Co-occurrence of boreal smoke plumes and enhanced surface ozone across the central USA during summer 2023

From May 20 through July 25, 2023, large boreal forest fire plumes were transported across the central and eastern United States of America. On many days the U.S. Environmental Protection Agency (EPA) air quality monitoring network detected co-located ozone and PM2.5 anomalies, which indicate a contribution from the smoke to surface ozone production. We apply a general additive mixed model (GAMM) to interpolate the observed ozone and PM2.5 observations onto daily maps of the continental United States.  Comparison to a recent baseline period with below-average wildfire activity (2014, 2016, 2019) allows for the identification of smoke events that contributed to enhanced surface ozone levels.