Growing impacts of fire smoke on ozone pollution and associated mortality burden in the United States
2026-04-29
Fire smoke pollution is an emerging health risk factor, yet prior studies have focused mostly on fine particulate matter (PM 2.5 ) and neglected the health impacts from other pollutants, most notably ozone (O 3 ). Here, we quantify changes in ground-level O 3 concentrations during smoke episodes across the contiguous US using surface air quality measurements, satellite data, and machine learning models. After correcting for meteorological variability, smoke contribution to daily ground-level O 3 can reach up to 6.9 parts per billion (16% increase relative to nonsmoke days) at certain US monitoring locations, averaged over all smoke days from 2006 to 2023. Smoke O 3 patterns are poorly correlated with smoke PM 2.5 patterns, demonstrating that their health impacts do not necessarily coincide in space and time. We estimate that smoke O 3 can lead to 2045 annual excess deaths (95% confidence interval: 1325 to 2755) averaged across 2006 to 2023 using established exposure-response functions of all-source O 3 exposure. The increasing mortality due to smoke O 3 partially offset the observed declining trend in nonsmoke O 3 mortality. Over the study period, estimated deaths from smoke O 3 were equivalent to 15.8% of smoke PM 2.5 mortality, and this proportion reached 61.5% in 2023.