Automated screening method identifies recent probable wildland fire exceptional events for ozone and PM _2.5 across CONUS – Part 1

Wildfire events have driven a seasonal decline in air quality in recent years. The EPA's National Ambient Air Quality Standards are set to provide public health and welfare protection, but when a standard exceedance is outside the control of an air agency, such as in the case during many wildfires, an exceptional event demonstration can be developed to exclude data from attainment calculations. To evaluate and document probable exceptional events, we created a nationwide screening methodology to identify enhancements of PM_2.5 and ozone concentrations due to wildfire emissions. The screening methodology combines widely used wildfire data and tools, including NOAA's Hazard Mapping System data, PM_2.5 and ozone monitor data, modeled smoke PM_2.5 results, and Generalized Additive Modeling results. This screening identified regional wildfire trends in the data, including the year-round influence of smoke in the southeast U.S. due to agricultural burning and the significant impact of the 2021 and 2023 Canadian wildfire seasons on the northeastern U.S. Case studies on high- and low-frequency wildfire-impacted areas confirmed the efficacy of the screening method. Results suggest that roughly more than one third of the days from the 2020-2022 and 2021-2023 design value periods were characterized by an ozone or PM_2.5 smoke event somewhere in the country. Our results provide evidence of the scale to which wildfire smoke contributes to air pollution; this screening methodology can be used to identify probable wildfire exceptional smoke events.<i>Implications</i>: Wildfire events have driven a seasonal decline in air quality in recent years. The EPA's National Ambient Air Quality Standards are set to provide public health and welfare protection, but when a standard exceedance is outside the control of an air agency, such as in the case during many wildfires, an exceptional event demonstration can be developed to exclude data from attainment calculations. We created a nationwide screening methodology to identify enhancements of PM2.5 and ozone concentrations due to wildfire emissions. Our screening methodology can be used to identify probable wildfire exceptional smoke events.