Exceptional Events

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Exceptional events are unusual or naturally occurring events that can affect air quality but are not reasonably controllable using techniques that the District may implement in order to attain and maintain the National Ambient Air Quality Standards. Exceptional events can include wildfires, high wind, stratospheric ozone intrusions and volcanic and seismic activities.

The Exceptional Events Rule

In September of 2016, the Environmental Protection Agency (EPA) finalized revisions to the Exceptional Events Rule to establish criteria and procedures for use in determining if air quality monitoring data has been influenced by exceptional events. The rule:

• applies to all exceptional event types and all national ambient air quality standards (NAAQS),
• ensures that air quality measurements are properly evaluated and characterized with regard to their causes,
• identifies reasonable actions that the District should take to address the air quality and public health impacts caused by these types of events,
• avoids imposing unreasonable planning requirements on air quality agencies related to violations of the NAAQS due to exceptional events, and
• ensures that the use of air quality data, whether afforded special treatment or not, is subject to full public disclosure and review.

Without the exceptional event determination, naturally occurring exceedances could negatively impact designation and attainment statuses.  Upon reviewing all the flagged data, the demonstration package justifying exclusion, and considering public comment - the EPA may concur that an event qualifies as exceptional.  If so, the associated data will be excluded from all regulatory determinations, helping our District to attain and maintain the National Ambient Air Quality Standards.