Abstract
We examined PM(2.5) and Hazard Mapping System smoke plume satellite data at ∼600 United States (US) air monitoring stations to identify surface smoke on 14.0% of all May-September days for 2018-2023, with large influences in 2020 and 2021, due to California fires, and 2023, due to Canadian fires. Days with smoke have an average of 11 μg m(-3) more PM(2.5) and 8 ppb higher maximum daily 8 h average (MDA8) O(3) concentrations than nonsmoke days, and they also account for 94% of all days that exceed the daily PM(2.5) health standard (35 μg m(-3)) and 36% of all days that exceed the O(3) health standard (70 ppb). To estimate the smoke contributions to the O(3) MDA8, Generalized Additive Models (GAMs) were built for each site using the nonsmoke day data and up to 8 predictors. The mean and standard deviation of the residuals from the GAMs were 0 ± 6.1 ppb for the nonsmoke day data and 4.3 ± 7.9 ppb for the smoke day data, indicating a significant enhancement in the MDA8 O(3) on smoke days. We found positive residuals on 72% of the smoke days and for these days, we calculate an average smoke contribution to the O(3) MDA8 of 7.8 ± 6.0 ppb. Over the 6 year period, the percentage of exceedance days due to smoke in the continental US was 25% of all exceedance days, and the highest was in 2023 (38%). In 2023, the Central US experienced an unusually high number of exceedance days, 1522, with 52% of these impacted by smoke, while the Eastern US had fewer exceedance days, 288, with 78% of these impacted by smoke. Our results demonstrate the importance of wildland fires as contributors to exceedances of the health-based national air quality standards for PM(2.5) and O(3).