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Exceptional Events

Exceptional Events

Exceptional events are unusual or naturally occurring events that can affect air quality but are not reasonably controllable using techniques that tribal, state or local air agencies may implement in order to attain and maintain the National Ambient Air Quality Standards (NAAQS). Exceptional events may include wildfires, high wind dust events, prescribed fires, stratospheric ozone intrusions, and volcanic and seismic activities.  For more information on exceptional events in general visit: US EPA's website for the Exceptional Event Rule.


Exceptional Event Demonstrations for 2020 and 2021 Wildfire Smoke

 Unusually high PM2.5 concentrations were recorded in the summers of 2020 and 2021 that exceeded the 2006 24-hour PM2.5 national ambient air quality standard of 35 ug/m3 in the Yuba City – Marysville area. The District prepared two Exceptional Event Demonstrations with the assistance of the California Air Resources Board (CARB), for submittal to the United States Environmental Protection Agency (USEPA). 

The analysis and data presented in the Demonstrations show that the unusually high concentrations were from wildfire smoke and that without the impacts, the 2020 and 2021 design value would have been below the standard.

2020 Exceptional Event Demonstration2021 Exceptional Event Demonstration

The 30-day public comment period required by 40 CFR 50.14(c)(3)(v) will begin on February 15, 2023, and will end on March 17, 2023. Comments on the Demonstrations can be submitted by mail to the District office addressed to: PM2.5 Maintenance Plan, FRAQMD, 541 Washington Avenue, Yuba City, CA 95991 or by email to After the comment period ends, the District will sumbit the Demonstrations and public comments received to CARB for submittal to the USEPA.  The District will request that the USEPA concur that the Demonstrations support the flagging of PM2.5 exceedances in this area as exceptional events due to wildfire smoke impacts from numerous fires in the State of California in accordance with 40 CFR 50.14.