Marissa Childs, Mariana Martins, Andrew Wilson, Minghao Qiu, Sam Heft-Neal, Marshall Burke

Growing wildfire activity across North America produces significant smoke, undermining efforts to regulate surface air quality and protect public health. Using surface measurements, satellites, and machine learning, we provide granular, daily estimates of smoke PM2.5 concentrations in the contiguous U.S. from 2006 to 2023, and use them to assess the implications of smoke for surface air pollution and its regulation. From 2020 to 2023, population average smoke PM2.5 concentrations were 2.6–6.7 times higher than the 2006–2019 average, with exposure periods twice as long. The 5 worst exposure days in our sample period all occurred in 2023, a year with limited exposure in the western U.S. Wildfire smoke has recently driven 34% of monitoring stations above updated air quality standards, and is making the use of extreme event exemptions challenging. Without wildfire smoke, PM2.5 levels would have continued improving across the US.