The Exceptional Event Rule (EER) governs the review and handling of air quality monitoring data influenced by exceptional events. If a State adequately demonstrates that an exceptional event has caused an exceedance or violation of National Ambient Air Quality Standards (NAAQS), then that data can be excluded from regulatory determinations such as nonattainment designations. Examples of exceptional events are: chemical spills, structural fires, exceedances due to transported pollution, exceedances due to a terrorist attack, natural events (natural disasters, volcanic and seismic activities, high wind events, wildfires and wildland fire use fires, stratospheric ozone intrusions) and prescribed fire.
States, Tribes, or local air quality agencies must collect monitoring data, and may flag events they believe to fall under this rule, and submit demonstration information to the EPA. For an event to qualify under the EER, it must meet the four criteria below.
Currently, wildfires can frequently contribute to NAAQS exceedances for ozone and PM2.5 while prescribed fire infrequently contribute to exceedances. The 2007 EER considered wildfires as natural events and prescribed fire as an exceptional event on a case by case basis.
Important: In Fall 2016 the EER was revised by EPA. Changes include a description of fires using only the terms 'wildfire' and 'prescribed fire' and several fire-related definitions. More language was included recognizing both the ecological role of fire, and prescribed fire as an anthropogenic event, but one that could also be a viable exceptional event.
The revised rule also contains conditions under which prescribed fires could qualify as exceptional events, which include the use of smoke management programs (SMP) and the application of basic smoke management practices (BSMP). The full text of the rule, and information such as fact sheets and guidance on implementation are available at the EPA’s Exceptional Events Rule Guidance page.
About the Exceptional Events Rule
US EPA. 2016. Exceptional Events Rule and Guidance. Accessed 3 January 2017. Available at: https://www.epa.gov/air-quality-analysis/exceptional-events-rule-and-guidance
US EPA. 2007. Treatment of Data Influenced by Exceptional Events: Final Rule. Accessed 3 January 2017. Available at: https://www.federalregister.gov/documents/2015/11/20/2015-29350/treatment-of-data-influenced-by-exceptional-events#h-21