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, fireworks, prescribed fires, stratospheric ozone intrusions, and volcanic and seismic activities.
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 2016 EPA Rule also included requirements for areas that commonly experience exceptional events to develop and submit to EPA mitigation plans that describe the steps agencies take to inform the public of when exceptional events occur, and how the public can mitigate their exposure to pollution from these types of events.
The District has developed a combined exceptional events mitigation plan that addresses all pollutants required to be addressed by EPA (PM10/PM2.5 wind-blown dust, PM10/PM2.5 wildfires, and PM2.5 fireworks). The plan has been submitted to the California Air Resources Board and EPA.