Treatment of Data Influenced by Exceptional Events

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.

Contact:      Mark Evangelista
                    (919) 541-2803


In March of 2007, the Environmental Protection Agency (EPA) finalized 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:

  • ensures that air quality measurements are properly evaluated and characterized with regard to their causes,
  • identifies reasonable actions that should be taken to address the air quality and public health impacts caused by these types of events,
  • avoids imposing unreasonable planning requirements on state, local, and tribal 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.

Interpreting and implementing the 2007 Exceptional Events Rule has been challenging both for the air agencies developing exceptional events demonstrations and for the EPA regional offices reviewing and acting on these demonstrations. As a result of our experiences and stakeholder requests related to implementing the 2007 rule, the EPA developed and released Interim Exceptional Events Implementation Guidance documents in May of 2013, and acknowledged the need to consider additional changes that could only be accomplished through a notice-and-comment rulemaking.

Proposed Exceptional Events Rule Revisions and Draft Guidance (Posted: 11/10/15)

  • Federal Register Notice - Proposed revisions to the Exceptional Events Rule
  • Federal Register Notice - Extension of public comment period to February 3, 2016
  • Draft Guidance on the Preparation of Exceptional Events Demonstrations for Wildfire Events that May Influence Ozone Concentrations
  • Fact Sheet

Notice of Public Hearing on Proposed Exceptional Events Rule Revisions

  • Date:       Tuesday, December 8, 2015
  • Location:  Arizona Department of Environmental Quality
                   Room 3175
                   1110 W. Washington Street
                   Phoenix, Arizona 85007
                   10:00 am to 6:00 pm
  • For More Information and to Register: Contact Ms. Pamela Long, U.S. Environmental Protection Agency, telephone (919) 541-0641, email address See additional information in the SUPPLEMENTARY INFORMATION section of the proposed rule revisions. 

Notice of Informational Public Webinar to Discuss Proposed Rule Revisions and Draft Guidance

EPA hosted an informational public webinar on November 17, 2015 from noon -1:30 pm EST to provide an overview of the proposed Exceptional Events Rule revisions and the draft wildfire/ozone implementation guidance and to respond to clarifying questions regarding this action.

Quick-Reference Guide for Exceptional Events Demonstrations

This user-friendly quick-reference guide for exceptional events demonstrations is intended to direct air agency staff and other interested persons to specific information and guidance related to exceptional events demonstrations. The matrix pairs event and pollutant combinations (x-axis) with current Exceptional Events Rule criteria (y-axis). Each cell contains links that direct the user to specific example analyses or language that may be used in Exceptional Events Demonstrations. EPA expects to update this matrix as additional information (rule revisions, guidance, demonstrations) become available.

Examples of Reviewed Exceptional Event Submissions

This exceptional events submissions table provides examples of air agency-submitted and EPA concurred exceptional events demonstration packages along with the accompanying EPA concurrence letters and supporting analyses. EPA expects to update this table as additional demonstrations become available.

Best Communication Practices for Preparation of Exceptional Events Demonstrations

Because of the passage of time between issuing the 2013 Interim Exceptional Events Implementation Guidance and the EPA’s anticipated 2015 proposed revisions to the Exceptional Events Rule, the EPA hosted conference calls with some air agencies between September 2014 and March 2015 to ask whether any new exceptional events implementation concerns had arisen and to better understand currently employed exceptional events implementation processes and practices. As a result of these discussions, the EPA developed a list of best practices for communication and collaboration between the EPA and air agencies. The EPA will update this document, if needed, to reflect promulgated changes to the Exceptional Events Rule (if needed, revisions anticipated summer 2016).

Publicly Available Support Information and Tools

EPA provides no endorsement of specific publicly available tools, nor does EPA mandate their use. EPA believes that publicly available tools can provide supporting documentation for one or several of the exceptional event criteria within an air agency exceptional event demonstration, but EPA generally does not believe that links and/or references to these tools constitute a complete demonstration submittal.