Public Notice: Exceptional Event Demonstration for Omak Air Monitoring Site in Washington
Summary
"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. Exceptional events may include wildfires, high wind dust events, prescribed fires, stratospheric ozone intrusions, and volcanic and seismic activities.
The Confederated Tribes of the Colville Reservation (CCT) is requesting that EPA concur on its request to exclude certain data from the Air Quality System database as being impacted by exceptional events.
EPA and the CCT have developed a draft demonstration (see "Event Details" below) explaining how certain Omak monitoring site data from 2022 and 2023 meet the criteria for exclusion under the Exceptional Events Rule.
EPA is providing the public with an opportunity to review and comment on the draft demonstration.
Event Details
The Confederated Tribes of the Colville Reservation (CCT) operate an air quality monitoring site in Omak, Washington (Air Quality System ID 530470013). In summer of 2022 and 2023, the monitoring site recorded exceedances of the annual fine particulate matter national ambient air quality standard (2024 annual PM2.5 NAAQS).
The CCT and EPA Region 10 worked collaboratively to prepare a weight-of-evidence analysis showing that smoke from wildfires was transported to the Omak monitoring site and caused exceedances on 26 days in 2022, between August and October, and on 26 days in 2023, between July and September.
A copy of the draft demonstration is available for review:
About the Exceptional Events Rule
To address high monitor values resulting from exceptional events not reasonably controllable or preventable, EPA promulgated the Exceptional Events Rule (EER), pursuant to Section 319 of the Clean Air Act. The EER allows air agencies to flag air quality data as exceptional and request that EPA exclude those data from use in regulatory determinations if EPA concurs that the air agency’s demonstration satisfies EER requirements.
As set forth in 40 CFR 50.14, the EER applies to the treatment of data showing exceedances or violations of any NAAQS for purposes of, among other things, an action by the Administrator to designate an area, pursuant to Clean Air Act Section 107(d)(1), or redesignate an area, pursuant to Clean Air Act Section 107(d)(3), for a particular national ambient air quality standard.
The data requested for exclusion in this demonstration have regulatory significance because they will be used by EPA to designate areas for the 2024 annual PM2.5 NAAQS.
Under 40 CFR §50.14(c)(3)(iv), demonstrations justifying data exclusion as exceptional must include the following:
- A narrative conceptual model that describes the event(s) causing the exceedance of violation and a discussion of how emissions from the event(s) led to the exceedance or violation at the affected monitor(s).
- A demonstration that the event affected air quality in such a way that there exists a clear causal relationship between the specific event and the monitored exceedance or violation.
- Analyses comparing the claimed event-influenced concentration(s) to concentrations at the same monitoring site at other times to support the clear causal relationship requirement.
- A demonstration that the event was both not reasonably controllable and not reasonably preventable.
- A demonstration that the event was a human activity that is unlikely to recur at a particular location or was a natural event.
- Documentation that the State followed the public comment process and conducted at least a 30-day comment period.
Learn more: Treatment of Air Quality Monitoring Data Influenced by Exceptional Events