Exceptional Events

Exceptional events are unusual or naturally occurring events that can affect air quality but are not reasonably controllable using techniques that agencies implement in order to attain and maintain the National Ambient Air Quality Standards (NAAQS). Exceptional events are events for which the normal planning and regulatory process established by the Clean Air Act (CAA) is not appropriate. The Exceptional Events Rule (EER), codified at 40 Code of Federal Regulations (CFR) Parts 50.1, 50.14, and 51.930, allows states to petition EPA to exclude air quality monitoring data influenced by exceptional events from applicable regulatory determinations.

DAQ submits Exceptional Event Demonstrations to EPA when ambient air monitoring data is affected by an exceptional event, in accordance with the EER. These events can include natural events such as high-winds, wildfires, stratospheric ozone intrusions, and volcanic and seismic activities. Federal regulations also allow states to petition to exclude data when exceedances or violations are caused by emissions from fireworks displays on a case-by-case basis.

Mitigation of Exceptional Events

40 CFR 51.930(a) requires that states requesting to exclude air quality data due to exceptional events must take appropriate and reasonable actions to protect public health from exceedances or violations of the NAAQS. In its 2016 EER revision, EPA implemented a requirement for the development of mitigation plans for areas with historically documented or known seasonal events. Clark County was identified as an area subject to the new mitigation plan requirements for wildfire (ozone) and high wind (PM₁₀) events.

In October 2018, DAQ adopted the Clark County Mitigation Plan for Exceptional Events, which addresses the EPA-required plan components and encompasses wildfire (ozone and PM_2.5), high wind (PM₁₀), and fireworks (PM_2.5) events. The plan outlines the programs, systems, and control measures in place to protect the public and mitigate the impact of these types of events in Clark County. EPA Region 9 determined that the plan was complete for PM₁₀ due to high wind dust and ozone due to wildfires in a letter dated December 17, 2018. The mitigation plan was approved by the Clark County Board of County Commissioners (BCC) on January 21, 2020, and supersedes the Natural Events Action Plan approved by the BCC on March 15, 2005.

Exceptional Event Demonstrations
Demonstrations Available for Public Comment
Please visit our Public Notices page to view demonstrations currently out for public comment.

Demonstrations Submitted to EPA for Action

Date	Pollutant	Monitor	Type	Status
July 31, 2023 Demonstration Appendix	PM₁₀	Multiple	High Winds	Deferred Review
February 21, 2023 Demonstration Appendix	PM₁₀	Multiple	High Winds	Deferred Review
October 22, 2022 Demonstration Appendix	PM₁₀	Multiple	High Winds	Deferred Review
September 8-9, 2022 Demonstration Appendix	PM₁₀	Multiple	High Winds	Deferred Review
May 28-29, 2022 Demonstration Appendix	PM₁₀	Multiple	High Winds	Deferred Review
May 8, 2022 Demonstration Appendix	PM₁₀	Multiple	High Winds	Deferred Review
April 11, 2022 Demonstration Appendix	PM₁₀	Multiple	High Winds	Deferred Review
February 21, 2022 Demonstration Appendix	PM₁₀	Multiple	High Winds	Deferred Review
October 25, 2020 Demonstration Appendix	PM₁₀	Multiple	High Winds	Deferred Review
September 8, 2020 Demonstration Appendix	PM₁₀	Multiple	High Winds	Deferred Review
September 26, 2020 Demonstration Appendices	Ozone	Multiple	Wildfire	Deferred Review
September 2, 2020 Demonstration Appendices Addendum	Ozone	Multiple	Wildfire	Deferred Review
August 18-21, 2020 Demonstration Appendices	Ozone	Multiple	Wildfire	Deferred Review
August 7, 2020 Demonstration Appendices	Ozone	Multiple	Wildfire	Deferred Review
August 3, 2020 Demonstration Appendices	Ozone	Multiple	Wildfire	Deferred Review
June 26, 2020 Demonstration Appendices Addendum	Ozone	Paul Meyer	Wildfire	EPA Nonconcurrence 4/11/2022
June 22, 2020 Demonstration Appendices Addendum	Ozone	Multiple	Wildfire	EPA Nonconcurrence 4/11/2022
May 28, 2020 Demonstration Appendices Addendum	Ozone	Multiple	Stratospheric Intrusion	Deferred Review
May 9, 2020 Demonstration Appendices Addendum	Ozone	Multiple	Stratospheric Intrusion	EPA Nonconcurrence 4/11/2022
May 6, 2020 Demonstration Appendices Addendum	Ozone	Multiple	Stratospheric Intrusion	EPA Nonconcurrence 4/11/2022
August 6–7, 2018 Demonstration Appendices	Ozone	Multiple	Wildfire	Deferred Review
July 30-31, 2018 Demonstration Appendices	Ozone	Multiple	Wildfire	Deferred Review
July 25-27, 2018 Demonstration Appendices	Ozone	Multiple	Wildfire	Deferred Review
July 14-17, 2018 Demonstration Appendices	Ozone	Multiple	Wildfire	Deferred Review
June 27, 2018 Demonstration Appendices	Ozone	Multiple	Wildfire	Deferred Review
June 23, 2018 Demonstration Appendices	Ozone	Multiple	Wildfire	Deferred Review
June 19–20, 2018 Demonstration Appendices	Ozone	Multiple	Wildfire	EPA Nonconcurrence 4/11/2022
July 3, 2013 Demonstration	Ozone	Multiple	Wildfire	Deferred Review
May 4, 2013 Demonstration	Ozone	Multiple	Wildfire	Deferred Review
April 15, 2013 Demonstration	PM₁₀	Multiple	High Winds	Deferred Review
May 23, 2012 Demonstration	Ozone	Multiple	Wildfire	Deferred Review
May 10, 2012 Demonstration	PM₁₀	Multiple	High Winds	Under EPA Review
July 3, 2011 Demonstration	PM₁₀	Multiple	High Winds	EPA Concurrence 6/25/14
May 21, 2008 Demonstration	PM₁₀	Craig Road	High Winds	Under EPA Review
Feb 13, 2008 Demonstration	PM₁₀	Craig Road	High Winds	Under EPA Review
June 29-30, 2005 Demonstration	Ozone	Multiple	Wildfire	Under EPA Review

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