Wildfire smoke offsets decades of progress in reducing ozone exposure across the United States

Minghao Qiu , Yangmingkai Li, Marissa Childs, Makoto Kelp, Xiaomeng Jin, Guanyu Huang, Mahdieh Danesh Yazdi, Yaguang Wei, Yuan Wang, Kai Chen

Ground-level ozone (O3) pollution has declined in the U.S., yet the progress has stalled in recent years, coinciding with increasing wildfire smoke. Using ensemble machine learning models trained on surface observations, we develop a gridded daily smoke O3 dataset across the contiguous U.S. from 2006-2023. We estimate that wildfire smoke placed an additional 29 million people each year in areas exceeding the federal O3 standard, a 74% increase over a no-smoke baseline. Smoke has offset 36% of the reduction in the O3 nonattainment population and 62% of the improvement in population-weighted O3 concentrations over 2006-2023. Smoke ozone follows spatial-temporal patterns distinct from smoke PM2.5. Wildfire smoke is increasingly eroding the O3 health benefits achieved through decades of emission controls, posing a growing challenge for air quality management in a changing climate.