Congress in 2005 identified a need to account for events that result in exceedances of the National Ambient Air Quality Standards (NAAQS) that are exceptional in nature (e.g., not expected to reoccur or caused by acts of nature beyond man-made controls). In response, the U.S. Environmental Protection Agency (EPA) promulgated the Exceptional Events Rule (EER) to address exceptional events under 40 CFR Parts 50 & 511 and 72 FR 13560 2 | Learn More > 

Due to the arid nature of the state, Arizona is susceptible to both windblown dust events and smoke events from forest fire, both of which may qualify as exceptional events. These events may be captured by various air quality monitoring equipment throughout the state, sometimes resulting in exceedances or violations of the NAAQS. The EER allows for states and tribes to "flag" air quality monitoring data as an exceptional event and exclude that data from use in determinations with respect to exceedances or violations of the NAAQS, if the EPA concurs with the demonstration submitted by the flagging agency.

See Arizona’s Natural and Exceptional Events Demonstration Documentation | View Documents >