA Earth observations, along with ground monitoring networks, help reveal air quality risks from wildfires that can cross state lines, giving air quality managers better decision-making information as wildfire smoke affects more communities."
NASA launched the TEMPO satellite in 2023 to provide hourly daytime air quality measurements over North America. The U.S. Environmental Protection Agency operates ground-level smog monitors in primarily urban locations, covering approximately two percent of the country.