Wildfire smoke has reversed years of progress toward meeting US ozone air quality standards, according to a new study published in Science. Researchers found that since 2015, ground-level ozone levels have stopped declining despite reductions in emissions from cars and industry, with wildfires now driving an increase in ozone pollution.
The study, led by Weizhi Deng, linked this reversal to emissions from wildfires, which release carbon monoxide and other gases that contribute to ozone formation. Smoke can travel hundreds of miles, causing elevated ozone levels far from the fire source. The researchers estimated that this rise in ozone has been associated with approximately 318 premature deaths per year since 2013.
Using a combination of satellite data, EPA monitoring station records, and meteorological data processed through deep learning models, the team found that ozone concentrations shifted from decreasing by 0.65 parts per billion (ppb) annually before 2015 to increasing by 0.13 ppb per year after that date. The EPA's monitoring network covers only 2% of the continental US land area, limiting direct ground measurements.
Wildfires have become more frequent and destructive due to climate change, with severe seasons in Canada and the western US. In California, the 2018 fire season killed 100 people, and 2020 burned 4.3 million acres. In January 2025, fires in Los Angeles killed 31 people and destroyed over 16,000 structures.
The study concludes that mitigating climate change and implementing fire prevention measures could improve air quality and benefit public health. Previous research has linked wildfire smoke to tens of thousands of premature deaths, with one 2024 study finding over 50,000 deaths in California over a decade from toxic particles in smoke.
